| Message ID | 1378997931-19954-1-git-send-email-sprabhu@redhat.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
On Thu, 12 Sep 2013 15:58:51 +0100 Sachin Prabhu <sprabhu@redhat.com> wrote: > When reading a single page with cifs_readpage(), we make a call to > fscache_read_or_alloc_page() which once done, asynchronously calls > the completion function cifs_readpage_from_fscache_complete(). This > completion function unlocks the page once it has been populated from > cache. The module then attempts to unlock the page a second time in > cifs_readpage() which leads to warning messages. > > In case of a successful call to fscache_read_or_alloc_page() we should skip > the second unlock_page() since this will be called by the > cifs_readpage_from_fscache_complete() once the page has been populated by > fscache. > > With the modifications to cifs_readpage_worker(), we will need to re-grab the > page lock in cifs_write_begin(). > > Signed-off-by: Sachin Prabhu <sprabhu@redhat.com> > --- > fs/cifs/file.c | 10 +++++++--- > 1 file changed, 7 insertions(+), 3 deletions(-) > > diff --git a/fs/cifs/file.c b/fs/cifs/file.c > index 69e8431..98e5222 100644 > --- a/fs/cifs/file.c > +++ b/fs/cifs/file.c > @@ -3423,6 +3423,7 @@ static int cifs_readpage_worker(struct file *file, struct page *page, > io_error: > kunmap(page); > page_cache_release(page); > + unlock_page(page); > > read_complete: > return rc; > @@ -3447,8 +3448,6 @@ static int cifs_readpage(struct file *file, struct page *page) > > rc = cifs_readpage_worker(file, page, &offset); > > - unlock_page(page); > - > free_xid(xid); > return rc; > } > @@ -3502,6 +3501,7 @@ static int cifs_write_begin(struct file *file, struct address_space *mapping, > loff_t pos, unsigned len, unsigned flags, > struct page **pagep, void **fsdata) > { > + int oncethru = 0; > pgoff_t index = pos >> PAGE_CACHE_SHIFT; > loff_t offset = pos & (PAGE_CACHE_SIZE - 1); > loff_t page_start = pos & PAGE_MASK; > @@ -3511,6 +3511,7 @@ static int cifs_write_begin(struct file *file, struct address_space *mapping, > > cifs_dbg(FYI, "write_begin from %lld len %d\n", (long long)pos, len); > > +start: > page = grab_cache_page_write_begin(mapping, index, flags); > if (!page) { > rc = -ENOMEM; > @@ -3552,13 +3553,16 @@ static int cifs_write_begin(struct file *file, struct address_space *mapping, > } > } > > - if ((file->f_flags & O_ACCMODE) != O_WRONLY) { > + if ((file->f_flags & O_ACCMODE) != O_WRONLY && !oncethru) { > /* > * might as well read a page, it is fast enough. If we get > * an error, we don't need to return it. cifs_write_end will > * do a sync write instead since PG_uptodate isn't set. > */ > cifs_readpage_worker(file, page, &page_start); > + page_cache_release(page); > + oncethru = 1; > + goto start; > } else { > /* we could try using another file handle if there is one - > but how would we lock it to prevent close of that handle Looks correct. Nice catch! Reviewed-by: Jeff Layton <jlayton@redhat.com> -- To unsubscribe from this list: send the line "unsubscribe linux-cifs" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
On Thu, 12 Sep 2013 11:35:27 -0400 Jeff Layton <jlayton@redhat.com> wrote: > On Thu, 12 Sep 2013 15:58:51 +0100 > Sachin Prabhu <sprabhu@redhat.com> wrote: > > > When reading a single page with cifs_readpage(), we make a call to > > fscache_read_or_alloc_page() which once done, asynchronously calls > > the completion function cifs_readpage_from_fscache_complete(). This > > completion function unlocks the page once it has been populated from > > cache. The module then attempts to unlock the page a second time in > > cifs_readpage() which leads to warning messages. > > > > In case of a successful call to fscache_read_or_alloc_page() we should skip > > the second unlock_page() since this will be called by the > > cifs_readpage_from_fscache_complete() once the page has been