Return-Path: Message-Id: <20130813155834.036573610@goodmis.org> Date: Tue, 13 Aug 2013 11:58:00 -0400 From: Steven Rostedt To: linux-kernel@vger.kernel.org, stable@vger.kernel.org Cc: "Theodore Tso" Subject: [66/88] jbd2: fix theoretical race in jbd2__journal_restart References: <20130813155654.069291373@goodmis.org> Content-Disposition: inline; filename=0066-jbd2-fix-theoretical-race-in-jbd2__journal_restart.patch Sender: linux-kernel-owner@vger.kernel.org List-ID: 3.6.11.7-rc1 stable review patch. If anyone has any objections, please let me know. ------------------ From: Theodore Ts'o [ Upstream commit 39c04153fda8c32e85b51c96eb5511a326ad7609 ] 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 Signed-off-by: Steven Rostedt --- fs/jbd2/transaction.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/fs/jbd2/transaction.c b/fs/jbd2/transaction.c index 9427cf1..718fe8f 100644 --- a/fs/jbd2/transaction.c +++ b/fs/jbd2/transaction.c @@ -499,10 +499,10 @@ int jbd2__journal_restart(handle_t *handle, int nblocks, gfp_t gfp_mask) &transaction->t_outstanding_credits); 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) -- 1.7.10.4