From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755555Ab2GFDvx (ORCPT ); Thu, 5 Jul 2012 23:51:53 -0400 Received: from trent.utfs.org ([94.185.90.103]:54890 "EHLO trent.utfs.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753056Ab2GFDvw (ORCPT ); Thu, 5 Jul 2012 23:51:52 -0400 Date: Thu, 5 Jul 2012 20:51:48 -0700 (PDT) From: Christian Kujau To: Li Zhong cc: LKML , arjan@linux.intel.com, "Paul E. McKenney" Subject: Re: [PATCH] Fix a dead loop in async_synchronize_full() In-Reply-To: <1341209044.5102.20.camel@ThinkPad-T420> Message-ID: References: <1341209044.5102.20.camel@ThinkPad-T420> User-Agent: Alpine 2.01 (DEB 1266 2009-07-14) MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII X-AV-Checked: ClamAV using ClamSMTP (127.0.0.1) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, 2 Jul 2012 at 14:04, Li Zhong wrote: > 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. This helps in my case[0], will this patch be included in -rc6? Thanks, Christian. [0] https://lists.ozlabs.org/pipermail/linuxppc-dev/2012-July/098922.html > 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 > --- > 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 > > -- > 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/ > -- BOFH excuse #192: runaway cat on system.