populated by > > fscache. > > > > With the modifications to cifs_readpage_worker(), we will need to re-grab the > > page lock in cifs_write_begin(). > > > > Signed-off-by: Sachin Prabhu <sprabhu@redhat.com> > > --- > > fs/cifs/file.c | 10 +++++++--- > > 1 file changed, 7 insertions(+), 3 deletions(-) > > > > diff --git a/fs/cifs/file.c b/fs/cifs/file.c > > index 69e8431..98e5222 100644 > > --- a/fs/cifs/file.c > > +++ b/fs/cifs/file.c > > @@ -3423,6 +3423,7 @@ static int cifs_readpage_worker(struct file *file, struct page *page, > > io_error: > > kunmap(page); > > page_cache_release(page); > > + unlock_page(page); > > Actually...one preexisting bug that you should probably fix while you're in there. It's a bad idea to unlock the page *after* you release the reference to it. You probably want to move that unlock_page call before the page_cache_release. OTOH...it's not clear to me why we're bumping the refcount on the page at all in cifs_readpage_worker. Clearly we must have a reference to it already or it won't be ok to just pass in the pointer to it. Maybe it'd be better to just make it clear that cifs_readpage_worker must be called with the page pinned and get rid of the extra refcounting in that function altogether. Sound reasonable? > > read_complete: > > return rc; > > @@ -3447,8 +3448,6 @@ static int cifs_readpage(struct file *file, struct page *page) > > > > rc = cifs_readpage_worker(file, page, &offset); > > > > - unlock_page(page); > > - > > free_xid(xid); > > return rc; > > } > > @@ -3502,6 +3501,7 @@ static int cifs_write_begin(struct file *file, struct address_space *mapping, > > loff_t pos, unsigned len, unsigned flags, > > struct page **pagep, void **fsdata) > > { > > + int oncethru = 0; > > pgoff_t index = pos >> PAGE_CACHE_SHIFT; > > loff_t offset = pos & (PAGE_CACHE_SIZE - 1); > > loff_t page_start = pos & PAGE_MASK; > > @@ -3511,6 +3511,7 @@ static int cifs_write_begin(struct file *file, struct address_space *mapping, > > > > cifs_dbg(FYI, "write_begin from %lld len %d\n", (long long)pos, len); > > > > +start: > > page = grab_cache_page_write_begin(mapping, index, flags); > > if (!page) { > > rc = -ENOMEM; > > @@ -3552,13 +3553,16 @@ static int cifs_write_begin(struct file *file, struct address_space *mapping, > > } > > } > > > > - if ((file->f_flags & O_ACCMODE) != O_WRONLY) { > > + if ((file->f_flags & O_ACCMODE) != O_WRONLY && !oncethru) { > > /* > > * might as well read a page, it is fast enough. If we get > > * an error, we don't need to return it. cifs_write_end will > > * do a sync write instead since PG_uptodate isn't set. > > */ > > cifs_readpage_worker(file, page, &page_start); > > + page_cache_release(page); > > + oncethru = 1; > > + goto start; > > } else { > > /* we could try using another file handle if there is one - > > but how would we lock it to prevent close of that handle > > Looks correct. Nice catch! > > Reviewed-by: Jeff Layton <jlayton@redhat.com> > -- > To unsubscribe from this list: send the line "unsubscribe linux-cifs" in > the body of a message to majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html
Also would be helpful to have the link to any external bug report (if any) On Thu, Sep 12, 2013 at 10:42 AM, Jeff Layton <jlayton@poochiereds.net> wrote: > On Thu, 12 Sep 2013 11:35:27 -0400 > Jeff Layton <jlayton@redhat.com> wrote: > >> On Thu, 12 Sep 2013 15:58:51 +0100 >> Sachin Prabhu <sprabhu@redhat.com> wrote: >> >> > When reading a single page with cifs_readpage(), we make a call to >> > fscache_read_or_alloc_page() which once done, asynchronously calls >> > the completion function cifs_readpage_from_fscache_complete(). This >> > completion function unlocks the page once it has been populated from >> > cache. The module then attempts to unlock the page a second time in >> > cifs_readpage() which leads to warning messages. >> > >> > In case of a