| Message ID | 1481870510-44290-1-git-send-email-takafumi.kubota1012@sslab.ics.keio.ac.jp (mailing list archive) |
|---|---|
| State | Superseded |
| Headers | show |
On Fri, Dec 16, 2016 at 03:41:50PM +0900, Takafumi Kubota wrote: > This is actually inspired by Filipe's patch(55e3bd2e0c2e1). > > When submit_extent_page() in __extent_writepage_io() fails, > Btrfs misses clearing a writeback bit of the failed page. > This causes the false under-writeback page. > Then, another sync task hangs in filemap_fdatawait_range(), > because it waits the false under-writeback page. > > CPU0 CPU1 > > __extent_writepage_io() > ret = submit_extent_page() // fail > > if (ret) > SetPageError(page) > // miss clearing the writeback bit > > sync() > ... > filemap_fdatawait_range() > wait_on_page_writeback(page); > // wait the false under-writeback page > > Signed-off-by: Takafumi Kubota <takafumi.kubota1012@sslab.ics.keio.ac.jp> > --- > fs/btrfs/extent_io.c | 4 +++- > 1 file changed, 3 insertions(+), 1 deletion(-) > > diff --git a/fs/btrfs/extent_io.c b/fs/btrfs/extent_io.c > index 1e67723..ef9793b 100644 > --- a/fs/btrfs/extent_io.c > +++ b/fs/btrfs/extent_io.c > @@ -3443,8 +3443,10 @@ static noinline_for_stack int __extent_writepage_io(struct inode *inode, > bdev, &epd->bio, max_nr, > end_bio_extent_writepage, > 0, 0, 0, false); > - if (ret) > + if (ret) { > SetPageError(page); > + end_page_writeback(page); > + } OK...this could be complex as we don't know which part in submit_extent_page gets the error, if the page has been added into bio and bio_end would call end_page_writepage(page) as well, so whichever comes later, the BUG() in end_page_writeback() would complain. Looks like commit 55e3bd2e0c2e1 also has the same problem although I gave it my reviewed-by. Thanks, -liubo > > cur = cur + iosize; > pg_offset += iosize; > -- > 1.9.3 > > -- > To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in > the body of a message to majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html -- To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Thanks for your replying. I understand this bug is more complicated than I expected. I classify error cases under submit_extent_page() below A: ENOMEM error at btrfs_bio_alloc() in submit_extent_page() I first assumed this case and sent the mail. When bio_ret is NULL, submit_extent_page() calls btrfs_bio_alloc(). Then, btrfs_bio_alloc() may fail and submit_extent_page() returns -ENOMEM. In this case, bio_endio() is not called and the page's writeback bit remains. So, there is a need to call end_page_writeback() in the error handling. B: errors under submit_one_bio() of submit_extent_page() Errors that occur under submit_one_bio() handles at bio_endio(), and bio_endio() would call end_page_writeback(). Therefore, as you mentioned in the last mail, simply adding end_page_writeback() like my last email and commit 55e3bd2e0c2e1 can conflict in the case of B. To avoid such conflict, one easy solution is adding PageWriteback() check too. How do you think of this solution? Sincerely, On 2016/12/22 15:20, Liu Bo wrote: > On Fri, Dec 16, 2016 at 03:41:50PM +0900, Takafumi Kubota wrote: >> This is actually inspired by Filipe's patch(55e3bd2e0c2e1). >> >> When submit_extent_page() in __extent_writepage_io() fails, >> Btrfs misses clearing a writeback bit of the failed page. >> This causes the false under-writeback page. >> Then, another sync task hangs in filemap_fdatawait_range(), >> because it waits the false under-writeback page. >> >> CPU0 CPU1 >> >> __extent_writepage_io() >> ret = submit_extent_page() // fail >> >> if (ret) >> SetPageError(page) >> // miss clearing the writeback bit >> >> sync() >> ... >> filemap_fdatawait_range() >> wait_on_page_writeback(page); >> // wait the false under-writeback page >> >> Signed-off-by: Takafumi Kubota <takafumi.kubota1012@sslab.ics.keio.ac.jp> >> --- >> fs/btrfs/extent_io.c | 4 +++- >> 1 file changed, 3 insertions(+), 1 deletion(-) >> >> diff --git a/fs/btrfs/extent_io.c b/fs/btrfs/extent_io.c >> index 1e67723..ef9793b 100644 >> --- a/fs/btrfs/extent_io.c >> +++ b/fs/btrfs/extent_io.c >> @@ -3443,8 +3443,10 @@ static noinline_for_stack int __extent_writepage_io(struct inode *inode, >> bdev, &epd->bio, max_nr, >> end_bio_extent_writepage, >> 0, 0, 0, false); >> - if (ret) >> + if (ret) { >> SetPageError(page); >> + end_page_writeback(page); >> + } > OK...this could be complex as we don't know which part in > submit_extent_page gets the error, if the page has been added into bio > and bio_end would call end_page_writepage(page) as well, so whichever > comes later, the BUG() in end_page_writeback() would complain. > > Looks like commit 55e3bd2e0c2e1 also has the same problem although I > gave it my reviewed-by. > > Thanks, > > -liubo > >> >> cur = cur + iosize; >> pg_offset += iosize; >> -- >> 1.9.3 >> >> -- >> To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in >> the body of a message to majordomo@vger.kernel.org >> More majordomo info at http://vger.kernel.org/majordomo-info.html
On Fri, Jan 13, 2017 at 03:12:31PM +0900, takafumi-sslab wrote: > Thanks for your replying. > > I understand this bug is more complicated than I expected. > I classify error cases under submit_extent_page() below > > A: ENOMEM error at btrfs_bio_alloc() in submit_extent_page() > I first assumed this case and sent the mail. > When bio_ret is NULL, submit_extent_page() calls btrfs_bio_alloc(). > Then, btrfs_bio_alloc() may fail and submit_extent_page() returns -ENOMEM. > In this case, bio_endio() is not called and the page's writeback bit > remains. > So, there is a need to call end_page_writeback() in the error handling. > > B: errors under submit_one_bio() of submit_extent_page() > Errors that occur under submit_one_bio() handles at bio_endio(), and > bio_endio() would call end_page_writeback(). > > Therefore, as you mentioned in the last mail, simply adding > end_page_writeback() like my last email and commit 55e3bd2e0c2e1 can > conflict in the case of B. > To avoid such conflict, one easy solution is adding PageWriteback() check > too. > > How do you think of this solution? (sorry for the late reply.) I think its caller, "__extent_writepage", has covered the above case by setting page writeback again. Thanks, -liubo > > Sincerely, > > On 2016/12/22 15:20, Liu Bo wrote: > > On Fri, Dec 16, 2016 at 03:41:50PM +0900, Takafumi Kubota wrote: > > > This is actually inspired by Filipe's patch(55e3bd2e0c2e1). > > > > > > When submit_extent_page() in __extent_writepage_io() fails, > > > Btrfs misses clearing a writeback bit of the failed page. > > > This causes the false under-writeback page. > > > Then, another sync task hangs in filemap_fdatawait_range(), > > > because it waits the false under-writeback page. > > > > > > CPU0 CPU1 > > > > > > __extent_writepage_io() > > > ret = submit_extent_page() // fail > > > > > > if (ret) > > > SetPageError(page) > > > // miss clearing the writeback bit > > > > > > sync() > > > ... > > > filemap_fdatawait_range() > > > wait_on_page_writeback(page); > > > // wait the false under-writeback page > > > > > > Signed-off-by: Takafumi Kubota <takafumi.kubota1012@sslab.ics.keio.ac.jp> > > > --- > > > fs/btrfs/extent_io.c | 4 +++- > > > 1 file changed, 3 insertions(+), 1 deletion(-) > > > > > > diff --git a/fs/btrfs/extent_io.c b/fs/btrfs/extent_io.c > > > index 1e67723..ef9793b 100644 > > > --- a/fs/btrfs/extent_io.c > > > +++ b/fs/btrfs/extent_io.c > > > @@ -3443,8 +3443,10 @@ static noinline_for_stack int __extent_writepage_io(struct inode *inode, > > > bdev->bio, max_nr, > > > end_bio_extent_writepage, > > > 0, 0, 0, false); > > > - if (ret) > > > + if (ret) { > > > SetPageError(page); > > > + end_page_writeback(page); > > > + } > > OK...this could be complex as we don't know which part in > > submit_extent_page gets the error, if the page has been added into bio > > and bio_end would call end_page_writepage(page) as well, so whichever > > comes later, the BUG() in end_page_writeback() would complain. > > > > Looks like commit 55e3bd2e0c2e1 also has the same problem although I > > gave it my reviewed-by. > > > > Thanks, > > > > -liubo > > > > > cur = cur + iosize; > > > pg_offset += iosize; > > > -- > > > 1.9.3 > > > > > > -- > > > To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in > > > the body of a message to majordomo@vger.kernel.org > > > More majordomo info at http://vger.kernel.org/majordomo-info.html > > -- > Keio University > System Software Laboratory > Takafumi Kubota > takafumi.kubota1012@sslab.ics.keio.jp > -- To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Thanks for your reply.
