| Message ID | 1563816648-12057-1-git-send-email-linux@roeck-us.net (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | bfq: Check if bfqq is NULL in bfq_insert_request | expand |
On Mon, Jul 22, 2019 at 10:30:48AM -0700, Guenter Roeck wrote: > In bfq_insert_request(), bfqq is initialized with: > bfqq = bfq_init_rq(rq); > In bfq_init_rq(), we find: > if (unlikely(!rq->elv.icq)) > return NULL; > Indeed, rq->elv.icq can be NULL if the memory allocation in > create_task_io_context() failed. > The above function should have been ioc_create_icq(), sorry. Guenter > A comment in bfq_insert_request() suggests that bfqq is supposed to be > non-NULL if 'at_head || blk_rq_is_passthrough(rq)' is false. Yet, as > debugging and practical experience shows, this is not the case in the > above situation. > > This results in the following crash. > > Unable to handle kernel NULL pointer dereference > at virtual address 00000000000001b0 > ... > Call trace: > bfq_setup_cooperator+0x44/0x134 > bfq_insert_requests+0x10c/0x630 > blk_mq_sched_insert_requests+0x60/0xb4 > blk_mq_flush_plug_list+0x290/0x2d4 > blk_flush_plug_list+0xe0/0x230 > blk_finish_plug+0x30/0x40 > generic_writepages+0x60/0x94 > blkdev_writepages+0x24/0x30 > do_writepages+0x74/0xac > __filemap_fdatawrite_range+0x94/0xc8 > file_write_and_wait_range+0x44/0xa0 > blkdev_fsync+0x38/0x68 > vfs_fsync_range+0x68/0x80 > do_fsync+0x44/0x80 > > The problem is relatively easy to reproduce by running an image with > failslab enabled, such as with: > > cd /sys/kernel/debug/failslab > echo 10 > probability > echo 300 > times > > Avoid the problem by checking if bfqq is NULL before using it. With the > NULL check in place, requests with missing io context are queued > immediately, and the crash is no longer seen. > > Fixes: 18e5a57d79878 ("block, bfq: postpone rq preparation to insert or merge") > Reported-by: Hsin-Yi Wang <hsinyi@google.com> > Cc: Hsin-Yi Wang <hsinyi@google.com> > Cc: Nicolas Boichat <drinkcat@chromium.org> > Cc: Doug Anderson <dianders@chromium.org> > Signed-off-by: Guenter Roeck <linux@roeck-us.net> > --- > block/bfq-iosched.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/block/bfq-iosched.c b/block/bfq-iosched.c > index 72860325245a..56f3f4227010 100644 > --- a/block/bfq-iosched.c > +++ b/block/bfq-iosched.c > @@ -5417,7 +5417,7 @@ static void bfq_insert_request(struct blk_mq_hw_ctx *hctx, struct request *rq, > > spin_lock_irq(&bfqd->lock); > bfqq = bfq_init_rq(rq); > - if (at_head || blk_rq_is_passthrough(rq)) { > + if (!bfqq || at_head || blk_rq_is_passthrough(rq)) { > if (at_head) > list_add(&rq->queuelist, &bfqd->dispatch); > else > -- > 2.7.4 >
On 7/23/19 4:29 AM, Guenter Roeck wrote: > On Mon, Jul 22, 2019 at 10:30:48AM -0700, Guenter Roeck wrote: >> In bfq_insert_request(), bfqq is initialized with: >> bfqq = bfq_init_rq(rq); >> In bfq_init_rq(), we find: >> if (unlikely(!rq->elv.icq)) >> return NULL; >> Indeed, rq->elv.icq can be NULL if the memory allocation in >> create_task_io_context() failed. >> > > The above function should have been ioc_create_icq(), sorry. > > Guenter > >> A comment in bfq_insert_request() suggests that bfqq is supposed to be >> non-NULL if 'at_head || blk_rq_is_passthrough(rq)' is false. Yet, as >> debugging and practical experience shows, this is not the case in the >> above situation. >> >> This results in the following crash. >> >> Unable to handle kernel NULL pointer dereference >> at virtual address 00000000000001b0 >> ... >> Call trace: >> bfq_setup_cooperator+0x44/0x134 >> bfq_insert_requests+0x10c/0x630 >> blk_mq_sched_insert_requests+0x60/0xb4 >> blk_mq_flush_plug_list+0x290/0x2d4 >> blk_flush_plug_list+0xe0/0x230 >> blk_finish_plug+0x30/0x40 >> generic_writepages+0x60/0x94 >> blkdev_writepages+0x24/0x30 >> do_writepages+0x74/0xac >> __filemap_fdatawrite_range+0x94/0xc8 >> file_write_and_wait_range+0x44/0xa0 >> blkdev_fsync+0x38/0x68 >> vfs_fsync_range+0x68/0x80 >> do_fsync+0x44/0x80 >> >> The problem is relatively easy to reproduce by running an image with >> failslab enabled, such as with: >> >> cd /sys/kernel/debug/failslab >> echo 10 > probability >> echo 300 > times >> >> Avoid the problem by checking if bfqq is NULL before using it. With the >> NULL check in place, requests with missing io context are queued >> immediately, and the crash is no longer seen. >> What about other place use blk_init_rq()? E.g in bfq_request_merged(): 1897 struct bfq_queue *bfqq = bfq_init_rq(req); 1898 struct bfq_data *bfqd = bfqq->bfqd; Which may have same Null-pointer bug? -Bob >> Fixes: 18e5a57d79878 ("block, bfq: postpone rq preparation to insert or merge") >> Reported-by: Hsin-Yi Wang <hsinyi@google.com> >> Cc: Hsin-Yi Wang <hsinyi@google.com> >> Cc: Nicolas Boichat <drinkcat@chromium.org> >> Cc: Doug Anderson <dianders@chromium.org> >> Signed-off-by: Guenter Roeck <linux@roeck-us.net> >> --- >> block/bfq-iosched.c | 2 +- >> 1 file changed, 1 insertion(+), 1 deletion(-) >> >> diff --git a/block/bfq-iosched.c b/block/bfq-iosched.c >> index 72860325245a..56f3f4227010 100644 >> --- a/block/bfq-iosched.c >> +++ b/block/bfq-iosched.c >> @@ -5417,7 +5417,7 @@ static void bfq_insert_request(struct blk_mq_hw_ctx *hctx, struct request *rq, >> >> spin_lock_irq(&bfqd->lock); >> bfqq = bfq_init_rq(rq); >> - if (at_head || blk_rq_is_passthrough(rq)) { >> + if (!bfqq || at_head || blk_rq_is_passthrough(rq)) { >> if (at_head) >> list_add(&rq->queuelist, &bfqd->dispatch); >> else >> -- >> 2.7.4 >>
On Tue, Jul 23, 2019 at 07:36:16AM +0800, Bob Liu wrote: > On 7/23/19 4:29 AM, Guenter Roeck wrote: > > On Mon, Jul 22, 2019 at 10:30:48AM -0700, Guenter Roeck wrote: > >> In bfq_insert_request(), bfqq is initialized with: > >> bfqq = bfq_init_rq(rq); > >> In bfq_init_rq(), we find: > >> if (unlikely(!rq->elv.icq)) > >> return NULL; > >> Indeed, rq->elv.icq can be NULL if the memory allocation in > >> create_task_io_context() failed. > >> > > > > The above function should have been ioc_create_icq(), sorry. > > > > Guenter > > > >> A comment in bfq_insert_request() suggests that bfqq is supposed to be > >> non-NULL if 'at_head || blk_rq_is_passthrough(rq)' is false. Yet, as > >> debugging and practical experience shows, this is not the case in the > >> above situation. > >> > >> This results in the following crash. > >> > >> Unable to handle kernel NULL pointer dereference > >> at virtual address 00000000000001b0 > >> ... > >> Call trace: > >> bfq_setup_cooperator+0x44/0x134 > >> bfq_insert_requests+0x10c/0x630 > >> blk_mq_sched_insert_requests+0x60/0xb4 > >> blk_mq_flush_plug_list+0x290/0x2d4 > >> blk_flush_plug_list+0xe0/0x230 > >> blk_finish_plug+0x30/0x40 > >> generic_writepages+0x60/0x94 > >> blkdev_writepages+0x24/0x30 > >> do_writepages+0x74/0xac > >> __filemap_fdatawrite_range+0x94/0xc8 > >> file_write_and_wait_range+0x44/0xa0 > >> blkdev_fsync+0x38/0x68 > >> vfs_fsync_range+0x68/0x80 > >> do_fsync+0x44/0x80 > >> > >> The problem is relatively easy to reproduce by running an image with > >> failslab enabled, such as with: > >> > >> cd /sys/kernel/debug/failslab > >> echo 10 > probability > >> echo 300 > times > >> > >> Avoid the problem by checking if bfqq is NULL before using it. With the > >> NULL check in place, requests with missing io context are queued > >> immediately, and the crash is no longer seen. > >> > > > What about other place use blk_init_rq()? > E.g in bfq_request_merged(): > 1897 struct bfq_queue *bfqq = bfq_init_rq(req); > 1898 struct bfq_data *bfqd = bfqq->bfqd; > > Which may have same Null-pointer bug? > Good question. Doug asked it as well. My understanding is that the code won't hit those places since bfq is essentially bypassed. Of course, I may be completely wrong, so we should wait for Paolo to confirm if I my understanding is correct (or wrong). Thanks, Guenter > -Bob > > >> Fixes: 18e5a57d79878 ("block, bfq: postpone rq preparation to insert or merge") > >> Reported-by: