2.6.32-longterm review patch. If anyone has any objections, please let us know.
------------------ From: Jan Kara <[email protected]> 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 <[email protected]> Signed-off-by: Jan Kara <[email protected]> Signed-off-by: Greg Kroah-Hartman <[email protected]> --- 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); _______________________________________________ stable mailing list [email protected] http://linux.kernel.org/mailman/listinfo/stable