I think you mentioned about the below if-block in __extent_writepage().
if (nr == 0) {
/* make sure the mapping tag for page dirty gets cleared */
set_page_writeback(page);
end_page_writeback(page);
}
However, this if-block only works when nr is 0, and does not work in the
case we indicated.
According to the below codes that we excerpt from
__extent_writepage_io(), nr is incremented even if submit_extent_page()
fails.
Therefore, we should safely clear the writeback bit in the error
handling after the fail of submit_extent_page() call
while (cur <= end) {
...
ret = submit_extent_page(...);
if (ret)
SetPageError(page);
cur = cur + iosize;
pg_offset += iosize;
nr++;
}
done:
*nr_ret = nr; // *nr_ret is nr of __extent_writepage()
Sincerely,
On 2017/01/31 5:09, Liu Bo wrote:
> On Fri, Jan 13, 2017 at 03:12:31PM +0900, takafumi-sslab wrote:
>> Thanks for your replying.
>>
>> I understand this bug is more complicated than I expected.
>> I classify error cases under submit_extent_page() below
>>
>> A: ENOMEM error at btrfs_bio_alloc() in submit_extent_page()
>> I first assumed this case and sent the mail.
>> When bio_ret is NULL, submit_extent_page() calls btrfs_bio_alloc().
>> Then, btrfs_bio_alloc() may fail and submit_extent_page() returns -ENOMEM.
>> In this case, bio_endio() is not called and the page's writeback bit
>> remains.
>> So, there is a need to call end_page_writeback() in the error handling.
>>
>> B: errors under submit_one_bio() of submit_extent_page()
>> Errors that occur under submit_one_bio() handles at bio_endio(), and
>> bio_endio() would call end_page_writeback().
>>
>> Therefore, as you mentioned in the last mail, simply adding
>> end_page_writeback() like my last email and commit 55e3bd2e0c2e1 can
>> conflict in the case of B.
>> To avoid such conflict, one easy solution is adding PageWriteback() check
>> too.
>>
>> How do you think of this solution?
> (sorry for the late reply.)
>
> I think its caller, "__extent_writepage", has covered the above case
> by setting page writeback again.
>
> Thanks,
>
> -liubo
>> Sincerely,
>>
>> On 2016/12/22 15:20, Liu Bo wrote:
>>> On Fri, Dec 16, 2016 at 03:41:50PM +0900, Takafumi Kubota wrote:
>>>> This is actually inspired by Filipe's patch(55e3bd2e0c2e1).
>>>>
>>>> When submit_extent_page() in __extent_writepage_io() fails,
>>>> Btrfs misses clearing a writeback bit of the failed page.
>>>> This causes the false under-writeback page.
>>>> Then, another sync task hangs in filemap_fdatawait_range(),
>>>> because it waits the false under-writeback page.
>>>>
>>>> CPU0 CPU1
>>>>
>>>> __extent_writepage_io()
>>>> ret = submit_extent_page() // fail
>>>>
>>>> if (ret)
>>>> SetPageError(page)
>>>> // miss clearing the writeback bit
>>>>
>>>> sync()
>>>> ...
>>>> filemap_fdatawait_range()
>>>> wait_on_page_writeback(page);
>>>> // wait the false under-writeback page
>>>>
>>>> Signed-off-by: Takafumi Kubota <takafumi.kubota1012@sslab.ics.keio.ac.jp>
>>>> ---
>>>> fs/btrfs/extent_io.c | 4 +++-
>>>> 1 file changed, 3 insertions(+), 1 deletion(-)
>>>>
>>>> diff --git a/fs/btrfs/extent_io.c b/fs/btrfs/extent_io.c
>>>> index 1e67723..ef9793b 100644
>>>> --- a/fs/btrfs/extent_io.c
>>>> +++ b/fs/btrfs/extent_io.c
>>>> @@ -3443,8 +3443,10 @@ static noinline_for_stack int __extent_writepage_io(struct inode *inode,
>>>> bdev->bio, max_nr,
>>>> end_bio_extent_writepage,
>>>> 0, 0, 0, false);
>>>> - if (ret)
>>>> + if (ret) {
>>>> SetPageError(page);
>>>> + end_page_writeback(page);
>>>> + }
>>> OK...this could be complex as we don't know which part in
>>> submit_extent_page gets the error, if the page has been added into bio
>>> and bio_end would call end_page_writepage(page) as well, so whichever
>>> comes later, the BUG() in end_page_writeback() would complain.
>>>
>>> Looks like commit 55e3bd2e0c2e1 also has the same problem although I
>>> gave it my reviewed-by.
>>>
>>> Thanks,
>>>
>>> -liubo
>>>
>>>> cur = cur + iosize;
>>>> pg_offset += iosize;
>>>> --
>>>> 1.9.3
>>>>
>>>> --
>>>> To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in
>>>> the body of a message to majordomo@vger.kernel.org
>>>> More majordomo info at http://vger.kernel.org/majordomo-info.html
>> --
>> Keio University
>> System Software Laboratory
>> Takafumi Kubota
>> takafumi.kubota1012@sslab.ics.keio.jp
>>
On Wed, Feb 01, 2017 at 12:27:24PM +0900, takafumi-sslab wrote: > Thanks for your reply. > > I think you mentioned about the below if-block in __extent_writepage(). > > if (nr == 0) { > /* make sure the mapping tag for page dirty gets cleared */ > set_page_writeback(page); > end_page_writeback(page); > } Right. > > However, this if-block only works when nr is 0, and does not work in the > case we indicated. > According to the below codes that we excerpt from __extent_writepage_io(), > nr is incremented even if submit_extent_page() fails. > Therefore, we should safely clear the writeback bit in the error handling > after the fail of submit_extent_page() call > > while (cur <= end) { > ... > ret = submit_extent_page(...); > if (ret) > SetPageError(page); > > cur = cur + iosize; > pg_offset += iosize; > nr++; > } > done: > *nr_ret = nr; // *nr_ret is nr of __extent_writepage() It'd be either nr == 0 or nr == 1, right now (nr > 1) couldn't happen on btrfs because it assumes blocksize == PAGE_SIZE, so we could only submit_extent_page once for each page, and bio_ret is used to batch bio submit. (But it could be changed after subpagesize block patchset, and there is more work rather than just adding a end_page_writeback, e.g. writepage endio also needs to be updated). Thanks, -liubo > > Sincerely, > > On 2017/01/31 5:09, Liu Bo wrote: > > On Fri, Jan 13, 2017 at 03:12:31PM +0900, takafumi-sslab wrote: > > > Thanks for your replying. > > > > > > I understand this bug is more complicated than I expected. > > > I classify error cases under submit_extent_page() below > > > > > > A: ENOMEM error at btrfs_bio_alloc() in submit_extent_page() > > > I first assumed this case and sent the mail. > > > When bio_ret is NULL, submit_extent_page() calls btrfs_bio_alloc(). > > > Then, btrfs_bio_alloc() may fail and submit_extent_page() returns -ENOMEM. > > > In this case, bio_endio() is not called and the page's writeback bit > > > remains. > > > So, there is a need to call end_page_writeback() in the error handling. > > > > > > B: errors under submit_one_bio() of submit_extent_page() > > > Errors that occur under submit_one_bio() handles at bio_endio(), and > > > bio_endio() would call end_page_writeback(). > > > > > > Therefore, as you mentioned in the last mail, simply adding > > > end_page_writeback() like my last email and commit 55e3bd2e0c2e1 can > > > conflict in the case of B. > > > To avoid such conflict, one easy solution is adding PageWriteback() check > > > too. > > > > > > How do you think of this solution? > > (sorry for the late reply.) > > > > I think its caller, "__extent_writepage", has covered the above case > > by setting page writeback again. > > > > Thanks, > > > > -liubo > > > Sincerely, > > > > > > On 2016/12/22 15:20, Liu Bo wrote: > > > > On Fri, Dec 16, 2016 at 03:41:50PM +0900, Takafumi Kubota wrote: > > > > > This is actually inspired by Filipe's patch(55e3bd2e0c2e1). > > > > > > > > > > When submit_extent_page() in __extent_writepage_io() fails, > > > > > Btrfs misses clearing a writeback bit of the failed page. > > > > > This causes the false