successful call to fscache_read_or_alloc_page() we should skip >> > the second unlock_page() since this will be called by the >> > cifs_readpage_from_fscache_complete() once the page has been populated by >> > fscache. >> > >> > With the modifications to cifs_readpage_worker(), we will need to re-grab the >> > page lock in cifs_write_begin(). >> > >> > Signed-off-by: Sachin Prabhu <sprabhu@redhat.com> >> > --- >> > fs/cifs/file.c | 10 +++++++--- >> > 1 file changed, 7 insertions(+), 3 deletions(-) >> > >> > diff --git a/fs/cifs/file.c b/fs/cifs/file.c >> > index 69e8431..98e5222 100644 >> > --- a/fs/cifs/file.c >> > +++ b/fs/cifs/file.c >> > @@ -3423,6 +3423,7 @@ static int cifs_readpage_worker(struct file *file, struct page *page, >> > io_error: >> > kunmap(page); >> > page_cache_release(page); >> > + unlock_page(page); >> > > > Actually...one preexisting bug that you should probably fix while > you're in there. It's a bad idea to unlock the page *after* you release > the reference to it. You probably want to move that unlock_page call > before the page_cache_release. > > OTOH...it's not clear to me why we're bumping the refcount on the > page at all in cifs_readpage_worker. Clearly we must have a reference > to it already or it won't be ok to just pass in the pointer to it. > Maybe it'd be better to just make it clear that cifs_readpage_worker > must be called with the page pinned and get rid of the extra > refcounting in that function altogether. > > Sound reasonable? > >> > read_complete: >> > return rc; >> > @@ -3447,8 +3448,6 @@ static int cifs_readpage(struct file *file, struct page *page) >> > >> > rc = cifs_readpage_worker(file, page, &offset); >> > >> > - unlock_page(page); >> > - >> > free_xid(xid); >> > return rc; >> > } >> > @@ -3502,6 +3501,7 @@ static int cifs_write_begin(struct file *file, struct address_space *mapping, >> > loff_t pos, unsigned len, unsigned flags, >> > struct page **pagep, void **fsdata) >> > { >> > + int oncethru = 0; >> > pgoff_t index = pos >> PAGE_CACHE_SHIFT; >> > loff_t offset = pos & (PAGE_CACHE_SIZE - 1); >> > loff_t page_start = pos & PAGE_MASK; >> > @@ -3511,6 +3511,7 @@ static int cifs_write_begin(struct file *file, struct address_space *mapping, >> > >> > cifs_dbg(FYI, "write_begin from %lld len %d\n", (long long)pos, len); >> > >> > +start: >> > page = grab_cache_page_write_begin(mapping, index, flags); >> > if (!page) { >> > rc = -ENOMEM; >> > @@ -3552,13 +3553,16 @@ static int cifs_write_begin(struct file *file, struct address_space *mapping, >> > } >> > } >> > >> > - if ((file->f_flags & O_ACCMODE) != O_WRONLY) { >> > + if ((file->f_flags & O_ACCMODE) != O_WRONLY && !oncethru) { >> > /* >> > * might as well read a page, it is fast enough. If we get >> > * an error, we don't need to return it. cifs_write_end will >> > * do a sync write instead since PG_uptodate isn't set. >> > */ >> > cifs_readpage_worker(file, page, &page_start); >> > + page_cache_release(page); >> > + oncethru = 1; >> > + goto start; >> > } else { >> > /* we could try using another file handle if there is one - >> > but how would we lock it to prevent close of that handle >> >> Looks correct. Nice catch! >> >> Reviewed-by: Jeff Layton <jlayton@redhat.com> >> -- >> To unsubscribe from this list: send the line "unsubscribe linux-cifs" in >> the body of a message to majordomo@vger.kernel.org >> More majordomo info at http://vger.kernel.org/majordomo-info.html > > > -- > Jeff Layton <jlayton@poochiereds.net>
Looking at this:
static int cifs_readpage_worker(struct file *file, struct page *page,
loff_t *poffset)
{
char *read_data;
int rc;
/* Is the page cached? */
rc = cifs_readpage_from_fscache(file_inode(file), page);
if (rc == 0)
goto read_complete;
Should you return here if rc == -ENOMEM or -ERESTARTSYS? That might break
cifs_write_begin() though - which perhaps ought to check the return value.
