| Message ID | 201805020714.FDD52145.OOJtOFVFSMLQFH@I-love.SAKURA.ne.jp (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
On Wed 02-05-18 07:14:51, Tetsuo Handa wrote: > >From 1b90d7f71d60e743c69cdff3ba41edd1f9f86f93 Mon Sep 17 00:00:00 2001 > From: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp> > Date: Wed, 2 May 2018 07:07:55 +0900 > Subject: [PATCH v2] bdi: wake up concurrent wb_shutdown() callers. > > syzbot is reporting hung tasks at wait_on_bit(WB_shutting_down) in > wb_shutdown() [1]. This seems to be because commit 5318ce7d46866e1d ("bdi: > Shutdown writeback on all cgwbs in cgwb_bdi_destroy()") forgot to call > wake_up_bit(WB_shutting_down) after clear_bit(WB_shutting_down). > > Introduce a helper function clear_and_wake_up_bit() and use it, in order > to avoid similar errors in future. > > [1] https://syzkaller.appspot.com/bug?id=b297474817af98d5796bc544e1bb806fc3da0e5e > > Signed-off-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp> > Reported-by: syzbot <syzbot+c0cf869505e03bdf1a24@syzkaller.appspotmail.com> > Fixes: 5318ce7d46866e1d ("bdi: Shutdown writeback on all cgwbs in cgwb_bdi_destroy()") > Cc: Tejun Heo <tj@kernel.org> > Cc: Jan Kara <jack@suse.cz> > Cc: Jens Axboe <axboe@fb.com> > Suggested-by: Linus Torvalds <torvalds@linux-foundation.org> Thanks for debugging this and for the fix Tetsuo! The patch looks good to me. You can add: Reviewed-by: Jan Kara <jack@suse.cz> Honza > --- > include/linux/wait_bit.h | 17 +++++++++++++++++ > mm/backing-dev.c | 2 +- > 2 files changed, 18 insertions(+), 1 deletion(-) > > diff --git a/include/linux/wait_bit.h b/include/linux/wait_bit.h > index 9318b21..2b0072f 100644 > --- a/include/linux/wait_bit.h > +++ b/include/linux/wait_bit.h > @@ -305,4 +305,21 @@ struct wait_bit_queue_entry { > __ret; \ > }) > > +/** > + * clear_and_wake_up_bit - clear a bit and wake up anyone waiting on that bit > + * > + * @bit: the bit of the word being waited on > + * @word: the word being waited on, a kernel virtual address > + * > + * You can use this helper if bitflags are manipulated atomically rather than > + * non-atomically under a lock. > + */ > +static inline void clear_and_wake_up_bit(int bit, void *word) > +{ > + clear_bit_unlock(bit, word); > + /* See wake_up_bit() for which memory barrier you need to use. */ > + smp_mb__after_atomic(); > + wake_up_bit(word, bit); > +} > + > #endif /* _LINUX_WAIT_BIT_H */ > diff --git a/mm/backing-dev.c b/mm/backing-dev.c > index 023190c..fa5e6d7 100644 > --- a/mm/backing-dev.c > +++ b/mm/backing-dev.c > @@ -383,7 +383,7 @@ static void wb_shutdown(struct bdi_writeback *wb) > * the barrier provided by test_and_clear_bit() above. > */ > smp_wmb(); > - clear_bit(WB_shutting_down, &wb->state); > + clear_and_wake_up_bit(WB_shutting_down, &wb->state); > } > > static void wb_exit(struct bdi_writeback *wb) > -- > 1.8.3.1
On 5/1/18 4:14 PM, Tetsuo Handa wrote: >>From 1b90d7f71d60e743c69cdff3ba41edd1f9f86f93 Mon Sep 17 00:00:00 2001 > From: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp> > Date: Wed, 2 May 2018 07:07:55 +0900 > Subject: [PATCH v2] bdi: wake up concurrent wb_shutdown() callers. > > syzbot is reporting hung tasks at wait_on_bit(WB_shutting_down) in > wb_shutdown() [1]. This seems to be because commit 5318ce7d46866e1d ("bdi: > Shutdown writeback on all cgwbs in cgwb_bdi_destroy()") forgot to call > wake_up_bit(WB_shutting_down) after clear_bit(WB_shutting_down). > > Introduce a helper function clear_and_wake_up_bit() and use it, in order > to avoid similar errors in future. Queued up, thanks Tetsuo!
diff --git a/include/linux/wait_bit.h b/include/linux/wait_bit.h index 9318b21..2b0072f 100644 --- a/include/linux/wait_bit.h +++ b/include/linux/wait_bit.h @@ -305,4 +305,21 @@ struct wait_bit_queue_entry { __ret; \ }) +/** + * clear_and_wake_up_bit - clear a bit and wake up anyone waiting on that bit + * + * @bit: the bit of the word being waited on + * @word: the word being waited on, a kernel virtual address + * + * You can use this helper if bitflags are manipulated atomically rather than + * non-atomically under a lock. + */ +static inline void clear_and_wake_up_bit(int bit, void *word) +{ + clear_bit_unlock(bit, word); + /* See wake_up_bit() for which memory barrier you need to use. */ + smp_mb__after_atomic(); + wake_up_bit(word, bit); +} + #endif /* _LINUX_WAIT_BIT_H */ diff --git a/mm/backing-dev.c b/mm/backing-dev.c index 023190c..fa5e6d7 100644 --- a/mm/backing-dev.c +++ b/mm/backing-dev.c @@ -383,7 +383,7 @@ static void wb_shutdown(struct bdi_writeback *wb) * the barrier provided by test_and_clear_bit() above. */ smp_wmb(); - clear_bit(WB_shutting_down, &wb->state); + clear_and_wake_up_bit(WB_shutting_down, &wb->state); } static void wb_exit(struct bdi_writeback *wb)