under-writeback page. > > > > > Then, another sync task hangs in filemap_fdatawait_range(), > > > > > because it waits the false under-writeback page. > > > > > > > > > > CPU0 CPU1 > > > > > > > > > > __extent_writepage_io() > > > > > ret = submit_extent_page() // fail > > > > > > > > > > if (ret) > > > > > SetPageError(page) > > > > > // miss clearing the writeback bit > > > > > > > > > > sync() > > > > > ... > > > > > filemap_fdatawait_range() > > > > > wait_on_page_writeback(page); > > > > > // wait the false under-writeback page > > > > > > > > > > Signed-off-by: Takafumi Kubota <takafumi.kubota1012@sslab.ics.keio.ac.jp> > > > > > --- > > > > > fs/btrfs/extent_io.c | 4 +++- > > > > > 1 file changed, 3 insertions(+), 1 deletion(-) > > > > > > > > > > diff --git a/fs/btrfs/extent_io.c b/fs/btrfs/extent_io.c > > > > > index 1e67723..ef9793b 100644 > > > > > --- a/fs/btrfs/extent_io.c > > > > > +++ b/fs/btrfs/extent_io.c > > > > > @@ -3443,8 +3443,10 @@ static noinline_for_stack int __extent_writepage_io(struct inode *inode, > > > > > bdev->bio, max_nr, > > > > > end_bio_extent_writepage, > > > > > 0, 0, 0, false); > > > > > - if (ret) > > > > > + if (ret) { > > > > > SetPageError(page); > > > > > + end_page_writeback(page); > > > > > + } > > > > OK...this could be complex as we don't know which part in > > > > submit_extent_page gets the error, if the page has been added into bio > > > > and bio_end would call end_page_writepage(page) as well, so whichever > > > > comes later, the BUG() in end_page_writeback() would complain. > > > > > > > > Looks like commit 55e3bd2e0c2e1 also has the same problem although I > > > > gave it my reviewed-by. > > > > > > > > Thanks, > > > > > > > > -liubo > > > > > > > > > cur = cur + iosize; > > > > > pg_offset += iosize; > > > > > -- > > > > > 1.9.3 > > > > > > > > > > -- > > > > > To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in > > > > > the body of a message to majordomo@vger.kernel.org > > > > > More majordomo info at http://vger.kernel.org/majordomo-info.html > > > -- > > > Keio University > > > System Software Laboratory > > > Takafumi Kubota > > > takafumi.kubota1012@sslab.ics.keio.jp > > > > > -- > Keio University > System Software Laboratory > Takafumi Kubota > takafumi.kubota1012@sslab.ics.keio.jp > -- To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
> (But it could be changed after subpagesize block patchset, and there is > more work rather than just adding a end_page_writeback, e.g. writepage > endio also needs to be updated). Ok... the discussion become complicated. So, let me make this clear. you think a) this is a bug; we need to clear the writeback bit in the error handling if the bit remains. b) however, the way of fixing this bug has some concerns. ( and now we discuss the best solution ) Is my understanding correct? Sincerely, -takafumi > > Thanks, > > -liubo >> Sincerely, >> >> On 2017/01/31 5:09, Liu Bo wrote: >>> On Fri, Jan 13, 2017 at 03:12:31PM +0900, takafumi-sslab wrote: >>>> Thanks for your replying. >>>> >>>> I understand this bug is more complicated than I expected. >>>> I classify error cases under submit_extent_page() below >>>> >>>> A: ENOMEM error at btrfs_bio_alloc() in submit_extent_page() >>>> I first assumed this case and sent the mail. >>>> When bio_ret is NULL, submit_extent_page() calls btrfs_bio_alloc(). >>>> Then, btrfs_bio_alloc() may fail and submit_extent_page() returns -ENOMEM. >>>> In this case, bio_endio() is not called and the page's writeback bit >>>> remains. >>>> So, there is a need to call end_page_writeback() in the error handling. >>>> >>>> B: errors under submit_one_bio() of submit_extent_page() >>>> Errors that occur under submit_one_bio() handles at bio_endio(), and >>>> bio_endio() would call end_page_writeback(). >>>> >>>> Therefore, as you mentioned in the last mail, simply adding >>>> end_page_writeback() like my last email and commit 55e3bd2e0c2e1 can >>>> conflict in the case of B. >>>> To avoid such conflict, one easy solution is adding PageWriteback() check >>>> too. >>>> >>>> How do you think of this solution? >>> (sorry for the late reply.) >>> >>> I think its caller, "__extent_writepage", has covered the above case >>> by setting page writeback again. >>> >>> Thanks, >>> >>> -liubo >>>> Sincerely, >>>> >>>> On 2016/12/22 15:20, Liu Bo wrote: >>>>> On Fri, Dec 16, 2016 at 03:41:50PM +0900, Takafumi Kubota wrote: >>>>>> This is actually inspired by Filipe's patch(55e3bd2e0c2e1). >>>>>> >>>>>> When submit_extent_page() in __extent_writepage_io() fails, >>>>>> Btrfs misses clearing a writeback bit of the failed page. >>>>>> This causes the false under-writeback page. >>>>>> Then, another sync task hangs in filemap_fdatawait_range(), >>>>>> because it waits the false under-writeback page. >>>>>> >>>>>> CPU0 CPU1 >>>>>> >>>>>> __extent_writepage_io() >>>>>> ret = submit_extent_page() // fail >>>>>> >>>>>> if (ret) >>>>>> SetPageError(page) >>>>>> // miss clearing the writeback bit >>>>>> >>>>>> sync() >>>>>> ... >>>>>> filemap_fdatawait_range() >>>>>> wait_on_page_writeback(page); >>>>>> // wait the false under-writeback page >>>>>> >>>>>> Signed-off-by: Takafumi Kubota <takafumi.kubota1012@sslab.ics.keio.ac.jp> >>>>>> --- >>>>>> fs/btrfs/extent_io.c | 4 +++- >>>>>> 1 file changed, 3 insertions(+), 1 deletion(-) >>>>>> >>>>>> diff --git a/fs/btrfs/extent_io.c b/fs/btrfs/extent_io.c >>>>>> index 1e67723..ef9793b 100644 >>>>>> --- a/fs/btrfs/extent_io.c >>>>>> +++ b/fs/btrfs/extent_io.c >>>>>> @@ -3443,8 +3443,10 @@ static noinline_for_stack int __extent_writepage_io(struct inode *inode, >>>>>> bdev->bio, max_nr, >>>>>> end_bio_extent_writepage, >>>>>> 0, 0, 0, false); >>>>>> - if (ret) >>>>>> + if (ret) { >>>>>> SetPageError(page); >>>>>> + end_page_writeback(page); >>>>>> + } >>>>> OK...this could be complex as we don't know which part in >>>>> submit_extent_page gets the error, if the page has been added into bio >>>>> and bio_end would call end_page_writepage(page) as well, so whichever >>>>> comes later, the BUG() in end_page_writeback() would complain. >>>>> >>>>> Looks like commit 55e3bd2e0c2e1 also has the same problem although I >>>>> gave it my reviewed-by. >>>>> >>>>> Thanks, >>>>> >>>>> -liubo >>>>> >>>>>> cur = cur + iosize; >>>>>> pg_offset += iosize; >>>>>> -- >>>>>> 1.9.3 >>>>>> >>>>>> -- >>>>>> To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in >>>>>> the body of a message to majordomo@vger.kernel.org >>>>>> More majordomo info at http://vger.kernel.org/majordomo-info.html >>>> -- >>>> Keio University >>>> System Software Laboratory >>>> Takafumi Kubota >>>> takafumi.kubota1012@sslab.ics.keio.jp >>>> >> -- >> Keio University >> System Software Laboratory >> Takafumi Kubota >> takafumi.kubota1012@sslab.ics.keio.jp >>