Your patch, however, looks okay otherwise, so feel free to add:
Acked-by: David Howells <dhowells@redhat.com>
David
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On Fri, 2013-09-13 at 14:30 +0100, David Howells wrote: > Looking at this: > > static int cifs_readpage_worker(struct file *file, struct page *page, > loff_t *poffset) > { > char *read_data; > int rc; > > /* Is the page cached? */ > rc = cifs_readpage_from_fscache(file_inode(file), page); > if (rc == 0) > goto read_complete; > > Should you return here if rc == -ENOMEM or -ERESTARTSYS? That might break > cifs_write_begin() though - which perhaps ought to check the return value. > > Your patch, however, looks okay otherwise, so feel free to add: > > Acked-by: David Howells <dhowells@redhat.com> > > David According to the comment already above the call to cifs_readpage_worker() in cifs_write_begin(): /* * might as well read a page, it is fast enough. If we get * an error, we don't need to return it. cifs_write_end will * do a sync write instead since PG_uptodate isn't set. */ With the patch, we ignore the error and set oncethru to 1 so that we don't attempt to call cifs_readpage_worker() again and let cifs_write_end do a sync_write. Sachin Prabhu -- To unsubscribe from this list: send the line "unsubscribe linux-cifs" 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/cifs/file.c b/fs/cifs/file.c index 69e8431..98e5222 100644 --- a/fs/cifs/file.c +++ b/fs/cifs/file.c @@ -3423,6 +3423,7 @@ static int cifs_readpage_worker(struct file *file, struct page *page, io_error: kunmap(page); page_cache_release(page); + unlock_page(page); read_complete: return rc; @@ -3447,8 +3448,6 @@ static int cifs_readpage(struct file *file, struct page *page) rc = cifs_readpage_worker(file, page, &offset); - unlock_page(page); - free_xid(xid); return rc; } @@ -3502,6 +3501,7 @@ static int cifs_write_begin(struct file *file, struct address_space *mapping, loff_t pos, unsigned len, unsigned flags, struct page **pagep, void **fsdata) { + int oncethru = 0; pgoff_t index = pos >> PAGE_CACHE_SHIFT; loff_t offset = pos & (PAGE_CACHE_SIZE - 1); loff_t page_start = pos & PAGE_MASK; @@ -3511,6 +3511,7 @@ static int cifs_write_begin(struct file *file, struct address_space *mapping, cifs_dbg(FYI, "write_begin from %lld len %d\n", (long long)pos, len); +start: page = grab_cache_page_write_begin(mapping, index, flags); if (!page) { rc = -ENOMEM; @@ -3552,13 +3553,16 @@ static int cifs_write_begin(struct file *file, struct address_space *mapping, } } - if ((file->f_flags & O_ACCMODE) != O_WRONLY) { + if ((file->f_flags & O_ACCMODE) != O_WRONLY && !oncethru) { /* * might as well read a page, it is fast enough. If we get * an error, we don't need to return it. cifs_write_end will * do a sync write instead since PG_uptodate isn't set. */ cifs_readpage_worker(file, page, &page_start); + page_cache_release(page); + oncethru = 1; + goto start; } else { /* we could try using another file handle if there is one - but how would we lock it to prevent close of that handle
When reading a single page with cifs_readpage(), we make a call to fscache_read_or_alloc_page() which once done, asynchronously calls the completion function cifs_readpage_from_fscache_complete(). This completion function unlocks the page once it has been populated from cache. The module then attempts to unlock the page a second time in cifs_readpage() which leads to warning messages. In case of a successful call to fscache_read_or_alloc_page() we should skip the second unlock_page() since this will be called by the cifs_readpage_from_fscache_complete() once the page has been populated by fscache. With the modifications to cifs_readpage_worker(), we will need to re-grab the page lock in cifs_write_begin(). Signed-off-by: Sachin Prabhu <sprabhu@redhat.com> --- fs/cifs/file.c | 10 +++++++--- 1 file changed, 7 insertions(+), 3 deletions(-)