Hsin-Yi Wang <hsinyi@google.com> > >> Cc: Hsin-Yi Wang <hsinyi@google.com> > >> Cc: Nicolas Boichat <drinkcat@chromium.org> > >> Cc: Doug Anderson <dianders@chromium.org> > >> Signed-off-by: Guenter Roeck <linux@roeck-us.net> > >> --- > >> block/bfq-iosched.c | 2 +- > >> 1 file changed, 1 insertion(+), 1 deletion(-) > >> > >> diff --git a/block/bfq-iosched.c b/block/bfq-iosched.c > >> index 72860325245a..56f3f4227010 100644 > >> --- a/block/bfq-iosched.c > >> +++ b/block/bfq-iosched.c > >> @@ -5417,7 +5417,7 @@ static void bfq_insert_request(struct blk_mq_hw_ctx *hctx, struct request *rq, > >> > >> spin_lock_irq(&bfqd->lock); > >> bfqq = bfq_init_rq(rq); > >> - if (at_head || blk_rq_is_passthrough(rq)) { > >> + if (!bfqq || at_head || blk_rq_is_passthrough(rq)) { > >> if (at_head) > >> list_add(&rq->queuelist, &bfqd->dispatch); > >> else > >> -- > >> 2.7.4 > >> >
ping ... just in case this patch got lost in Paolo's queue. Guenter On Mon, Jul 22, 2019 at 10:30:48AM -0700, Guenter Roeck wrote: > In bfq_insert_request(), bfqq is initialized with: > bfqq = bfq_init_rq(rq); > In bfq_init_rq(), we find: > if (unlikely(!rq->elv.icq)) > return NULL; > Indeed, rq->elv.icq can be NULL if the memory allocation in > create_task_io_context() failed. > > A comment in bfq_insert_request() suggests that bfqq is supposed to be > non-NULL if 'at_head || blk_rq_is_passthrough(rq)' is false. Yet, as > debugging and practical experience shows, this is not the case in the > above situation. > > This results in the following crash. > > Unable to handle kernel NULL pointer dereference > at virtual address 00000000000001b0 > ... > Call trace: > bfq_setup_cooperator+0x44/0x134 > bfq_insert_requests+0x10c/0x630 > blk_mq_sched_insert_requests+0x60/0xb4 > blk_mq_flush_plug_list+0x290/0x2d4 > blk_flush_plug_list+0xe0/0x230 > blk_finish_plug+0x30/0x40 > generic_writepages+0x60/0x94 > blkdev_writepages+0x24/0x30 > do_writepages+0x74/0xac > __filemap_fdatawrite_range+0x94/0xc8 > file_write_and_wait_range+0x44/0xa0 > blkdev_fsync+0x38/0x68 > vfs_fsync_range+0x68/0x80 > do_fsync+0x44/0x80 > > The problem is relatively easy to reproduce by running an image with > failslab enabled, such as with: > > cd /sys/kernel/debug/failslab > echo 10 > probability > echo 300 > times > > Avoid the problem by checking if bfqq is NULL before using it. With the > NULL check in place, requests with missing io context are queued > immediately, and the crash is no longer seen. > > Fixes: 18e5a57d79878 ("block, bfq: postpone rq preparation to insert or merge") > Reported-by: Hsin-Yi Wang <hsinyi@google.com> > Cc: Hsin-Yi Wang <hsinyi@google.com> > Cc: Nicolas Boichat <drinkcat@chromium.org> > Cc: Doug Anderson <dianders@chromium.org> > Signed-off-by: Guenter Roeck <linux@roeck-us.net> > --- > block/bfq-iosched.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/block/bfq-iosched.c b/block/bfq-iosched.c > index 72860325245a..56f3f4227010 100644 > --- a/block/bfq-iosched.c > +++ b/block/bfq-iosched.c > @@ -5417,7 +5417,7 @@ static void bfq_insert_request(struct blk_mq_hw_ctx *hctx, struct request *rq, > > spin_lock_irq(&bfqd->lock); > bfqq = bfq_init_rq(rq); > - if (at_head || blk_rq_is_passthrough(rq)) { > + if (!bfqq || at_head || blk_rq_is_passthrough(rq)) { > if (at_head) > list_add(&rq->queuelist, &bfqd->dispatch); > else > -- > 2.7.4 >
Hi Guenter, sorry for the delay (Dolomiti's fault). I didn't consider that rq->elv-icq might have been NULL also because of OOM. Thanks for spotting this issue. As for the other places where the return value of bfq_init_rq is used, unfortunately I think they matter too. Those other places are related to request merging, which is the alternative destiny of requests (instead of being just inserted). But, regardless of whether a request is to be merged or inserted, that request may be destined to a bfq_queue (possibly merged with a request already in a bfq_queue), and a NULL return value by bfq_init_rq leads to a