From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753180Ab3FDWmf (ORCPT ); Tue, 4 Jun 2013 18:42:35 -0400 Received: from 1wt.eu ([62.212.114.60]:35466 "EHLO 1wt.eu" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752128Ab3FDWmX (ORCPT ); Tue, 4 Jun 2013 18:42:23 -0400 Message-Id: <20130604172131.637553911@1wt.eu> User-Agent: quilt/0.48-1 Date: Tue, 04 Jun 2013 19:22:02 +0200 From: Willy Tarreau To: linux-kernel@vger.kernel.org, stable@vger.kernel.org Cc: Li Zhong , Andrew Morton , Dan Williams , Christian Kujau , Cong Wang , Greg Kroah-Hartman , Willy Tarreau Subject: [ 032/184] Fix a dead loop in async_synchronize_full() In-Reply-To: <58df134a4b98edf5b0073e2e1e988fe6@local> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 2.6.32-longterm review patch. If anyone has any objections, please let me know. ------------------ From: Li Zhong [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: Willy Tarreau --- kernel/async.c | 13 +++++++++---- 1 file changed, 9 insertions(+), 4 deletions(-) diff --git a/kernel/async.c b/kernel/async.c index 27235f5..397a7c7 100644 --- a/kernel/async.c +++ b/kernel/async.c @@ -93,6 +93,13 @@ 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); @@ -248,9 +255,7 @@ 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); @@ -270,7 +275,7 @@ 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 -- 1.7.12.2.21.g234cd45.dirty