From 229309caebe4508d650bb6d8f7d51f2b116f5bbd Mon Sep 17 00:00:00 2001 From: Jan Kara Date: Sun, 8 May 2011 19:09:53 -0400 Subject: jbd2: 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. Reported-by: Tao Ma Signed-off-by: Jan Kara Signed-off-by: "Theodore Ts'o" --- fs/jbd2/commit.c | 9 +++++++-- 1 file changed, 7 insertions(+), 2 deletions(-) (limited to 'fs/jbd2') diff --git a/fs/jbd2/commit.c b/fs/jbd2/commit.c index 6e28000a4b21..78c299218681 100644 --- a/fs/jbd2/commit.c +++ b/fs/jbd2/commit.c @@ -760,8 +760,13 @@ wait_for_iobuf: required. */ JBUFFER_TRACE(jh, "file as BJ_Forget"); jbd2_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 + * jbd2_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); -- cgit v1.2.1