Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932164AbaBEUGS (ORCPT ); Wed, 5 Feb 2014 15:06:18 -0500 Received: from mail1.windriver.com ([147.11.146.13]:48232 "EHLO mail1.windriver.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754720AbaBEUF4 (ORCPT ); Wed, 5 Feb 2014 15:05:56 -0500 From: Paul Gortmaker To: , CC: Li Zhong , Andrew Morton , Dan Williams , Christian Kujau , Cong Wang , Greg Kroah-Hartman , Paul Gortmaker Subject: [v2.6.34-stable 095/213] Fix a dead loop in async_synchronize_full() Date: Wed, 5 Feb 2014 15:00:50 -0500 Message-ID: <1391630568-49251-96-git-send-email-paul.gortmaker@windriver.com> X-Mailer: git-send-email 1.8.5.2 In-Reply-To: <1391630568-49251-1-git-send-email-paul.gortmaker@windriver.com> References: <1391630568-49251-1-git-send-email-paul.gortmaker@windriver.com> MIME-Version: 1.0 Content-Type: text/plain Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Li Zhong ------------------- This is a commit scheduled for the next v2.6.34 longterm release. http://git.kernel.org/?p=linux/kernel/git/paulg/longterm-queue-2.6.34.git If you see a problem with using this for longterm, please comment. ------------------- [commit 45516ddc16abc923104d78bb3eb772ac0a09e33e in v3.0.44 - paulg ] [Fixed upstream by commits 2955b47d2c1983998a8c5915cb96884e67f7cb53 and a4683487f90bfe3049686fc5c566bdc1ad03ace6 from Dan Williams, but they are much more intrusive than this tiny fix, according to Andrew - gregkh] This patch tries to fix a dead loop in async_synchronize_full(), which could be seen when preemption is disabled on a single cpu machine. void async_synchronize_full(void) { do { async_synchronize_cookie(next_cookie); } while (!list_empty(&async_running) || ! list_empty(&async_pending)); } async_synchronize_cookie() calls async_synchronize_cookie_domain() with &async_running as the default domain to synchronize. However, there might be some works in the async_pending list from other domains. On a single cpu system, without preemption, there is no chance for the other works to finish, so async_synchronize_full() enters a dead loop. It seems async_synchronize_full() wants to synchronize all entries in all running lists(domains), so maybe we could just check the entry_count to know whether all works are finished. Currently, async_synchronize_cookie_domain() expects a non-NULL running list ( if NULL, there would be NULL pointer dereference ), so maybe a NULL pointer could be used as an indication for the functions to synchronize all works in all domains. Reported-by: Paul E. McKenney Signed-off-by: Li Zhong Tested-by: Paul E. McKenney Tested-by: Christian Kujau Cc: Andrew Morton Cc: Dan Williams Cc: Christian Kujau Cc: Andrew Morton Cc: Cong Wang Signed-off-by: Greg Kroah-Hartman Signed-off-by: Paul Gortmaker --- kernel/async.c | 13 +++++++++---- 1 file changed, 9 insertions(+), 4 deletions(-) diff --git a/kernel/async.c b/kernel/async.c index 15319d6c18fe..b640ffc3f5a1 100644 --- a/kernel/async.c +++ b/kernel/async.c @@ -94,6 +94,13 @@ static async_cookie_t __lowest_in_progress(struct list_head *running) { struct async_entry *entry; + if (!running) { /* just check the entry count */ + if (atomic_read(&entry_count)) + return 0; /* smaller than any cookie */ + else + return next_cookie; + } + if (!list_empty(running)) { entry = list_first_entry(running, struct async_entry, list); @@ -249,9 +256,7 @@ EXPORT_SYMBOL_GPL(async_schedule_domain); */ void async_synchronize_full(void) { - do { - async_synchronize_cookie(next_cookie); - } while (!list_empty(&async_running) || !list_empty(&async_pending)); + async_synchronize_cookie_domain(next_cookie, NULL); } EXPORT_SYMBOL_GPL(async_synchronize_full); @@ -271,7 +276,7 @@ EXPORT_SYMBOL_GPL(async_synchronize_full_domain); /** * async_synchronize_cookie_domain - synchronize asynchronous function calls within a certain domain with cookie checkpointing * @cookie: async_cookie_t to use as checkpoint - * @running: running list to synchronize on + * @running: running list to synchronize on, NULL indicates all lists * * This function waits until all asynchronous function calls for the * synchronization domain specified by the running list @list submitted -- 1.8.5.2 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/