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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 5318ce7d46 ("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: 5318ce7d46 ("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>
This commit is contained in:
Tetsuo Handa 2018-05-02 07:07:55 +09:00 committed by Jens Axboe
parent 09a44ca211
commit 8236b0ae31
2 changed files with 18 additions and 1 deletions
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17
include/linux/wait_bit.h
View File

@ -305,4 +305,21 @@ do { \
__ret; \ __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 */ #endif /* _LINUX_WAIT_BIT_H */

2
mm/backing-dev.c
View File

@ -383,7 +383,7 @@ static void wb_shutdown(struct bdi_writeback *wb)
* the barrier provided by test_and_clear_bit() above. * the barrier provided by test_and_clear_bit() above.
*/ */
smp_wmb(); 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) static void wb_exit(struct bdi_writeback *wb)