crash. I guess you can reproduce your failure also for the merge case, by generating sequential, direct I/O with queue depth > 1, and of course by enabling failslab. If my considerations above are correct, do you want to propose a complete fix yourself? Thanks, Paolo > Il giorno 28 lug 2019, alle ore 17:19, Guenter Roeck <linux@roeck-us.net> ha scritto: > > ping ... just in case this patch got lost in Paolo's queue. > > Guenter > > On Mon, Jul 22, 2019 at 10:30:48AM -0700, Guenter Roeck wrote: >> In bfq_insert_request(), bfqq is initialized with: >> bfqq = bfq_init_rq(rq); >> In bfq_init_rq(), we find: >> if (unlikely(!rq->elv.icq)) >> return NULL; >> Indeed, rq->elv.icq can be NULL if the memory allocation in >> create_task_io_context() failed. >> >> A comment in bfq_insert_request() suggests that bfqq is supposed to be >> non-NULL if 'at_head || blk_rq_is_passthrough(rq)' is false. Yet, as >> debugging and practical experience shows, this is not the case in the >> above situation. >> >> This results in the following crash. >> >> Unable to handle kernel NULL pointer dereference >> at virtual address 00000000000001b0 >> ... >> Call trace: >> bfq_setup_cooperator+0x44/0x134 >> bfq_insert_requests+0x10c/0x630 >> blk_mq_sched_insert_requests+0x60/0xb4 >> blk_mq_flush_plug_list+0x290/0x2d4 >> blk_flush_plug_list+0xe0/0x230 >> blk_finish_plug+0x30/0x40 >> generic_writepages+0x60/0x94 >> blkdev_writepages+0x24/0x30 >> do_writepages+0x74/0xac >> __filemap_fdatawrite_range+0x94/0xc8 >> file_write_and_wait_range+0x44/0xa0 >> blkdev_fsync+0x38/0x68 >> vfs_fsync_range+0x68/0x80 >> do_fsync+0x44/0x80 >> >> The problem is relatively easy to reproduce by running an image with >> failslab enabled, such as with: >> >> cd /sys/kernel/debug/failslab >> echo 10 > probability >> echo 300 > times >> >> Avoid the problem by checking if bfqq is NULL before using it. With the >> NULL check in place, requests with missing io context are queued >> immediately, and the crash is no longer seen. >> >> Fixes: 18e5a57d79878 ("block, bfq: postpone rq preparation to insert or merge") >> Reported-by: Hsin-Yi Wang <hsinyi@google.com> >> Cc: Hsin-Yi Wang <hsinyi@google.com> >> Cc: Nicolas Boichat <drinkcat@chromium.org> >> Cc: Doug Anderson <dianders@chromium.org> >> Signed-off-by: Guenter Roeck <linux@roeck-us.net> >> --- >> block/bfq-iosched.c | 2 +- >> 1 file changed, 1 insertion(+), 1 deletion(-) >> >> diff --git a/block/bfq-iosched.c b/block/bfq-iosched.c >> index 72860325245a..56f3f4227010 100644 >> --- a/block/bfq-iosched.c >> +++ b/block/bfq-iosched.c >> @@ -5417,7 +5417,7 @@ static void bfq_insert_request(struct blk_mq_hw_ctx *hctx, struct request *rq, >> >> spin_lock_irq(&bfqd->lock); >> bfqq = bfq_init_rq(rq); >> - if (at_head || blk_rq_is_passthrough(rq)) { >> + if (!bfqq || at_head || blk_rq_is_passthrough(rq)) { >> if (at_head) >> list_add(&rq->queuelist, &bfqd->dispatch); >> else >> -- >> 2.7.4 >>
On 7/30/19 1:55 AM, Paolo Valente wrote: > Hi Guenter, > sorry for the delay (Dolomiti's fault). > > I didn't consider that rq->elv-icq might have been NULL also > because of OOM. Thanks for spotting this issue. > > As for the other places where the return value of bfq_init_rq is used, > unfortunately I think they matter too. Those other places are related > to request merging, which is the alternative destiny of requests > (instead of being just inserted). But, regardless of whether a > request is to be merged or inserted, that request may be destined to a > bfq_queue (possibly merged with a request already in a bfq_queue), and > a NULL return value by bfq_init_rq leads to a crash. I guess you can > reproduce your failure also for the merge case, by generating > sequential, direct I/O with queue depth > 1, and of course by enabling > failslab. > My assumption was that requests would only be merged if they are associated with the same io context. In that case, that IO context isn't reallocated with ioc_create_icq() but