From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754502Ab2GQCmf (ORCPT ); Mon, 16 Jul 2012 22:42:35 -0400 Received: from e23smtp04.au.ibm.com ([202.81.31.146]:51145 "EHLO e23smtp04.au.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754463Ab2GQCm2 (ORCPT ); Mon, 16 Jul 2012 22:42:28 -0400 Message-ID: <1342492936.2884.8.camel@ThinkPad-T420> Subject: [PATCH RESEND] Fix a dead loop in async_synchronize_full() From: Li Zhong To: paulmck@linux.vnet.ibm.com Cc: Dan Williams , Christian Kujau , Andrew Morton , LKML , arjan@linux.intel.com, Cong Wang , JBottomley@parallels.com, zhong@linux.vnet.ibm.com Date: Tue, 17 Jul 2012 10:42:16 +0800 In-Reply-To: <20120717015710.GA2438@linux.vnet.ibm.com> References: <1341817465.4579.5.camel@ThinkPad-T420> <20120711154232.165cbca9.akpm@linux-foundation.org> <1342086988.4091.44.camel@ThinkPad-T420> <20120717015710.GA2438@linux.vnet.ibm.com> Content-Type: text/plain; charset="UTF-8" X-Mailer: Evolution 3.2.3-0ubuntu6 Content-Transfer-Encoding: 7bit Mime-Version: 1.0 x-cbid: 12071616-9264-0000-0000-000001ED5558 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org resend it again with the email client fixed... in case it is needed 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 --- kernel/async.c | 13 +++++++++---- 1 file changed, 9 insertions(+), 4 deletions(-) diff --git a/kernel/async.c b/kernel/async.c index bd0c168..32d8dc9 100644 --- a/kernel/async.c +++ b/kernel/async.c @@ -86,6 +86,13 @@ 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); @@ -236,9 +243,7 @@ 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); @@ -258,7 +263,7 @@ 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 -- 1.7.9.5