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authorTetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>2018-05-02 01:07:55 +0300
committerJens Axboe <axboe@kernel.dk>2018-05-03 18:25:47 +0300
commit8236b0ae31c837d2b3a2565c5f8d77f637e824cc (patch)
treeb991aa5f1bea88908b05338a24f7db6c0f09fa2d
parent09a44ca2114737e0932257619c16a2b50c7807f1 (diff)
downloadlinux-8236b0ae31c837d2b3a2565c5f8d77f637e824cc.tar.xz
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 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>
-rw-r--r--include/linux/wait_bit.h17
-rw-r--r--mm/backing-dev.c2
2 files changed, 18 insertions, 1 deletions
diff --git a/include/linux/wait_bit.h b/include/linux/wait_bit.h
index 9318b2166439..2b0072fa5e92 100644
--- a/include/linux/wait_bit.h
+++ b/include/linux/wait_bit.h
@@ -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 */
diff --git a/mm/backing-dev.c b/mm/backing-dev.c
index 023190c69dce..fa5e6d7406d1 100644
--- a/mm/backing-dev.c
+++ b/mm/backing-dev.c
@@ -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)