reused, and icq would thus never be NULL. I guess that assumption was wrong. > If my considerations above are correct, do you want to propose a > complete fix yourself? > Sure, I'll send an updated patch. Thanks, Guenter > Thanks, > Paolo > >> Il giorno 28 lug 2019, alle ore 17:19, Guenter Roeck <linux@roeck-us.net> ha scritto: >> >> ping ... just in case this patch got lost in Paolo's queue. >> >> Guenter >> >> On Mon, Jul 22, 2019 at 10:30:48AM -0700, Guenter Roeck wrote: >>> In bfq_insert_request(), bfqq is initialized with: >>> bfqq = bfq_init_rq(rq); >>> In bfq_init_rq(), we find: >>> if (unlikely(!rq->elv.icq)) >>> return NULL; >>> Indeed, rq->elv.icq can be NULL if the memory allocation in >>> create_task_io_context() failed. >>> >>> A comment in bfq_insert_request() suggests that bfqq is supposed to be >>> non-NULL if 'at_head || blk_rq_is_passthrough(rq)' is false. Yet, as >>> debugging and practical experience shows, this is not the case in the >>> above situation. >>> >>> This results in the following crash. >>> >>> Unable to handle kernel NULL pointer dereference >>> at virtual address 00000000000001b0 >>> ... >>> Call trace: >>> bfq_setup_cooperator+0x44/0x134 >>> bfq_insert_requests+0x10c/0x630 >>> blk_mq_sched_insert_requests+0x60/0xb4 >>> blk_mq_flush_plug_list+0x290/0x2d4 >>> blk_flush_plug_list+0xe0/0x230 >>> blk_finish_plug+0x30/0x40 >>> generic_writepages+0x60/0x94 >>> blkdev_writepages+0x24/0x30 >>> do_writepages+0x74/0xac >>> __filemap_fdatawrite_range+0x94/0xc8 >>> file_write_and_wait_range+0x44/0xa0 >>> blkdev_fsync+0x38/0x68 >>> vfs_fsync_range+0x68/0x80 >>> do_fsync+0x44/0x80 >>> >>> The problem is relatively easy to reproduce by running an image with >>> failslab enabled, such as with: >>> >>> cd /sys/kernel/debug/failslab >>> echo 10 > probability >>> echo 300 > times >>> >>> Avoid the problem by checking if bfqq is NULL before using it. With the >>> NULL check in place, requests with missing io context are queued >>> immediately, and the crash is no longer seen. >>> >>> Fixes: 18e5a57d79878 ("block, bfq: postpone rq preparation to insert or merge") >>> Reported-by: Hsin-Yi Wang <hsinyi@google.com> >>> Cc: Hsin-Yi Wang <hsinyi@google.com> >>> Cc: Nicolas Boichat <drinkcat@chromium.org> >>> Cc: Doug Anderson <dianders@chromium.org> >>> Signed-off-by: Guenter Roeck <linux@roeck-us.net> >>> --- >>> block/bfq-iosched.c | 2 +- >>> 1 file changed, 1 insertion(+), 1 deletion(-) >>> >>> diff --git a/block/bfq-iosched.c b/block/bfq-iosched.c >>> index 72860325245a..56f3f4227010 100644 >>> --- a/block/bfq-iosched.c >>> +++ b/block/bfq-iosched.c >>> @@ -5417,7 +5417,7 @@ static void bfq_insert_request(struct blk_mq_hw_ctx *hctx, struct request *rq, >>> >>> spin_lock_irq(&bfqd->lock); >>> bfqq = bfq_init_rq(rq); >>> - if (at_head || blk_rq_is_passthrough(rq)) { >>> + if (!bfqq || at_head || blk_rq_is_passthrough(rq)) { >>> if (at_head) >>> list_add(&rq->queuelist, &bfqd->dispatch); >>> else >>> -- >>> 2.7.4 >>> > >
Paolo, On Tue, Jul 30, 2019 at 10:55:24AM +0200, Paolo Valente wrote: > Hi Guenter, > sorry for the delay (Dolomiti's fault). > > I didn't consider that rq->elv-icq might have been NULL also > because of OOM. Thanks for spotting this issue. > > As for the other places where the return value of bfq_init_rq is used, > unfortunately I think they matter too. Those other places are related > to request merging, which is the alternative destiny of requests > (instead of being just inserted). But, regardless of whether a > request is to be merged or inserted, that request may be destined to a > bfq_queue (possibly merged with a request already in a bfq_queue), and > a NULL return value by bfq_init_rq leads to a crash. I guess you can > reproduce your failure also for the merge case, by generating > sequential, direct I/O with queue depth > 1, and of course by enabling > failslab. > > If my considerations above are correct, do you want to propose a > complete fix yourself? > I had another look into the code. Unfortunately, both bfq_request_merged() and bfq_requests_merged() simply assume that bfq_init_rq() never returns NULL, and don't give me an idea for a path of action if it returns NULL after all. I'll have to pass the problem off to you for a fix. Thanks, Guenter