On Sat, Feb 04, 2017 at 09:42:17PM +0900, takafumi-sslab wrote: > > > (But it could be changed after subpagesize block patchset, and there is > > more work rather than just adding a end_page_writeback, e.g. writepage > > endio also needs to be updated). > > Ok... the discussion become complicated. > So, let me make this clear. > > you think > a) this is a bug; > we need to clear the writeback bit in the error handling if the bit remains. > > b) however, the way of fixing this bug has some concerns. ( and now we > discuss the best solution ) > > Is my understanding correct? Sorry for making you confused even more, to clarify it, I don't think the bug could exist in the current btrfs because blocksize is equal to PAGE_SIZE so that @nr in __extent_writepage could only be 0 or 1. a) __extent_writepage has handled the case when nr == 0. b) when nr == 1, the page is marked with writeback bit and added into a bio, thus we have bio_end to deal with page bits. So I don't think the patch is necessary for now. But as I said, the fact (nr == 0 or 1) would be changed if the subpagesize blocksize is supported. Thanks, -liubo > > Sincerely, > > -takafumi > > > > Thanks, > > > > -liubo > > > Sincerely, > > > > > > On 2017/01/31 5:09, Liu Bo wrote: > > > > On Fri, Jan 13, 2017 at 03:12:31PM +0900, takafumi-sslab wrote: > > > > > Thanks for your replying. > > > > > > > > > > I understand this bug is more complicated than I expected. > > > > > I classify error cases under submit_extent_page() below > > > > > > > > > > A: ENOMEM error at btrfs_bio_alloc() in submit_extent_page() > > > > > I first assumed this case and sent the mail. > > > > > When bio_ret is NULL, submit_extent_page() calls btrfs_bio_alloc(). > > > > > Then, btrfs_bio_alloc() may fail and submit_extent_page() returns -ENOMEM. > > > > > In this case, bio_endio() is not called and the page's writeback bit > > > > > remains. > > > > > So, there is a need to call end_page_writeback() in the error handling. > > > > > > > > > > B: errors under submit_one_bio() of submit_extent_page() > > > > > Errors that occur under submit_one_bio() handles at bio_endio(), and > > > > > bio_endio() would call end_page_writeback(). > > > > > > > > > > Therefore, as you mentioned in the last mail, simply adding > > > > > end_page_writeback() like my last email and commit 55e3bd2e0c2e1 can > > > > > conflict in the case of B. > > > > > To avoid such conflict, one easy solution is adding PageWriteback() check > > > > > too. > > > > > > > > > > How do you think of this solution? > > > > (sorry for the late reply.) > > > > > > > > I think its caller, "__extent_writepage", has covered the above case > > > > by setting page writeback again. > > > > > > > > Thanks, > > > > > > > > -liubo > > > > > Sincerely, > > > > > > > > > > On 2016/12/22 15:20, Liu Bo wrote: > > > > > > On Fri, Dec 16, 2016 at 03:41:50PM +0900, Takafumi Kubota wrote: > > > > > > > This is actually inspired by Filipe's patch(55e3bd2e0c2e1). > > > > > > > > > > > > > > When submit_extent_page() in __extent_writepage_io() fails, > > > > > > > Btrfs misses clearing a writeback bit of the failed page. > > > > > > > This causes the false under-writeback page. > > > > > > > Then, another sync task hangs in filemap_fdatawait_range(), > > > > > > > because it waits the false under-writeback page. > > > > > > > > > > > > > > CPU0 CPU1 > > > > > > > > > > > > > > __extent_writepage_io() > > > > > > > ret = submit_extent_page() // fail > > > > > > > > > > > > > > if (ret) > > > > > > > SetPageError(page) > > > > > > > // miss clearing the writeback bit > > > > > > > > > > > > > > sync() > > > > > > > ... > > > > > > > filemap_fdatawait_range() > > > > > > > wait_on_page_writeback(page); > > > > > > > // wait the false under-writeback page > > > > > > > > > > > > > > Signed-off-by: Takafumi Kubota <takafumi.kubota1012@sslab.ics.keio.ac.jp> > > > > > > > --- > > > > > > > fs/btrfs/extent_io.c | 4 +++- > > > > > > > 1 file changed, 3 insertions(+), 1 deletion(-) > > > > > > > > > > > > > > diff --git a/fs/btrfs/extent_io.c b/fs/btrfs/extent_io.c > > > > > > > index 1e67723..ef9793b 100644 > > > > > > > --- a/fs/btrfs/extent_io.c > > > > > > > +++ b/fs/btrfs/extent_io.c > > > > > > > @@ -3443,8 +3443,10 @@ static noinline_for_stack int __extent_writepage_io(struct inode *inode, > > > > > > > bdev->bio, max_nr, > > > > > > > end_bio_extent_writepage, > > > > > > > 0, 0, 0, false); > > > > > > > - if (ret) > > > > > > > + if (ret) { > > > > > > > SetPageError(page); > > > > > > > + end_page_writeback(page); > > > > > > > + } > > > > > > OK...this could be complex as we don't know which part in > > > > > > submit_extent_page gets the error, if the page has been added into bio > > > > > > and bio_end would call end_page_writepage(page) as well, so whichever > > > > > > comes later, the BUG() in end_page_writeback() would complain. > > > > > > > > > > > > Looks like commit 55e3bd2e0c2e1 also has the same problem although I > > > > > > gave it my reviewed-by. > > > > > > > > > > > > Thanks, > > > > > > > > > > > > -liubo > > > > > > > > > > > > > cur = cur + iosize; > > > > > > > pg_offset += iosize; > > > > > > > -- > > > > > > > 1.9.3 > > > > > > > > > > > > > > -- > > > > > > > To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in > > > > > > > the body of a message to majordomo@vger.kernel.org > > > > > > > More majordomo info at http://vger.kernel.org/majordomo-info.html > > > > > -- > > > > > Keio University > > > > > System Software Laboratory > > > > > Takafumi Kubota > > > > > takafumi.kubota1012@sslab.ics.keio.jp > > > > > > > > -- > > > Keio University > > > System Software Laboratory > > > Takafumi Kubota > > > takafumi.kubota1012@sslab.ics.keio.jp > > > > > -- > Keio University > System Software Laboratory > Takafumi Kubota > takafumi.kubota1012@sslab.ics.keio.jp > -- To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
On 2017/02/06 12:35, Liu Bo wrote: > a) __extent_writepage has handled the case when nr == 0. Yes, I agree this. > b) when nr == 1, the page is marked with writeback bit and added into a > bio, thus we have bio_end to deal with page bits. However, I don't think this is always correct, because, as I said before as the Error A, when (bio_ret == NULL or *bio_ret == NULL) and btrfs_bio_alloc() fails, the page is not added into a bio. Thus, bio_end does not deal with the page's bit, and the writeback bit remains with nr == 1. To confirm this, I inject a fault to mimic the fail of btrfs_bio_alloc(). I can reproduce the hang at the kernel ver4.10-rc7 that commit id is d5adbfcd5f7bcc6fa58a41c5c5ada0e5c826ce2c and Ftrace log messages are like below a.out-2867 : __extent_writepage: call __extent_writepage_io: page:0xffffea000006d200(writeback:0), nr:0, logged at just previous to line 3523 of extent_io.c a.out-2867 : __extent_writepage_io: call submit_extent_page: page:0xffffea000006d200(writeback:1), nr:0, bio_ret:0xffffc90003bd7d40, *bio_ret: (null), logged at just previous to line 3443 of extent_io.c a.out-2867 : submit_extent_page.isra.53: Mimic Error A: btrfs_bio_alloc() fails and submit_extent_page() return -ENOMEM, logged at just previous to line 2807 of extent_io.c a.out-2867 : __extent_writepage_io: after call submit_extent_page: page:0xffffea000006d200(writeback:1), nr:0, bio_ret:0xffffc90003bd7d40, *bio_ret: (null), logged at just next to line 3447 of extent_io.c a.out-2867 : __extent_writepage_io: nr == 1: page:0xffffea000006d200(writeback:1), nr:1, bio_ret:0xffffc90003de7d40, logged at just next to line 3456 of extent_io.c //nr == 1 and the writeback bit remains a.out-2867 : __extent_writepage: after call __extent_writepage_io: page:0xffffea000006d200(writeback:1), nr:1, logged at just next to line 3524 of extent_io.c // __extent_writepage does not handle, because nr == 1 ... sync-2868 : __filemap_fdatawait_range: wait_on_page_writeback: page:0xffffea000006d200, logged at just previous to line 404 of mm/filemap.c // Then, sync hangs Sincerely, -takafumi > > So I don't think