From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756393Ab0IRTL4 (ORCPT ); Sat, 18 Sep 2010 15:11:56 -0400 Received: from kroah.org ([198.145.64.141]:51761 "EHLO coco.kroah.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756023Ab0IRTCP (ORCPT ); Sat, 18 Sep 2010 15:02:15 -0400 X-Mailbox-Line: From gregkh@clark.site Sat Sep 18 12:00:01 2010 Message-Id: <20100918190001.216454704@clark.site> User-Agent: quilt/0.48-11.2 Date: Sat, 18 Sep 2010 11:59:02 -0700 From: Greg KH To: linux-kernel@vger.kernel.org, stable@kernel.org Cc: stable-review@kernel.org, torvalds@linux-foundation.org, akpm@linux-foundation.org, alan@lxorguk.ukuu.org.uk, Ingo Molnar , Peter Zijlstra , Greg KH , Oleg Nesterov , Mike Galbraith Subject: [098/123] sched: Make select_fallback_rq() cpuset friendly References: <20100918185724.290702750@clark.site> Content-Disposition: inline; filename=sched-make-select_fallback_rq-cpuset-friendly.patch In-Reply-To: <20100918190024.GA14388@kroah.com> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Oleg Nesterov commit 9084bb8246ea935b98320554229e2f371f7f52fa upstream Introduce cpuset_cpus_allowed_fallback() helper to fix the cpuset problems with select_fallback_rq(). It can be called from any context and can't use any cpuset locks including task_lock(). It is called when the task doesn't have online cpus in ->cpus_allowed but ttwu/etc must be able to find a suitable cpu. I am not proud of this patch. Everything which needs such a fat comment can't be good even if correct. But I'd prefer to not change the locking rules in the code I hardly understand, and in any case I believe this simple change make the code much more correct compared to deadlocks we currently have. Signed-off-by: Oleg Nesterov Signed-off-by: Peter Zijlstra LKML-Reference: <20100315091027.GA9155@redhat.com> Signed-off-by: Ingo Molnar Signed-off-by: Mike Galbraith Signed-off-by: Greg Kroah-Hartman --- include/linux/cpuset.h | 7 +++++++ kernel/cpuset.c | 42 ++++++++++++++++++++++++++++++++++++++++++ kernel/sched.c | 4 +--- 3 files changed, 50 insertions(+), 3 deletions(-) --- a/include/linux/cpuset.h +++ b/include/linux/cpuset.h @@ -21,6 +21,7 @@ extern int number_of_cpusets; /* How man extern int cpuset_init(void); extern void cpuset_init_smp(void); extern void cpuset_cpus_allowed(struct task_struct *p, struct cpumask *mask); +extern int cpuset_cpus_allowed_fallback(struct task_struct *p); extern nodemask_t cpuset_mems_allowed(struct task_struct *p); #define cpuset_current_mems_allowed (current->mems_allowed) void cpuset_init_current_mems_allowed(void); @@ -101,6 +102,12 @@ static inline void cpuset_cpus_allowed(s cpumask_copy(mask, cpu_possible_mask); } +static inline int cpuset_cpus_allowed_fallback(struct task_struct *p) +{ + cpumask_copy(&p->cpus_allowed, cpu_possible_mask); + return cpumask_any(cpu_active_mask); +} + static inline nodemask_t cpuset_mems_allowed(struct task_struct *p) { return node_possible_map; --- a/kernel/cpuset.c +++ b/kernel/cpuset.c @@ -2151,6 +2151,48 @@ void cpuset_cpus_allowed(struct task_str mutex_unlock(&callback_mutex); } +int cpuset_cpus_allowed_fallback(struct task_struct *tsk) +{ + const struct cpuset *cs; + int cpu; + + rcu_read_lock(); + cs = task_cs(tsk); + if (cs) + cpumask_copy(&tsk->cpus_allowed, cs->cpus_allowed); + rcu_read_unlock(); + + /* + * We own tsk->cpus_allowed, nobody can change it under us. + * + * But we used cs && cs->cpus_allowed lockless and thus can + * race with cgroup_attach_task() or update_cpumask() and get + * the wrong tsk->cpus_allowed. However, both cases imply the + * subsequent cpuset_change_cpumask()->set_cpus_allowed_ptr() + * which takes task_rq_lock(). + * + * If we are called after it dropped the lock we must see all + * changes in tsk_cs()->cpus_allowed. Otherwise we can temporary + * set any mask even if it is not right from task_cs() pov, + * the pending set_cpus_allowed_ptr() will fix things. + */ + + cpu = cpumask_any_and(&tsk->cpus_allowed, cpu_active_mask); + if (cpu >= nr_cpu_ids) { + /* + * Either tsk->cpus_allowed is wrong (see above) or it + * is actually empty. The latter case is only possible + * if we are racing with remove_tasks_in_empty_cpuset(). + * Like above we can temporary set any mask and rely on + * set_cpus_allowed_ptr() as synchronization point. + */ + cpumask_copy(&tsk->cpus_allowed, cpu_possible_mask); + cpu = cpumask_any(cpu_active_mask); + } + + return cpu; +} + void cpuset_init_current_mems_allowed(void) { nodes_setall(current->mems_allowed); --- a/kernel/sched.c +++ b/kernel/sched.c @@ -2353,9 +2353,7 @@ static int select_fallback_rq(int cpu, s /* No more Mr. Nice Guy. */ if (unlikely(dest_cpu >= nr_cpu_ids)) { - cpumask_copy(&p->cpus_allowed, cpu_possible_mask); - dest_cpu = cpumask_any(cpu_active_mask); - + dest_cpu = cpuset_cpus_allowed_fallback(p); /* * Don't tell them about moving exiting tasks or * kernel threads (both mm NULL), since they never