From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jeff Layton Subject: [PATCH v7 13/17] locks: skip deadlock detection on FL_FILE_PVT locks Date: Wed, 19 Mar 2014 16:45:57 -0400 Message-ID: <1395261961-10855-14-git-send-email-jlayton@redhat.com> References: <1395261961-10855-1-git-send-email-jlayton@redhat.com> Cc: linux-fsdevel@vger.kernel.org, bfields@fieldses.org To: viro@ZenIV.linux.org.uk Return-path: Received: from mail-qc0-f172.google.com ([209.85.216.172]:45177 "EHLO mail-qc0-f172.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755621AbaCSUq3 (ORCPT ); Wed, 19 Mar 2014 16:46:29 -0400 Received: by mail-qc0-f172.google.com with SMTP id i8so10663428qcq.31 for ; Wed, 19 Mar 2014 13:46:29 -0700 (PDT) In-Reply-To: <1395261961-10855-1-git-send-email-jlayton@redhat.com> Sender: linux-fsdevel-owner@vger.kernel.org List-ID: It's not really feasible to do deadlock detection with FL_FILE_PVT locks since they aren't owned by a single task, per-se. Deadlock detection also tends to be rather expensive so just skip it for these sorts of locks. Also, add a FIXME comment about adding more limited deadlock detection that just applies to ro -> rw upgrades, per Andy's request. Cc: Andy Lutomirski Signed-off-by: Jeff Layton --- fs/locks.c | 19 +++++++++++++++++-- 1 file changed, 17 insertions(+), 2 deletions(-) diff --git a/fs/locks.c b/fs/locks.c index f8cd6d7de161..8c5bc07c360f 100644 --- a/fs/locks.c +++ b/fs/locks.c @@ -564,7 +564,7 @@ static void __locks_insert_block(struct file_lock *blocker, BUG_ON(!list_empty(&waiter->fl_block)); waiter->fl_next = blocker; list_add_tail(&waiter->fl_block, &blocker->fl_block); - if (IS_POSIX(blocker)) + if (IS_POSIX(blocker) && !IS_FILE_PVT(blocker)) locks_insert_global_blocked(waiter); } @@ -757,8 +757,16 @@ EXPORT_SYMBOL(posix_test_lock); * Note: the above assumption may not be true when handling lock * requests from a broken NFS client. It may also fail in the presence * of tasks (such as posix threads) sharing the same open file table. - * * To handle those cases, we just bail out after a few iterations. + * + * For FL_FILE_PVT locks, the owner is the filp, not the files_struct. + * Because the owner is not even nominally tied to a thread of + * execution, the deadlock detection below can't reasonably work well. Just + * skip it for those. + * + * In principle, we could do a more limited deadlock detection on FL_FILE_PVT + * locks that just checks for the case where two tasks are attempting to + * upgrade from read to write locks on the same inode. */ #define MAX_DEADLK_ITERATIONS 10 @@ -781,6 +789,13 @@ static int posix_locks_deadlock(struct file_lock *caller_fl, { int i = 0; + /* + * This deadlock detector can't reasonably detect deadlocks with + * FL_FILE_PVT locks, since they aren't owned by a process, per-se. + */ + if (IS_FILE_PVT(caller_fl)) + return 0; + while ((block_fl = what_owner_is_waiting_for(block_fl))) { if (i++ > MAX_DEADLK_ITERATIONS) return 0; -- 1.8.5.3