the patch is necessary for now. > > But as I said, the fact (nr == 0 or 1) would be changed if the > subpagesize blocksize is supported. > > Thanks, > > -liubo > >> Sincerely, >> >> -takafumi >>> Thanks, >>> >>> -liubo >>>> Sincerely, >>>> >>>> On 2017/01/31 5:09, Liu Bo wrote: >>>>> On Fri, Jan 13, 2017 at 03:12:31PM +0900, takafumi-sslab wrote: >>>>>> Thanks for your replying. >>>>>> >>>>>> I understand this bug is more complicated than I expected. >>>>>> I classify error cases under submit_extent_page() below >>>>>> >>>>>> A: ENOMEM error at btrfs_bio_alloc() in submit_extent_page() >>>>>> I first assumed this case and sent the mail. >>>>>> When bio_ret is NULL, submit_extent_page() calls btrfs_bio_alloc(). >>>>>> Then, btrfs_bio_alloc() may fail and submit_extent_page() returns -ENOMEM. >>>>>> In this case, bio_endio() is not called and the page's writeback bit >>>>>> remains. >>>>>> So, there is a need to call end_page_writeback() in the error handling. >>>>>> >>>>>> B: errors under submit_one_bio() of submit_extent_page() >>>>>> Errors that occur under submit_one_bio() handles at bio_endio(), and >>>>>> bio_endio() would call end_page_writeback(). >>>>>> >>>>>> Therefore, as you mentioned in the last mail, simply adding >>>>>> end_page_writeback() like my last email and commit 55e3bd2e0c2e1 can >>>>>> conflict in the case of B. >>>>>> To avoid such conflict, one easy solution is adding PageWriteback() check >>>>>> too. >>>>>> >>>>>> How do you think of this solution? >>>>> (sorry for the late reply.) >>>>> >>>>> I think its caller, "__extent_writepage", has covered the above case >>>>> by setting page writeback again. >>>>> >>>>> Thanks, >>>>> >>>>> -liubo >>>>>> Sincerely, >>>>>> >>>>>> On 2016/12/22 15:20, Liu Bo wrote: >>>>>>> On Fri, Dec 16, 2016 at 03:41:50PM +0900, Takafumi Kubota wrote: >>>>>>>> This is actually inspired by Filipe's patch(55e3bd2e0c2e1). >>>>>>>> >>>>>>>> When submit_extent_page() in __extent_writepage_io() fails, >>>>>>>> Btrfs misses clearing a writeback bit of the failed page. >>>>>>>> This causes the false under-writeback page. >>>>>>>> Then, another sync task hangs in filemap_fdatawait_range(), >>>>>>>> because it waits the false under-writeback page. >>>>>>>> >>>>>>>> CPU0 CPU1 >>>>>>>> >>>>>>>> __extent_writepage_io() >>>>>>>> ret = submit_extent_page() // fail >>>>>>>> >>>>>>>> if (ret) >>>>>>>> SetPageError(page) >>>>>>>> // miss clearing the writeback bit >>>>>>>> >>>>>>>> sync() >>>>>>>> ... >>>>>>>> filemap_fdatawait_range() >>>>>>>> wait_on_page_writeback(page); >>>>>>>> // wait the false under-writeback page >>>>>>>> >>>>>>>> Signed-off-by: Takafumi Kubota <takafumi.kubota1012@sslab.ics.keio.ac.jp> >>>>>>>> --- >>>>>>>> fs/btrfs/extent_io.c | 4 +++- >>>>>>>> 1 file changed, 3 insertions(+), 1 deletion(-) >>>>>>>> >>>>>>>> diff --git a/fs/btrfs/extent_io.c b/fs/btrfs/extent_io.c >>>>>>>> index 1e67723..ef9793b 100644 >>>>>>>> --- a/fs/btrfs/extent_io.c >>>>>>>> +++ b/fs/btrfs/extent_io.c >>>>>>>> @@ -3443,8 +3443,10 @@ static noinline_for_stack int __extent_writepage_io(struct inode *inode, >>>>>>>> bdev->bio, max_nr, >>>>>>>> end_bio_extent_writepage, >>>>>>>> 0, 0, 0, false); >>>>>>>> - if (ret) >>>>>>>> + if (ret) { >>>>>>>> SetPageError(page); >>>>>>>> + end_page_writeback(page); >>>>>>>> + } >>>>>>> OK...this could be complex as we don't know which part in >>>>>>> submit_extent_page gets the error, if the page has been added into bio >>>>>>> and bio_end would call end_page_writepage(page) as well, so whichever >>>>>>> comes later, the BUG() in end_page_writeback() would complain. >>>>>>> >>>>>>> Looks like commit 55e3bd2e0c2e1 also has the same problem although I >>>>>>> gave it my reviewed-by. >>>>>>> >>>>>>> Thanks, >>>>>>> >>>>>>> -liubo >>>>>>> >>>>>>>> cur = cur + iosize; >>>>>>>> pg_offset += iosize; >>>>>>>> -- >>>>>>>> 1.9.3 >>>>>>>> >>>>>>>> -- >>>>>>>> To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in >>>>>>>> the body of a message to majordomo@vger.kernel.org >>>>>>>> More majordomo info at http://vger.kernel.org/majordomo-info.html >>>>>> -- >>>>>> Keio University >>>>>> System Software Laboratory >>>>>> Takafumi Kubota >>>>>> takafumi.kubota1012@sslab.ics.keio.jp >>>>>> >>>> -- >>>> Keio University >>>> System Software Laboratory >>>> Takafumi Kubota >>>> takafumi.kubota1012@sslab.ics.keio.jp >>>> >> -- >> Keio University >> System Software Laboratory >> Takafumi Kubota >> takafumi.kubota1012@sslab.ics.keio.jp >>
I am sorry for forggeting to write the reproducing steps.
I injects the ftrace's logging code and the fault to the Linux kerenl
v4.10-rc7.
The diff is too long for pasting here.
So, I put the repository of the kernel here.
https://github.com/tk1012/linux-for-reproduce-btrfs-failure.git
And the steps to reproduce are:
$ git clone https://github.com/tk1012/linux-for-reproduce-btrfs-failure.git
$ make menuconfig # enable these configs
- CONFIG_FAILSLAB
- CONFIG_FAULT_INJECTION_DEBUG_FS
- CONFIG_FTRACE
$ make && make install
Then, I run the below reproducer.
And, you can see the ftrace log like:
$ cat /sys/kernel/debug/tracing/trace > ~/ftrace_log
FYI, you can use the kernel config here.
https://github.com/tk1012/linux-for-reproduce-btrfs-failure/blob/master/minconfig
----------
#!/bin/bash
set -xe
echo 128000 > /sys/kernel/debug/tracing/buffer_size_kb
echo N > /sys/kernel/debug/failk9/task-filter
echo N > /sys/kernel/debug/failk9/ignore-gfp-wait
echo 100 > /sys/kernel/debug/failk9/probability
echo 1 > /sys/kernel/debug/failk9/interval
directory=/mnt/btrfs
mkdir -p ${directory}
truncate -s 100G btrfs.img
mkfs.btrfs btrfs.img
mount btrfs.img ${directory}
for i in `seq 1 1 100`; do
echo 1 > /sys/kernel/debug/failk9/times
bash -c "echo 1 > /proc/self/make-it-fail && dd if=/dev/zero
of=${directory}/text_txt bs=1M count=10 2> /dev/null"
sync # never return
done
umount ${directory}
----------
Sincerely,
-takafumi
On 2017/02/06 12:35, Liu Bo wrote:
> On Sat, Feb 04, 2017 at 09:42:17PM +0900, takafumi-sslab wrote:
>>
>>> (But it could be changed after subpagesize block patchset, and there is
>>> more work rather than just adding a end_page_writeback, e.g. writepage
>>> endio also needs to be updated).
>>
>> Ok... the discussion become complicated.
>> So, let me make this clear.
>>
>> you think
>> a) this is a bug;
>> we need to clear the writeback bit in the error handling if the bit remains.
>>
>> b) however, the way of fixing this bug has some concerns. ( and now we
>> discuss the best solution )
>>
>> Is my understanding correct?
>
> Sorry for making you confused even more, to clarify it, I don't think
> the bug could exist in the current btrfs because blocksize is equal to
> PAGE_SIZE so that @nr in __extent_writepage could only be 0 or 1.
>
> a) __extent_writepage has handled the case when nr == 0.
> b) when nr == 1, the page is marked with writeback bit and added into a
> bio, thus we have bio_end to deal with page bits.
>
> So I don't think the patch is necessary for now.
>
> But as I said, the fact (nr == 0 or 1) would be changed if the
> subpagesize blocksize is supported.
>
> Thanks,
>
> -liubo
>
>>
>> Sincerely,
>>
>> -takafumi
>>>
>>> Thanks,
>>>
>>> -liubo
>>>> Sincerely,
>>>>
>>>> On 2017/01/31 5:09, Liu Bo wrote:
>>>>> On Fri, Jan 13, 2017 at 03:12:31PM +0900, takafumi-sslab wrote:
>>>>>> Thanks for your replying.
>>>>>>
>>>>>> I understand this bug is more complicated than I expected.
