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| author | Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp> | 2018-05-02 01:07:55 +0300 |
|---|---|---|
| committer | Greg Kroah-Hartman <gregkh@linuxfoundation.org> | 2018-05-16 11:10:25 +0300 |
| commit | 6b5a99167a79f9a24e96eb2b0342505826534007 (patch) | |
| tree | 597b952a76373279fff6110d0c5bcb733e063de7 | |
| parent | 8c12bd91b59746140466e03d53049ae0c1b3f858 (diff) | |
| download | linux-6b5a99167a79f9a24e96eb2b0342505826534007.tar.xz | |
bdi: wake up concurrent wb_shutdown() callers.
commit 8236b0ae31c837d2b3a2565c5f8d77f637e824cc upstream.
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>
Reviewed-by: Jan Kara <jack@suse.cz>
Suggested-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
| -rw-r--r-- | include/linux/wait_bit.h | 17 | ||||
| -rw-r--r-- | mm/backing-dev.c | 2 |
2 files changed, 18 insertions, 1 deletions
diff --git a/include/linux/wait_bit.h b/include/linux/wait_bit.h index af0d495430d7..bc96d90bcafd 100644 --- a/include/linux/wait_bit.h +++ b/include/linux/wait_bit.h @@ -259,4 +259,21 @@ int wait_on_atomic_t(atomic_t *val, int (*action)(atomic_t *), unsigned mode) return out_of_line_wait_on_atomic_t(val, action, mode); } +/** + * 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 e19606bb41a0..dee049a0ec5b 100644 --- a/mm/backing-dev.c +++ b/mm/backing-dev.c @@ -381,7 +381,7 @@ 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) |