Messages in this thread Patch in this message | | | Date | Wed, 15 Jun 2011 17:15:09 -0700 | From | Greg KH <> | Subject | [12/91] jbd: Fix forever sleeping process in do_get_write_access() |
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2.6.32-longterm review patch. If anyone has any objections, please let us know.
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From: Jan Kara <jack@suse.cz>
commit 2842bb20eed2e25cde5114298edc62c8883a1d9a upstream.
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 <boyu.mt@taobao.com> Signed-off-by: Jan Kara <jack@suse.cz> Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
--- fs/jbd/commit.c | 9 +++++++-- 1 file changed, 7 insertions(+), 2 deletions(-)
--- a/fs/jbd/commit.c +++ b/fs/jbd/commit.c @@ -746,8 +746,13 @@ wait_for_iobuf: 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);
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