From: Theodore Ts'o Date: Mon, 1 Jul 2013 12:12:40 +0000 (-0400) Subject: jbd2: fix theoretical race in jbd2__journal_restart X-Git-Url: https://git.stricted.de/?a=commitdiff_plain;h=39c04153fda8c32e85b51c96eb5511a326ad7609;p=GitHub%2Fmoto-9609%2Fandroid_kernel_motorola_exynos9610.git jbd2: fix theoretical race in jbd2__journal_restart Once we decrement transaction->t_updates, if this is the last handle holding the transaction from closing, and once we release the t_handle_lock spinlock, it's possible for the transaction to commit and be released. In practice with normal kernels, this probably won't happen, since the commit happens in a separate kernel thread and it's unlikely this could all happen within the space of a few CPU cycles. On the other hand, with a real-time kernel, this could potentially happen, so save the tid found in transaction->t_tid before we release t_handle_lock. It would require an insane configuration, such as one where the jbd2 thread was set to a very high real-time priority, perhaps because a high priority real-time thread is trying to read or write to a file system. But some people who use real-time kernels have been known to do insane things, including controlling laser-wielding industrial robots. :-) Signed-off-by: "Theodore Ts'o" Cc: stable@vger.kernel.org --- diff --git a/fs/jbd2/transaction.c b/fs/jbd2/transaction.c index dd422e680418..383b0fbc6e19 100644 --- a/fs/jbd2/transaction.c +++ b/fs/jbd2/transaction.c @@ -652,10 +652,10 @@ int jbd2__journal_restart(handle_t *handle, int nblocks, gfp_t gfp_mask) } if (atomic_dec_and_test(&transaction->t_updates)) wake_up(&journal->j_wait_updates); + tid = transaction->t_tid; spin_unlock(&transaction->t_handle_lock); jbd_debug(2, "restarting handle %p\n", handle); - tid = transaction->t_tid; need_to_start = !tid_geq(journal->j_commit_request, tid); read_unlock(&journal->j_state_lock); if (need_to_start)