jbd: Fix forever sleeping process in do_get_write_access() (2842bb20) · Commits · 戴 / test

In do_get_write_access() we wait on BH_Unshadow bit for buffer to get from shadow state. The waking code in journal_commit_transaction() has a bug because it does not issue a memory barrier after the buffer is moved from the shadow state and before wake_up_bit() is called. Thus a waitqueue check can happen before the buffer is actually moved from the shadow state and waiting process may never be woken. Fix the problem by issuing proper barrier. CC: stable@kernel.org Reported-by:

Tao Ma <boyu.mt@taobao.com> Signed-off-by:

Jan Kara <jack@suse.cz>

fs/jbd/commit.c

+7 −2

Original line number	Original line	Diff line number	Diff line
	@@ -722,8 +722,13 @@ wait_for_iobuf:
	required. */		required. */
	JBUFFER_TRACE(jh, "file as BJ_Forget");		JBUFFER_TRACE(jh, "file as BJ_Forget");
	journal_file_buffer(jh, commit_transaction, BJ_Forget);		journal_file_buffer(jh, commit_transaction, BJ_Forget);
	/* Wake up any transactions which were waiting for this		/*
	IO to complete */		* Wake up any transactions which were waiting for this
			* IO to complete. The barrier must be here so that changes
			* by journal_file_buffer() take effect before wake_up_bit()
			* does the waitqueue check.
			*/
			smp_mb();
	wake_up_bit(&bh->b_state, BH_Unshadow);		wake_up_bit(&bh->b_state, BH_Unshadow);
	JBUFFER_TRACE(jh, "brelse shadowed buffer");		JBUFFER_TRACE(jh, "brelse shadowed buffer");
	__brelse(bh);		__brelse(bh);

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