> Il giorno 30 lug 2019, alle ore 15:35, Guenter Roeck <linux@roeck-us.net> ha scritto: > > On 7/30/19 1:55 AM, Paolo Valente wrote: >> Hi Guenter, >> sorry for the delay (Dolomiti's fault). >> I didn't consider that rq->elv-icq might have been NULL also >> because of OOM. Thanks for spotting this issue. >> As for the other places where the return value of bfq_init_rq is used, >> unfortunately I think they matter too. Those other places are related >> to request merging, which is the alternative destiny of requests >> (instead of being just inserted). But, regardless of whether a >> request is to be merged or inserted, that request may be destined to a >> bfq_queue (possibly merged with a request already in a bfq_queue), and >> a NULL return value by bfq_init_rq leads to a crash. I guess you can >> reproduce your failure also for the merge case, by generating >> sequential, direct I/O with queue depth > 1, and of course by enabling >> failslab. > My assumption was that requests would only be merged if they are associated > with the same io context. In that case, that IO context isn't reallocated > with ioc_create_icq() but reused, and icq would thus never be NULL. > I guess that assumption was wrong. I don't remember such a filtering. I had a look again, but didn't find anything relevant. However, more competent people see these emails. Maybe someone can give us better advice. Otherwise, to stay on the safe side, I'd propose to handle any possible NULL return. And I'll manage it, as per your request. Thanks, Paolo > >> If my considerations above are correct, do you want to propose a >> complete fix yourself? > > Sure, I'll send an updated patch. > > Thanks, > Guenter > >> Thanks, >> Paolo >>> Il giorno 28 lug 2019, alle ore 17:19, Guenter Roeck <linux@roeck-us.net> ha scritto: >>> >>> ping ... just in case this patch got lost in Paolo's queue. >>> >>> Guenter >>> >>> On Mon, Jul 22, 2019 at 10:30:48AM -0700, Guenter Roeck wrote: >>>> In bfq_insert_request(), bfqq is initialized with: >>>> bfqq = bfq_init_rq(rq); >>>> In bfq_init_rq(), we find: >>>> if (unlikely(!rq->elv.icq)) >>>> return NULL; >>>> Indeed, rq->elv.icq can be NULL if the memory allocation in >>>> create_task_io_context() failed. >>>> >>>> A comment in bfq_insert_request() suggests that bfqq is supposed to be >>>> non-NULL if 'at_head || blk_rq_is_passthrough(rq)' is false. Yet, as >>>> debugging and practical experience shows, this is not the case in the >>>> above situation. >>>> >>>> This results in the following crash. >>>> >>>> Unable to handle kernel NULL pointer dereference >>>> at virtual address 00000000000001b0 >>>> ... >>>> Call trace: >>>> bfq_setup_cooperator+0x44/0x134 >>>> bfq_insert_requests+0x10c/0x630 >>>> blk_mq_sched_insert_requests+0x60/0xb4 >>>> blk_mq_flush_plug_list+0x290/0x2d4 >>>> blk_flush_plug_list+0xe0/0x230 >>>> blk_finish_plug+0x30/0x40 >>>> generic_writepages+0x60/0x94 >>>> blkdev_writepages+0x24/0x30 >>>> do_writepages+0x74/0xac >>>> __filemap_fdatawrite_range+0x94/0xc8 >>>> file_write_and_wait_range+0x44/0xa0 >>>> blkdev_fsync+0x38/0x68 >>>> vfs_fsync_range+0x68/0x80 >>>> do_fsync+0x44/0x80 >>>> >>>> The problem is relatively easy to reproduce by running an image with >>>> failslab enabled, such as with: >>>> >>>> cd /sys/kernel/debug/failslab >>>> echo 10 > probability >>>> echo 300 > times >>>> >>>> Avoid the problem by checking if bfqq is NULL before using it. With the >>>> NULL check in place, requests with missing io context are queued >>>> immediately, and the crash is no longer seen. >>>> >>>> Fixes: 18e5a57d79878 ("block, bfq: postpone rq preparation to insert or merge") >>>> Reported-by: