Donate to e Foundation | Murena handsets with /e/OS | Own a part of Murena! Learn more

Commit 8236b0ae authored by Tetsuo Handa's avatar Tetsuo Handa Committed by Jens Axboe
Browse files

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 5318ce7d ("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: default avatarTetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Reported-by: default avatarsyzbot <syzbot+c0cf869505e03bdf1a24@syzkaller.appspotmail.com>
Fixes: 5318ce7d ("bdi: Shutdown writeback on all cgwbs in cgwb_bdi_destroy()")
Cc: Tejun Heo <tj@kernel.org>
Reviewed-by: default avatarJan Kara <jack@suse.cz>
Suggested-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: default avatarJens Axboe <axboe@kernel.dk>
parent 09a44ca2

include/linux/wait_bit.h

+17 −0
Original line number Diff line number Diff line
@@ -305,4 +305,21 @@ do { \ 
	__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 */

mm/backing-dev.c

+1 −1
Original line number Diff line number Diff line
@@ -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)