Commit 2842bb20 authored May 05, 2011 by Jan Kara

jbd: Fix forever sleeping process in do_get_write_access()



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>

parent 4e299c1d

fs/jbd/commit.c

+7 −2

Original line number	Diff line number	Diff line
		@@ -722,8 +722,13 @@ void journal_commit_transaction(journal_t *journal)
		required. */
		JBUFFER_TRACE(jh, "file as 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);
		JBUFFER_TRACE(jh, "brelse shadowed buffer");
		__brelse(bh);