| From 8236b0ae31c837d2b3a2565c5f8d77f637e824cc 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: bdi: wake up concurrent wb_shutdown() callers. |
| |
| From: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp> |
| |
| 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> |
| |
| --- |
| include/linux/wait_bit.h | 17 +++++++++++++++++ |
| mm/backing-dev.c | 2 +- |
| 2 files changed, 18 insertions(+), 1 deletion(-) |
| |
| --- 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 |
| 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 */ |
| --- a/mm/backing-dev.c |
| +++ b/mm/backing-dev.c |
| @@ -381,7 +381,7 @@ static void wb_shutdown(struct bdi_write |
| * 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) |