>>>>>> I classify error cases under submit_extent_page() below
>>>>>>
>>>>>> A: ENOMEM error at btrfs_bio_alloc() in submit_extent_page()
>>>>>> I first assumed this case and sent the mail.
>>>>>> When bio_ret is NULL, submit_extent_page() calls btrfs_bio_alloc().
>>>>>> Then, btrfs_bio_alloc() may fail and submit_extent_page() returns -ENOMEM.
>>>>>> In this case, bio_endio() is not called and the page's writeback bit
>>>>>> remains.
>>>>>> So, there is a need to call end_page_writeback() in the error handling.
>>>>>>
>>>>>> B: errors under submit_one_bio() of submit_extent_page()
>>>>>> Errors that occur under submit_one_bio() handles at bio_endio(), and
>>>>>> bio_endio() would call end_page_writeback().
>>>>>>
>>>>>> Therefore, as you mentioned in the last mail, simply adding
>>>>>> end_page_writeback() like my last email and commit 55e3bd2e0c2e1 can
>>>>>> conflict in the case of B.
>>>>>> To avoid such conflict, one easy solution is adding PageWriteback() check
>>>>>> too.
>>>>>>
>>>>>> How do you think of this solution?
>>>>> (sorry for the late reply.)
>>>>>
>>>>> I think its caller, "__extent_writepage", has covered the above case
>>>>> by setting page writeback again.
>>>>>
>>>>> Thanks,
>>>>>
>>>>> -liubo
>>>>>> Sincerely,
>>>>>>
>>>>>> On 2016/12/22 15:20, Liu Bo wrote:
>>>>>>> On Fri, Dec 16, 2016 at 03:41:50PM +0900, Takafumi Kubota wrote:
>>>>>>>> This is actually inspired by Filipe's patch(55e3bd2e0c2e1).
>>>>>>>>
>>>>>>>> When submit_extent_page() in __extent_writepage_io() fails,
>>>>>>>> Btrfs misses clearing a writeback bit of the failed page.
>>>>>>>> This causes the false under-writeback page.
>>>>>>>> Then, another sync task hangs in filemap_fdatawait_range(),
>>>>>>>> because it waits the false under-writeback page.
>>>>>>>>
>>>>>>>> CPU0 CPU1
>>>>>>>>
>>>>>>>> __extent_writepage_io()
>>>>>>>> ret = submit_extent_page() // fail
>>>>>>>>
>>>>>>>> if (ret)
>>>>>>>> SetPageError(page)
>>>>>>>> // miss clearing the writeback bit
>>>>>>>>
>>>>>>>> sync()
>>>>>>>> ...
>>>>>>>> filemap_fdatawait_range()
>>>>>>>> wait_on_page_writeback(page);
>>>>>>>> // wait the false under-writeback page
>>>>>>>>
>>>>>>>> Signed-off-by: Takafumi Kubota <takafumi.kubota1012@sslab.ics.keio.ac.jp>
>>>>>>>> ---
>>>>>>>> fs/btrfs/extent_io.c | 4 +++-
>>>>>>>> 1 file changed, 3 insertions(+), 1 deletion(-)
>>>>>>>>
>>>>>>>> diff --git a/fs/btrfs/extent_io.c b/fs/btrfs/extent_io.c
>>>>>>>> index 1e67723..ef9793b 100644
>>>>>>>> --- a/fs/btrfs/extent_io.c
>>>>>>>> +++ b/fs/btrfs/extent_io.c
>>>>>>>> @@ -3443,8 +3443,10 @@ static noinline_for_stack int __extent_writepage_io(struct inode *inode,
>>>>>>>> bdev->bio, max_nr,
>>>>>>>> end_bio_extent_writepage,
>>>>>>>> 0, 0, 0, false);
>>>>>>>> - if (ret)
>>>>>>>> + if (ret) {
>>>>>>>> SetPageError(page);
>>>>>>>> + end_page_writeback(page);
>>>>>>>> + }
>>>>>>> OK...this could be complex as we don't know which part in
>>>>>>> submit_extent_page gets the error, if the page has been added into bio
>>>>>>> and bio_end would call end_page_writepage(page) as well, so whichever
>>>>>>> comes later, the BUG() in end_page_writeback() would complain.
>>>>>>>
>>>>>>> Looks like commit 55e3bd2e0c2e1 also has the same problem although I
>>>>>>> gave it my reviewed-by.
>>>>>>>
>>>>>>> Thanks,
>>>>>>>
>>>>>>> -liubo
>>>>>>>
>>>>>>>> cur = cur + iosize;
>>>>>>>> pg_offset += iosize;
>>>>>>>> --
>>>>>>>> 1.9.3
>>>>>>>>
>>>>>>>> --
>>>>>>>> To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in
>>>>>>>> the body of a message to majordomo@vger.kernel.org
>>>>>>>> More majordomo info at http://vger.kernel.org/majordomo-info.html
>>>>>> --
>>>>>> Keio University
>>>>>> System Software Laboratory
>>>>>> Takafumi Kubota
>>>>>> takafumi.kubota1012@sslab.ics.keio.jp
>>>>>>
>>>> --
>>>> Keio University
>>>> System Software Laboratory
>>>> Takafumi Kubota
>>>> takafumi.kubota1012@sslab.ics.keio.jp
>>>>
>>
>> --
>> Keio University
>> System Software Laboratory
>> Takafumi Kubota
>> takafumi.kubota1012@sslab.ics.keio.jp
>>
On Mon, Feb 06, 2017 at 02:50:18PM +0900, takafumi-sslab wrote: > > > On 2017/02/06 12:35, Liu Bo wrote: > > a) __extent_writepage has handled the case when nr == 0. > > Yes, I agree this. > > > b) when nr == 1, the page is marked with writeback bit and added into a > > bio, thus we have bio_end to deal with page bits. > > However, I don't think this is always correct, > because, as I said before as the Error A, when (bio_ret == NULL or *bio_ret > == NULL) and btrfs_bio_alloc() fails, the page is not added into a bio. > Thus, bio_end does not deal with the page's bit, and the writeback bit > remains with nr == 1. > > To confirm this, I inject a fault to mimic the fail of btrfs_bio_alloc(). > I can reproduce the hang at the kernel ver4.10-rc7 that commit id is > d5adbfcd5f7bcc6fa58a41c5c5ada0e5c826ce2c > and Ftrace log messages are like below > > a.out-2867 : __extent_writepage: call __extent_writepage_io: > page:0xffffea000006d200(writeback:0), nr:0, logged at just previous to line > 3523 of extent_io.c > a.out-2867 : __extent_writepage_io: call submit_extent_page: > page:0xffffea000006d200(writeback:1), nr:0, bio_ret:0xffffc90003bd7d40, > *bio_ret: (null), logged at just previous to line 3443 of extent_io.c > a.out-2867 : submit_extent_page.isra.53: Mimic Error A: btrfs_bio_alloc() > fails and submit_extent_page() return -ENOMEM, logged at just previous to > line 2807 of extent_io.c > a.out-2867 : __extent_writepage_io: after call submit_extent_page: > page:0xffffea000006d200(writeback:1), nr:0, bio_ret:0xffffc90003bd7d40, > *bio_ret: (null), logged at just next to line 3447 of extent_io.c > a.out-2867 : __extent_writepage_io: nr == 1: > page:0xffffea000006d200(writeback:1), nr:1, bio_ret:0xffffc90003de7d40, > logged at just next to line 3456 of extent_io.c //nr == 1 and the writeback > bit remains > a.out-2867 : __extent_writepage: after call __extent_writepage_io: > page:0xffffea000006d200(writeback:1), nr:1, logged at just next to line 3524 > of extent_io.c // __extent_writepage does not handle, because nr == 1 > ... > sync-2868 : __filemap_fdatawait_range: wait_on_page_writeback: > page:0xffffea000006d200, logged at just previous to line 404 of mm/filemap.c > // Then, sync hangs Thanks for the efforts to prove it, nice. Obviously I missed that @nr will even be bumped up by one if ENOMEM, so yes, we need to clear the writeback bit. But shouldn't @nr means nr_submitted_successfully? If a submit fails, it makes no senses to keep submitting subsequent parts. Anyway, for now I think the proposed fix is good to solve the problem, so you may add Reviewed-by: Liu Bo <bo.li.liu@oracle.com> Thanks, -liubo > > Sincerely, > > -takafumi > > > > So I don't think the patch is necessary for now. > > > > But as I said, the fact (nr == 0 or 1) would be changed if the > > subpagesize blocksize is supported. > > > > Thanks, > > > > -liubo > > > > > Sincerely, > > > > > > -takafumi > > > > Thanks, > > > > > > > > -liubo > > > > > Sincerely, > > > > > > > > > > On 2017/01/31 5:09, Liu Bo wrote: > > > > > > On Fri, Jan 13, 2017 at 03:12:31PM +0900, takafumi-sslab wrote: > > > > > > > Thanks for your replying. > > > > > > > > > > > > > > I understand this bug is more complicated than I expected. > > > > > > > I classify error cases under submit_extent_page() below > > > > > > > > > > > > > > A: ENOMEM error at btrfs_bio_alloc() in submit_extent_page() > > > > > > > I first assumed this case and sent the mail. > > > > > > > When