Hsin-Yi Wang <hsinyi@google.com> >>>> Cc: Hsin-Yi Wang <hsinyi@google.com> >>>> Cc: Nicolas Boichat <drinkcat@chromium.org> >>>> Cc: Doug Anderson <dianders@chromium.org> >>>> Signed-off-by: Guenter Roeck <linux@roeck-us.net> >>>> --- >>>> block/bfq-iosched.c | 2 +- >>>> 1 file changed, 1 insertion(+), 1 deletion(-) >>>> >>>> diff --git a/block/bfq-iosched.c b/block/bfq-iosched.c >>>> index 72860325245a..56f3f4227010 100644 >>>> --- a/block/bfq-iosched.c >>>> +++ b/block/bfq-iosched.c >>>> @@ -5417,7 +5417,7 @@ static void bfq_insert_request(struct blk_mq_hw_ctx *hctx, struct request *rq, >>>> >>>> spin_lock_irq(&bfqd->lock); >>>> bfqq = bfq_init_rq(rq); >>>> - if (at_head || blk_rq_is_passthrough(rq)) { >>>> + if (!bfqq || at_head || blk_rq_is_passthrough(rq)) { >>>> if (at_head) >>>> list_add(&rq->queuelist, &bfqd->dispatch); >>>> else >>>> -- >>>> 2.7.4 >>>> >
On 7/31/19 3:11 AM, Paolo Valente wrote: > > >> Il giorno 30 lug 2019, alle ore 15:35, Guenter Roeck <linux@roeck-us.net> ha scritto: >> >> On 7/30/19 1:55 AM, Paolo Valente wrote: >>> Hi Guenter, >>> sorry for the delay (Dolomiti's fault). >>> I didn't consider that rq->elv-icq might have been NULL also >>> because of OOM. Thanks for spotting this issue. >>> As for the other places where the return value of bfq_init_rq is used, >>> unfortunately I think they matter too. Those other places are related >>> to request merging, which is the alternative destiny of requests >>> (instead of being just inserted). But, regardless of whether a >>> request is to be merged or inserted, that request may be destined to a >>> bfq_queue (possibly merged with a request already in a bfq_queue), and >>> a NULL return value by bfq_init_rq leads to a crash. I guess you can >>> reproduce your failure also for the merge case, by generating >>> sequential, direct I/O with queue depth > 1, and of course by enabling >>> failslab. >> My assumption was that requests would only be merged if they are associated >> with the same io context. In that case, that IO context isn't reallocated >> with ioc_create_icq() but reused, and icq would thus never be NULL. >> I guess that assumption was wrong. > > I don't remember such a filtering. I had a look again, but didn't > find anything relevant. However, more competent people see these Me not either, when I had a closer look yesterday. My conclusion was that your analysis is correct. Thanks, Guenter > emails. Maybe someone can give us better advice. Otherwise, to stay > on the safe side, I'd propose to handle any possible NULL return. > > And I'll manage it, as per your request. > > Thanks, > Paolo > >> >>> If my considerations above are correct, do you want to propose a >>> complete fix yourself? >> >> Sure, I'll send an updated patch. >> >> Thanks, >> Guenter >> >>> Thanks, >>> Paolo >>>> Il giorno 28 lug 2019, alle ore 17:19, Guenter Roeck <linux@roeck-us.net> ha scritto: >>>> >>>> ping ... just in case this patch got lost in Paolo's queue. >>>> >>>> Guenter >>>> >>>> On Mon, Jul 22, 2019 at 10:30:48AM -0700, Guenter Roeck wrote: >>>>> In bfq_insert_request(), bfqq is initialized with: >>>>> bfqq = bfq_init_rq(rq); >>>>> In bfq_init_rq(), we find: >>>>> if (unlikely(!rq->elv.icq)) >>>>> return NULL; >>>>> Indeed, rq->elv.icq can be NULL if the memory allocation in >>>>> create_task_io_context() failed. >>>>> >>>>> A comment in bfq_insert_request() suggests that bfqq is supposed to be >>>>> non-NULL if 'at_head || blk_rq_is_passthrough(rq)' is false. Yet, as >>>>> debugging and practical experience shows, this is not the case in the >>>>> above situation. >>>>> >>>>> This results in the following crash. >>>>> >>>>> Unable to handle kernel NULL pointer dereference >>>>> at virtual address 00000000000001b0 >>>>> ... >>>>> Call trace: >>>>> bfq_setup_cooperator+0x44/0x134 >>>>> bfq_insert_requests+0x10c/0x630 >>>>> blk_mq_sched_insert_requests+0x60/0xb4 >>>>> blk_mq_flush_plug_list+0x290/0x2d4 >>>>> blk_flush_plug_list+0xe0/0x230 >>>>> blk_finish_plug+0x30/0x40 >>>>> generic_writepages+0x60/0x94 >>>>> blkdev_writepages+0x24/0x30 >>>>> do_writepages+0x74/0xac >>>>> __filemap_fdatawrite_range+0x94/0xc8 >>>>> file_write_and_wait_range+0x44/0xa0 >>>>> blkdev_fsync+0x38/0x68 >>>>> vfs_fsync_range+0x68/0x80 >>>>> do_fsync+0x44/0x80 >>>>> >>>>> The problem is relatively easy to reproduce by running an image with >>>>> failslab enabled, such as with: >>>>> >>>>> cd /sys/kernel/debug/failslab >>>>> echo 10 > probability >>>>> echo 300 > times >>>>> >>>>> Avoid the problem by checking if bfqq is NULL before using it. With the >>>>> NULL check in place, requests with missing io context are queued >>>>> immediately, and the crash is no longer seen. >>>>> >>>>> Fixes: 18e5a57d79878 ("block, bfq: postpone rq preparation to insert or merge") >>>>> Reported-by: Hsin-Yi Wang <hsinyi@google.com> >>>>> Cc: Hsin-Yi Wang <hsinyi@google.com> >>>>> Cc: Nicolas Boichat <drinkcat@chromium.org> >>>>> Cc: Doug Anderson <dianders@chromium.org> >>>>> Signed-off-by: Guenter Roeck <linux@roeck-us.net> >>>>> --- >>>>> block/bfq-iosched.c | 2 +- >>>>> 1 file changed, 1 insertion(+), 1 deletion(-) >>>>> >>>>> diff --git a/block/bfq-iosched.c b/block/bfq-iosched.c >>>>> index 72860325245a..56f3f4227010 100644 >>>>> --- a/block/bfq-iosched.c >>>>> +++ b/block/bfq-iosched.c >>>>> @@ -5417,7 +5417,7 @@ static void bfq_insert_request(struct blk_mq_hw_ctx *hctx, struct request *rq, >>>>> >>>>> spin_lock_irq(&bfqd->lock); >>>>> bfqq = bfq_init_rq(rq); >>>>> - if (at_head || blk_rq_is_passthrough(rq)) { >>>>> + if (!bfqq || at_head || blk_rq_is_passthrough(rq)) { >>>>> if (at_head) >>>>> list_add(&rq->queuelist, &bfqd->dispatch); >>>>> else >>>>> -- >>>>> 2.7.4 >>>>> >> > >
diff --git a/block/bfq-iosched.c b/block/bfq-iosched.c index 72860325245a..56f3f4227010 100644 --- a/block/bfq-iosched.c +++ b/block/bfq-iosched.c @@ -5417,7 +5417,7 @@ static void bfq_insert_request(struct blk_mq_hw_ctx *hctx, struct request *rq, spin_lock_irq(&bfqd->lock); bfqq = bfq_init_rq(rq); - if (at_head || blk_rq_is_passthrough(rq)) { + if (!bfqq || at_head || blk_rq_is_passthrough(rq)) { if (at_head) list_add(&rq->queuelist, &bfqd->dispatch); else
In bfq_insert_request(), bfqq is initialized with: bfqq = bfq_init_rq(rq); In bfq_init_rq(), we find: if (unlikely(!rq->elv.icq)) return NULL; Indeed, rq->elv.icq can be NULL if the memory allocation in create_task_io_context() failed. A comment in bfq_insert_request() suggests that bfqq is supposed to be non-NULL if 'at_head || blk_rq_is_passthrough(rq)' is false. Yet, as debugging and practical experience shows, this is not the case in the above situation. This results in the following crash. Unable to handle kernel NULL pointer dereference at virtual address 00000000000001b0 ... Call trace: bfq_setup_cooperator+0x44/0x134 bfq_insert_requests+0x10c/0x630 blk_mq_sched_insert_requests+0x60/0xb4 blk_mq_flush_plug_list+0x290/0x2d4 blk_flush_plug_list+0xe0/0x230 blk_finish_plug+0x30/0x40 generic_writepages+0x60/0x94 blkdev_writepages+0x24/0x30 do_writepages+0x74/0xac __filemap_fdatawrite_range+0x94/0xc8 file_write_and_wait_range+0x44/0xa0 blkdev_fsync+0x38/0x68 vfs_fsync_range+0x68/0x80 do_fsync+0x44/0x80 The problem is relatively easy to reproduce by running an image with failslab enabled, such as with: cd /sys/kernel/debug/failslab echo 10 > probability echo 300 > times Avoid the problem by checking if bfqq is NULL before using it. With the NULL check in place, requests with missing io context are queued immediately, and the crash is no longer seen. Fixes: 18e5a57d79878 ("block, bfq: postpone rq preparation to insert or merge") Reported-by: Hsin-Yi Wang <hsinyi@google.com> Cc: Hsin-Yi Wang <hsinyi@google.com> Cc: Nicolas Boichat <drinkcat@chromium.org> Cc: Doug Anderson <dianders@chromium.org> Signed-off-by: Guenter Roeck <linux@roeck-us.net> --- block/bfq-iosched.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)