From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755423AbeBOKeA (ORCPT ); Thu, 15 Feb 2018 05:34:00 -0500 Received: from mail-wr0-f196.google.com ([209.85.128.196]:43225 "EHLO mail-wr0-f196.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755304AbeBOKd5 (ORCPT ); Thu, 15 Feb 2018 05:33:57 -0500 X-Google-Smtp-Source: AH8x226P/xhB+1QO/GaVHjJDlJvud/KWUa98HGQoU9Sct4sgNWqKMotGGhyElptE87oxCGon9w52UA== Date: Thu, 15 Feb 2018 11:33:53 +0100 From: Juri Lelli To: Mathieu Poirier Cc: Peter Zijlstra , Li Zefan , Ingo Molnar , Steven Rostedt , Claudio Scordino , Daniel Bristot de Oliveira , Tommaso Cucinotta , "luca.abeni" , cgroups@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH V3 04/10] sched/core: Prevent race condition between cpuset and __sched_setscheduler() Message-ID: <20180215103353.GX12979@localhost.localdomain> References: <1518553967-20656-1-git-send-email-mathieu.poirier@linaro.org> <1518553967-20656-5-git-send-email-mathieu.poirier@linaro.org> <20180214103639.GR12979@localhost.localdomain> <20180214104935.GS12979@localhost.localdomain> <20180214112721.GT12979@localhost.localdomain> <20180214163145.GV12979@localhost.localdomain> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20180214163145.GV12979@localhost.localdomain> User-Agent: Mutt/1.9.1 (2017-09-22) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 14/02/18 17:31, Juri Lelli wrote: [...] > Still grabbing it is a no-go, as do_sched_setscheduler calls > sched_setscheduler from inside an RCU read-side critical section. I was then actually thinking that trylocking might do.. not sure however if failing with -EBUSY in the contended case is feasible (and about the general uglyness of the solution :/). --->8--- include/linux/cpuset.h | 4 ++-- kernel/cgroup/cpuset.c | 6 +++--- kernel/sched/core.c | 4 +++- 3 files changed, 8 insertions(+), 6 deletions(-) diff --git a/include/linux/cpuset.h b/include/linux/cpuset.h index 4bbb3f5a3020..53c3f4e13cb0 100644 --- a/include/linux/cpuset.h +++ b/include/linux/cpuset.h @@ -55,7 +55,7 @@ extern void cpuset_init_smp(void); extern void cpuset_force_rebuild(void); extern void cpuset_update_active_cpus(void); extern void cpuset_wait_for_hotplug(void); -extern void cpuset_lock(void); +extern int cpuset_trylock(void); extern void cpuset_unlock(void); extern void cpuset_cpus_allowed(struct task_struct *p, struct cpumask *mask); extern void cpuset_cpus_allowed_fallback(struct task_struct *p); @@ -178,7 +178,7 @@ static inline void cpuset_update_active_cpus(void) static inline void cpuset_wait_for_hotplug(void) { } -static inline void cpuset_lock(void) { } +static inline int cpuset_trylock(void) { return 1; } static inline void cpuset_unlock(void) { } diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c index 41f8391640e6..995aac5b032d 100644 --- a/kernel/cgroup/cpuset.c +++ b/kernel/cgroup/cpuset.c @@ -2410,11 +2410,11 @@ void __init cpuset_init_smp(void) } /** - * cpuset_lock - Grab the cpuset_mutex from another subsysytem + * cpuset_trylock - Try to grab the cpuset_mutex atomically from another subsytem */ -void cpuset_lock(void) +int cpuset_trylock(void) { - mutex_lock(&cpuset_mutex); + return mutex_trylock(&cpuset_mutex); } /** diff --git a/kernel/sched/core.c b/kernel/sched/core.c index 0d8badcf1f0f..b491b406a835 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -4180,7 +4180,8 @@ static int __sched_setscheduler(struct task_struct *p, * domains can be rebuilt or modified while operations like DL * admission checks are carried out. */ - cpuset_lock(); + if (!cpuset_trylock()) + return -EBUSY; /* * Make sure no PI-waiters arrive (or leave) while we are @@ -4312,6 +4313,7 @@ static int __sched_setscheduler(struct task_struct *p, /* Avoid