bio_ret is NULL, submit_extent_page() calls btrfs_bio_alloc(). > > > > > > > Then, btrfs_bio_alloc() may fail and submit_extent_page() returns -ENOMEM. > > > > > > > In this case, bio_endio() is not called and the page's writeback bit > > > > > > > remains. > > > > > > > So, there is a need to call end_page_writeback() in the error handling. > > > > > > > > > > > > > > B: errors under submit_one_bio() of submit_extent_page() > > > > > > > Errors that occur under submit_one_bio() handles at bio_endio(), and > > > > > > > bio_endio() would call end_page_writeback(). > > > > > > > > > > > > > > Therefore, as you mentioned in the last mail, simply adding > > > > > > > end_page_writeback() like my last email and commit 55e3bd2e0c2e1 can > > > > > > > conflict in the case of B. > > > > > > > To avoid such conflict, one easy solution is adding PageWriteback() check > > > > > > > too. > > > > > > > > > > > > > > How do you think of this solution? > > > > > > (sorry for the late reply.) > > > > > > > > > > > > I think its caller, "__extent_writepage", has covered the above case > > > > > > by setting page writeback again. > > > > > > > > > > > > Thanks, > > > > > > > > > > > > -liubo > > > > > > > Sincerely, > > > > > > > > > > > > > > On 2016/12/22 15:20, Liu Bo wrote: > > > > > > > > On Fri, Dec 16, 2016 at 03:41:50PM +0900, Takafumi Kubota wrote: > > > > > > > > > This is actually inspired by Filipe's patch(55e3bd2e0c2e1). > > > > > > > > > > > > > > > > > > When submit_extent_page() in __extent_writepage_io() fails, > > > > > > > > > Btrfs misses clearing a writeback bit of the failed page. > > > > > > > > > This causes the false under-writeback page. > > > > > > > > > Then, another sync task hangs in filemap_fdatawait_range(), > > > > > > > > > because it waits the false under-writeback page. > > > > > > > > > > > > > > > > > > CPU0 CPU1 > > > > > > > > > > > > > > > > > > __extent_writepage_io() > > > > > > > > > ret = submit_extent_page() // fail > > > > > > > > > > > > > > > > > > if (ret) > > > > > > > > > SetPageError(page) > > > > > > > > > // miss clearing the writeback bit > > > > > > > > > > > > > > > > > > sync() > > > > > > > > > ... > > > > > > > > > filemap_fdatawait_range() > > > > > > > > > wait_on_page_writeback(page); > > > > > > > > > // wait the false under-writeback page > > > > > > > > > > > > > > > > > > Signed-off-by: Takafumi Kubota <takafumi.kubota1012@sslab.ics.keio.ac.jp> > > > > > > > > > --- > > > > > > > > > fs/btrfs/extent_io.c | 4 +++- > > > > > > > > > 1 file changed, 3 insertions(+), 1 deletion(-) > > > > > > > > > > > > > > > > > > diff --git a/fs/btrfs/extent_io.c b/fs/btrfs/extent_io.c > > > > > > > > > index 1e67723..ef9793b 100644 > > > > > > > > > --- a/fs/btrfs/extent_io.c > > > > > > > > > +++ b/fs/btrfs/extent_io.c > > > > > > > > > @@ -3443,8 +3443,10 @@ static noinline_for_stack int __extent_writepage_io(struct inode *inode, > > > > > > > > > bdev->bio, max_nr, > > > > > > > > > end_bio_extent_writepage, > > > > > > > > > 0, 0, 0, false); > > > > > > > > > - if (ret) > > > > > > > > > + if (ret) { > > > > > > > > > SetPageError(page); > > > > > > > > > + end_page_writeback(page); > > > > > > > > > + } > > > > > > > > OK...this could be complex as we don't know which part in > > > > > > > > submit_extent_page gets the error, if the page has been added into bio > > > > > > > > and bio_end would call end_page_writepage(page) as well, so whichever > > > > > > > > comes later, the BUG() in end_page_writeback() would complain. > > > > > > > > > > > > > > > > Looks like commit 55e3bd2e0c2e1 also has the same problem although I > > > > > > > > gave it my reviewed-by. > > > > > > > > > > > > > > > > Thanks, > > > > > > > > > > > > > > > > -liubo > > > > > > > > > > > > > > > > > cur = cur + iosize; > > > > > > > > > pg_offset += iosize; > > > > > > > > > -- > > > > > > > > > 1.9.3 > > > > > > > > > > > > > > > > > > -- > > > > > > > > > To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in > > > > > > > > > the body of a message to majordomo@vger.kernel.org > > > > > > > > > More majordomo info at http://vger.kernel.org/majordomo-info.html > > > > > > > -- > > > > > > > Keio University > > > > > > > System Software Laboratory > > > > > > > Takafumi Kubota > > > > > > > takafumi.kubota1012@sslab.ics.keio.jp > > > > > > > > > > > > -- > > > > > Keio University > > > > > System Software Laboratory > > > > > Takafumi Kubota > > > > > takafumi.kubota1012@sslab.ics.keio.jp > > > > > > > > -- > > > Keio University > > > System Software Laboratory > > > Takafumi Kubota > > > takafumi.kubota1012@sslab.ics.keio.jp > > > > > -- > Keio University > System Software Laboratory > Takafumi Kubota > takafumi.kubota1012@sslab.ics.keio.jp > -- To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
On Mon, Feb 06, 2017 at 08:26:54AM -0800, Liu Bo wrote: > On Mon, Feb 06, 2017 at 02:50:18PM +0900, takafumi-sslab wrote: > > > > > > On 2017/02/06 12:35, Liu Bo wrote: > > > a) __extent_writepage has handled the case when nr == 0. > > > > Yes, I agree this. > > > > > b) when nr == 1, the page is marked with writeback bit and added into a > > > bio, thus we have bio_end to deal with page bits. > > > > However, I don't think this is always correct, > > because, as I said before as the Error A, when (bio_ret == NULL or *bio_ret > > == NULL) and btrfs_bio_alloc() fails, the page is not added into a bio. > > Thus, bio_end does not deal with the page's bit, and the writeback bit > > remains with nr == 1. > > > > To confirm this, I inject a fault to mimic the fail of btrfs_bio_alloc(). > > I can reproduce the hang at the kernel ver4.10-rc7 that commit id is > > d5adbfcd5f7bcc6fa58a41c5c5ada0e5c826ce2c > > and Ftrace log messages are like below > > > > a.out-2867 : __extent_writepage: call __extent_writepage_io: > > page:0xffffea000006d200(writeback:0), nr:0, logged at just previous to line > > 3523 of extent_io.c > > a.out-2867 : __extent_writepage_io: call submit_extent_page: > > page:0xffffea000006d200(writeback:1), nr:0, bio_ret:0xffffc90003bd7d40, > > *bio_ret: (null), logged at just previous to line 3443 of extent_io.c > > a.out-2867 : submit_extent_page.isra.53: Mimic Error A: btrfs_bio_alloc() > > fails and submit_extent_page() return -ENOMEM, logged at just previous to > > line 2807 of extent_io.c > > a.out-2867 : __extent_writepage_io: after call submit_extent_page: > > page:0xffffea000006d200(writeback:1), nr:0, bio_ret:0xffffc90003bd7d40, > > *bio_ret: (null), logged at just next to line 3447 of extent_io.c > > a.out-2867 : __extent_writepage_io: nr == 1: > > page:0xffffea000006d200(writeback:1), nr:1, bio_ret:0xffffc90003de7d40, > > logged at just next to line 3456 of extent_io.c //nr == 1 and the writeback > > bit remains > > a.out-2867 : __extent_writepage: after call __extent_writepage_io: > > page:0xffffea000006d200(writeback:1), nr:1, logged at just next to line 3524 > > of extent_io.c // __extent_writepage does not handle, because nr == 1 > > ... > > sync-2868 : __filemap_fdatawait_range: wait_on_page_writeback: > > page:0xffffea000006d200, logged at just previous to line 404 of mm/filemap.c > > // Then, sync hangs > > Thanks for the efforts to prove it, nice. Obviously I missed that @nr > will even be bumped up by one if ENOMEM, so yes, we need to clear the > writeback bit. > > But shouldn't @nr means nr_submitted_successfully? If a submit fails, > it makes no senses to keep submitting subsequent parts. > > Anyway, for