bdi: wake up concurrent wb_shutdown() callers. (8236b0ae) · Commits · 戴 / test

syzbot is reporting hung tasks at wait_on_bit(WB_shutting_down) in wb_shutdown() [1]. This seems to be because commit ("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: ("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>

include/linux/wait_bit.h

+17 −0

Original line number	Original line	Diff line number	Diff line
	@@ -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 */

mm/backing-dev.c

+1 −1

Original line number	Original line	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.		* 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)

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