rq from going away on us: */ preempt_disable(); task_rq_unlock(rq, p, &rf); + cpuset_unlock(); if (pi) rt_mutex_adjust_pi(p); From mboxrd@z Thu Jan 1 00:00:00 1970 From: Juri Lelli Subject: Re: [PATCH V3 04/10] sched/core: Prevent race condition between cpuset and __sched_setscheduler() Date: Thu, 15 Feb 2018 11:33:53 +0100 Message-ID: <20180215103353.GX12979@localhost.localdomain> References: <1518553967-20656-1-git-send-email-mathieu.poirier@linaro.org> <1518553967-20656-5-git-send-email-mathieu.poirier@linaro.org> <20180214103639.GR12979@localhost.localdomain> <20180214104935.GS12979@localhost.localdomain> <20180214112721.GT12979@localhost.localdomain> <20180214163145.GV12979@localhost.localdomain> Mime-Version: 1.0 Return-path: Content-Disposition: inline In-Reply-To: <20180214163145.GV12979-bi+AKbBUZKY6gyzm1THtWbp2dZbC/Bob@public.gmane.org> Sender: cgroups-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org List-ID: Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: Mathieu Poirier Cc: Peter Zijlstra , Li Zefan , Ingo Molnar , Steven Rostedt , Claudio Scordino , Daniel Bristot de Oliveira , Tommaso Cucinotta , "luca.abeni" , cgroups-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org On 14/02/18 17:31, Juri Lelli wrote: [...] > Still grabbing it is a no-go, as do_sched_setscheduler calls > sched_setscheduler from inside an RCU read-side critical section. I was then actually thinking that trylocking might do.. not sure however if failing with -EBUSY in the contended case is feasible (and about the general uglyness of the solution :/). --->8--- include/linux/cpuset.h | 4 ++-- kernel/cgroup/cpuset.c | 6 +++--- kernel/sched/core.c | 4 +++- 3 files changed, 8 insertions(+), 6 deletions(-) diff --git a/include/linux/cpuset.h b/include/linux/cpuset.h index 4bbb3f5a3020..53c3f4e13cb0 100644 --- a/include/linux/cpuset.h +++ b/include/linux/cpuset.h @@ -55,7 +55,7 @@ extern void cpuset_init_smp(void); extern void cpuset_force_rebuild(void); extern void cpuset_update_active_cpus(void); extern void cpuset_wait_for_hotplug(void); -extern void cpuset_lock(void); +extern int cpuset_trylock(void); extern void cpuset_unlock(void); extern void cpuset_cpus_allowed(struct task_struct *p, struct cpumask *mask); extern void cpuset_cpus_allowed_fallback(struct task_struct *p); @@ -178,7 +178,7 @@ static inline void cpuset_update_active_cpus(void) static inline void cpuset_wait_for_hotplug(void) { } -static inline void cpuset_lock(void) { } +static inline int cpuset_trylock(void) { return 1; } static inline void cpuset_unlock(void) { } diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c index 41f8391640e6..995aac5b032d 100644 --- a/kernel/cgroup/cpuset.c +++ b/kernel/cgroup/cpuset.c @@ -2410,11 +2410,11 @@ void __init cpuset_init_smp(void) } /** - * cpuset_lock - Grab the cpuset_mutex from another subsysytem + * cpuset_trylock - Try to grab the cpuset_mutex atomically from another subsytem */ -void cpuset_lock(void) +int cpuset_trylock(void) { - mutex_lock(&cpuset_mutex); + return mutex_trylock(&cpuset_mutex); } /** diff --git a/kernel/sched/core.c b/kernel/sched/core.c index 0d8badcf1f0f..b491b406a835 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -4180,7 +4180,8 @@ static int __sched_setscheduler(struct task_struct *p, * domains can be rebuilt or modified while operations like DL * admission checks are carried out. */ - cpuset_lock(); + if (!cpuset_trylock()) + return -EBUSY; /* * Make sure no PI-waiters arrive (or leave) while we are @@ -4312,6 +4313,7 @@ static int __sched_setscheduler(struct task_struct *p, /* Avoid rq from going away on us: */ preempt_disable(); task_rq_unlock(rq, p, &rf); + cpuset_unlock(); if (pi) rt_mutex_adjust_pi(p);