Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752909AbZIXAEa (ORCPT ); Wed, 23 Sep 2009 20:04:30 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752878AbZIXAE1 (ORCPT ); Wed, 23 Sep 2009 20:04:27 -0400 Received: from smtp231.iad.emailsrvr.com ([207.97.245.231]:35608 "EHLO smtp231.iad.emailsrvr.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752258AbZIXAES (ORCPT ); Wed, 23 Sep 2009 20:04:18 -0400 From: Oren Laadan To: Andrew Morton Cc: Linus Torvalds , containers@lists.linux-foundation.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, linux-api@vger.kernel.org, Serge Hallyn , Ingo Molnar , Pavel Emelyanov , Matt Helsley , Cedric Le Goater , Paul Menage , Li Zefan , "Rafael J. Wysocki" , Pavel Machek , linux-pm@lists.linux-foundation.org Subject: [PATCH v18 05/80] cgroup freezer: Fix buggy resume test for tasks frozen with cgroup freezer Date: Wed, 23 Sep 2009 19:50:45 -0400 Message-Id: <1253749920-18673-6-git-send-email-orenl@librato.com> X-Mailer: git-send-email 1.6.0.4 In-Reply-To: <1253749920-18673-1-git-send-email-orenl@librato.com> References: <1253749920-18673-1-git-send-email-orenl@librato.com> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 4215 Lines: 113 From: Matt Helsley When the cgroup freezer is used to freeze tasks we do not want to thaw those tasks during resume. Currently we test the cgroup freezer state of the resuming tasks to see if the cgroup is FROZEN. If so then we don't thaw the task. However, the FREEZING state also indicates that the task should remain frozen. This also avoids a problem pointed out by Oren Ladaan: the freezer state transition from FREEZING to FROZEN is updated lazily when userspace reads or writes the freezer.state file in the cgroup filesystem. This means that resume will thaw tasks in cgroups which should be in the FROZEN state if there is no read/write of the freezer.state file to trigger this transition before suspend. NOTE: Another "simple" solution would be to always update the cgroup freezer state during resume. However it's a bad choice for several reasons: Updating the cgroup freezer state is somewhat expensive because it requires walking all the tasks in the cgroup and checking if they are each frozen. Worse, this could easily make resume run in N^2 time where N is the number of tasks in the cgroup. Finally, updating the freezer state from this code path requires trickier locking because of the way locks must be ordered. Instead of updating the freezer state we rely on the fact that lazy updates only manage the transition from FREEZING to FROZEN. We know that a cgroup with the FREEZING state may actually be FROZEN so test for that state too. This makes sense in the resume path even for partially-frozen cgroups -- those that really are FREEZING but not FROZEN. Reported-by: Oren Ladaan Signed-off-by: Matt Helsley Cc: Cedric Le Goater Cc: Paul Menage Cc: Li Zefan Cc: Rafael J. Wysocki Cc: Pavel Machek Cc: linux-pm@lists.linux-foundation.org Seems like a candidate for -stable. --- include/linux/freezer.h | 7 +++++-- kernel/cgroup_freezer.c | 9 ++++++--- kernel/power/process.c | 2 +- 3 files changed, 12 insertions(+), 6 deletions(-) diff --git a/include/linux/freezer.h b/include/linux/freezer.h index 5a361f8..da7e52b 100644 --- a/include/linux/freezer.h +++ b/include/linux/freezer.h @@ -64,9 +64,12 @@ extern bool freeze_task(struct task_struct *p, bool sig_only); extern void cancel_freezing(struct task_struct *p); #ifdef CONFIG_CGROUP_FREEZER -extern int cgroup_frozen(struct task_struct *task); +extern int cgroup_freezing_or_frozen(struct task_struct *task); #else /* !CONFIG_CGROUP_FREEZER */ -static inline int cgroup_frozen(struct task_struct *task) { return 0; } +static inline int cgroup_freezing_or_frozen(struct task_struct *task) +{ + return 0; +} #endif /* !CONFIG_CGROUP_FREEZER */ /* diff --git a/kernel/cgroup_freezer.c b/kernel/cgroup_freezer.c index fb249e2..765e2c1 100644 --- a/kernel/cgroup_freezer.c +++ b/kernel/cgroup_freezer.c @@ -47,17 +47,20 @@ static inline struct freezer *task_freezer(struct task_struct *task) struct freezer, css); } -int cgroup_frozen(struct task_struct *task) +int cgroup_freezing_or_frozen(struct task_struct *task) { struct freezer *freezer; enum freezer_state state; task_lock(task); freezer = task_freezer(task); - state = freezer->state; + if (!freezer->css.cgroup->parent) + state = CGROUP_THAWED; /* root cgroup can't be frozen */ + else + state = freezer->state; task_unlock(task); - return state == CGROUP_FROZEN; + return (state == CGROUP_FREEZING) || (state == CGROUP_FROZEN); } /* diff --git a/kernel/power/process.c b/kernel/power/process.c index da2072d..3728d4c 100644 --- a/kernel/power/process.c +++ b/kernel/power/process.c @@ -138,7 +138,7 @@ static void thaw_tasks(bool nosig_only) if (nosig_only && should_send_signal(p)) continue; - if (cgroup_frozen(p)) + if (cgroup_freezing_or_frozen(p)) continue; thaw_process(p); -- 1.6.0.4 -- 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/