now I think the proposed fix is good to solve the problem, so you > may add One thing to add, we still need to check whether page has writeback bit before end_page_writeback. Thanks, -liubo > > Reviewed-by: Liu Bo <bo.li.liu@oracle.com> > > Thanks, > > -liubo > > > > Sincerely, > > > > -takafumi > > > > > > So I don't think the patch is necessary for now. > > > > > > But as I said, the fact (nr == 0 or 1) would be changed if the > > > subpagesize blocksize is supported. > > > > > > Thanks, > > > > > > -liubo > > > > > > > Sincerely, > > > > > > > > -takafumi > > > > > Thanks, > > > > > > > > > > -liubo > > > > > > Sincerely, > > > > > > > > > > > > On 2017/01/31 5:09, Liu Bo wrote: > > > > > > > On Fri, Jan 13, 2017 at 03:12:31PM +0900, takafumi-sslab wrote: > > > > > > > > Thanks for your replying. > > > > > > > > > > > > > > > > I understand this bug is more complicated than I expected. > > > > > > > > I classify error cases under submit_extent_page() below > > > > > > > > > > > > > > > > A: ENOMEM error at btrfs_bio_alloc() in submit_extent_page() > > > > > > > > I first assumed this case and sent the mail. > > > > > > > > When bio_ret is NULL, submit_extent_page() calls btrfs_bio_alloc(). > > > > > > > > Then, btrfs_bio_alloc() may fail and submit_extent_page() returns -ENOMEM. > > > > > > > > In this case, bio_endio() is not called and the page's writeback bit > > > > > > > > remains. > > > > > > > > So, there is a need to call end_page_writeback() in the error handling. > > > > > > > > > > > > > > > > B: errors under submit_one_bio() of submit_extent_page() > > > > > > > > Errors that occur under submit_one_bio() handles at bio_endio(), and > > > > > > > > bio_endio() would call end_page_writeback(). > > > > > > > > > > > > > > > > Therefore, as you mentioned in the last mail, simply adding > > > > > > > > end_page_writeback() like my last email and commit 55e3bd2e0c2e1 can > > > > > > > > conflict in the case of B. > > > > > > > > To avoid such conflict, one easy solution is adding PageWriteback() check > > > > > > > > too. > > > > > > > > > > > > > > > > How do you think of this solution? > > > > > > > (sorry for the late reply.) > > > > > > > > > > > > > > I think its caller, "__extent_writepage", has covered the above case > > > > > > > by setting page writeback again. > > > > > > > > > > > > > > Thanks, > > > > > > > > > > > > > > -liubo > > > > > > > > Sincerely, > > > > > > > > > > > > > > > > On 2016/12/22 15:20, Liu Bo wrote: > > > > > > > > > On Fri, Dec 16, 2016 at 03:41:50PM +0900, Takafumi Kubota wrote: > > > > > > > > > > This is actually inspired by Filipe's patch(55e3bd2e0c2e1). > > > > > > > > > > > > > > > > > > > > When submit_extent_page() in __extent_writepage_io() fails, > > > > > > > > > > Btrfs misses clearing a writeback bit of the failed page. > > > > > > > > > > This causes the false under-writeback page. > > > > > > > > > > Then, another sync task hangs in filemap_fdatawait_range(), > > > > > > > > > > because it waits the false under-writeback page. > > > > > > > > > > > > > > > > > > > > CPU0 CPU1 > > > > > > > > > > > > > > > > > > > > __extent_writepage_io() > > > > > > > > > > ret = submit_extent_page() // fail > > > > > > > > > > > > > > > > > > > > if (ret) > > > > > > > > > > SetPageError(page) > > > > > > > > > > // miss clearing the writeback bit > > > > > > > > > > > > > > > > > > > > sync() > > > > > > > > > > ... > > > > > > > > > > filemap_fdatawait_range() > > > > > > > > > > wait_on_page_writeback(page); > > > > > > > > > > // wait the false under-writeback page > > > > > > > > > > > > > > > > > > > > Signed-off-by: Takafumi Kubota <takafumi.kubota1012@sslab.ics.keio.ac.jp> > > > > > > > > > > --- > > > > > > > > > > fs/btrfs/extent_io.c | 4 +++- > > > > > > > > > > 1 file changed, 3 insertions(+), 1 deletion(-) > > > > > > > > > > > > > > > > > > > > diff --git a/fs/btrfs/extent_io.c b/fs/btrfs/extent_io.c > > > > > > > > > > index 1e67723..ef9793b 100644 > > > > > > > > > > --- a/fs/btrfs/extent_io.c > > > > > > > > > > +++ b/fs/btrfs/extent_io.c > > > > > > > > > > @@ -3443,8 +3443,10 @@ static noinline_for_stack int __extent_writepage_io(struct inode *inode, > > > > > > > > > > bdev->bio, max_nr, > > > > > > > > > > end_bio_extent_writepage, > > > > > > > > > > 0, 0, 0, false); > > > > > > > > > > - if (ret) > > > > > > > > > > + if (ret) { > > > > > > > > > > SetPageError(page); > > > > > > > > > > + end_page_writeback(page); > > > > > > > > > > + } > > > > > > > > > OK...this could be complex as we don't know which part in > > > > > > > > > submit_extent_page gets the error, if the page has been added into bio > > > > > > > > > and bio_end would call end_page_writepage(page) as well, so whichever > > > > > > > > > comes later, the BUG() in end_page_writeback() would complain. > > > > > > > > > > > > > > > > > > Looks like commit 55e3bd2e0c2e1 also has the same problem although I > > > > > > > > > gave it my reviewed-by. > > > > > > > > > > > > > > > > > > Thanks, > > > > > > > > > > > > > > > > > > -liubo > > > > > > > > > > > > > > > > > > > cur = cur + iosize; > > > > > > > > > > pg_offset += iosize; > > > > > > > > > > -- > > > > > > > > > > 1.9.3 > > > > > > > > > > > > > > > > > > > > -- > > > > > > > > > > To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in > > > > > > > > > > the body of a message to majordomo@vger.kernel.org > > > > > > > > > > More majordomo info at http://vger.kernel.org/majordomo-info.html > > > > > > > > -- > > > > > > > > Keio University > > > > > > > > System Software Laboratory > > > > > > > > Takafumi Kubota > > > > > > > > takafumi.kubota1012@sslab.ics.keio.jp > > > > > > > > > > > > > > -- > > > > > > Keio University > > > > > > System Software Laboratory > > > > > > Takafumi Kubota > > > > > > takafumi.kubota1012@sslab.ics.keio.jp > > > > > > > > > > -- > > > > Keio University > > > > System Software Laboratory > > > > Takafumi Kubota > > > > takafumi.kubota1012@sslab.ics.keio.jp > > > > > > > > -- > > Keio University > > System Software Laboratory > > Takafumi Kubota > > takafumi.kubota1012@sslab.ics.keio.jp > > > -- > To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in > the body of a message to majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html -- To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
diff --git a/fs/btrfs/extent_io.c b/fs/btrfs/extent_io.c index 1e67723..ef9793b 100644 --- a/fs/btrfs/extent_io.c +++ b/fs/btrfs/extent_io.c @@ -3443,8 +3443,10 @@ static noinline_for_stack int __extent_writepage_io(struct inode *inode, bdev, &epd->bio, max_nr, end_bio_extent_writepage, 0, 0, 0, false); - if (ret) + if (ret) { SetPageError(page); + end_page_writeback(page); + } cur = cur + iosize; pg_offset += iosize;
This is actually inspired by Filipe's patch(55e3bd2e0c2e1). When submit_extent_page() in __extent_writepage_io() fails, Btrfs misses clearing a writeback bit of the failed page. This causes the false under-writeback page. Then, another sync task hangs in filemap_fdatawait_range(), because it waits the false under-writeback page. CPU0 CPU1 __extent_writepage_io() ret = submit_extent_page() // fail if (ret) SetPageError(page) // miss clearing the writeback bit sync() ... filemap_fdatawait_range() wait_on_page_writeback(page); // wait the false under-writeback page Signed-off-by: Takafumi Kubota <takafumi.kubota1012@sslab.ics.keio.ac.jp> --- fs/btrfs/extent_io.c | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-)