This is a note to let you know that I've just added the patch titled sched/cgroup: Fix/cleanup cgroup teardown/init to the 4.5-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary The filename of the patch is: sched-cgroup-fix-cleanup-cgroup-teardown-init.patch and it can be found in the queue-4.5 subdirectory. If you, or anyone else, feels it should not be added to the stable tree, please let <stable@xxxxxxxxxxxxxxx> know about it. >From 2f5177f0fd7e531b26d54633be62d1d4cb94621c Mon Sep 17 00:00:00 2001 From: Peter Zijlstra <peterz@xxxxxxxxxxxxx> Date: Wed, 16 Mar 2016 16:22:45 +0100 Subject: sched/cgroup: Fix/cleanup cgroup teardown/init From: Peter Zijlstra <peterz@xxxxxxxxxxxxx> commit 2f5177f0fd7e531b26d54633be62d1d4cb94621c upstream. The CPU controller hasn't kept up with the various changes in the whole cgroup initialization / destruction sequence, and commit: 2e91fa7f6d45 ("cgroup: keep zombies associated with their original cgroups") caused it to explode. The reason for this is that zombies do not inhibit css_offline() from being called, but do stall css_released(). Now we tear down the cfs_rq structures on css_offline() but zombies can run after that, leading to use-after-free issues. The solution is to move the tear-down to css_released(), which guarantees nobody (including no zombies) is still using our cgroup. Furthermore, a few simple cleanups are possible too. There doesn't appear to be any point to us using css_online() (anymore?) so fold that in css_alloc(). And since cgroup code guarantees an RCU grace period between css_released() and css_free() we can forgo using call_rcu() and free the stuff immediately. Suggested-by: Tejun Heo <tj@xxxxxxxxxx> Reported-by: Kazuki Yamaguchi <k@xxxxxx> Reported-by: Niklas Cassel <niklas.cassel@xxxxxxxx> Tested-by: Niklas Cassel <niklas.cassel@xxxxxxxx> Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx> Acked-by: Tejun Heo <tj@xxxxxxxxxx> Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx> Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx> Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx> Fixes: 2e91fa7f6d45 ("cgroup: keep zombies associated with their original cgroups") Link: http://lkml.kernel.org/r/20160316152245.GY6344@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> --- kernel/sched/core.c | 35 ++++++++++++++--------------------- 1 file changed, 14 insertions(+), 21 deletions(-) --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -7802,7 +7802,7 @@ void set_curr_task(int cpu, struct task_ /* task_group_lock serializes the addition/removal of task groups */ static DEFINE_SPINLOCK(task_group_lock); -static void free_sched_group(struct task_group *tg) +static void sched_free_group(struct task_group *tg) { free_fair_sched_group(tg); free_rt_sched_group(tg); @@ -7828,7 +7828,7 @@ struct task_group *sched_create_group(st return tg; err: - free_sched_group(tg); + sched_free_group(tg); return ERR_PTR(-ENOMEM); } @@ -7848,17 +7848,16 @@ void sched_online_group(struct task_grou } /* rcu callback to free various structures associated with a task group */ -static void free_sched_group_rcu(struct rcu_head *rhp) +static void sched_free_group_rcu(struct rcu_head *rhp) { /* now it should be safe to free those cfs_rqs */ - free_sched_group(container_of(rhp, struct task_group, rcu)); + sched_free_group(container_of(rhp, struct task_group, rcu)); } -/* Destroy runqueue etc associated with a task group */ void sched_destroy_group(struct task_group *tg) { /* wait for possible concurrent references to cfs_rqs complete */ - call_rcu(&tg->rcu, free_sched_group_rcu); + call_rcu(&tg->rcu, sched_free_group_rcu); } void sched_offline_group(struct task_group *tg) @@ -8319,31 +8318,26 @@ cpu_cgroup_css_alloc(struct cgroup_subsy if (IS_ERR(tg)) return ERR_PTR(-ENOMEM); + sched_online_group(tg, parent); + return &tg->css; } -static int cpu_cgroup_css_online(struct cgroup_subsys_state *css) +static void cpu_cgroup_css_released(struct cgroup_subsys_state *css) { struct task_group *tg = css_tg(css); - struct task_group *parent = css_tg(css->parent); - if (parent) - sched_online_group(tg, parent); - return 0; + sched_offline_group(tg); } static void cpu_cgroup_css_free(struct cgroup_subsys_state *css) { struct task_group *tg = css_tg(css); - sched_destroy_group(tg); -} - -static void cpu_cgroup_css_offline(struct cgroup_subsys_state *css) -{ - struct task_group *tg = css_tg(css); - - sched_offline_group(tg); + /* + * Relies on the RCU grace period between css_released() and this. + */ + sched_free_group(tg); } static void cpu_cgroup_fork(struct task_struct *task) @@ -8703,9 +8697,8 @@ static struct cftype cpu_files[] = { struct cgroup_subsys cpu_cgrp_subsys = { .css_alloc = cpu_cgroup_css_alloc, + .css_released = cpu_cgroup_css_released, .css_free = cpu_cgroup_css_free, - .css_online = cpu_cgroup_css_online, - .css_offline = cpu_cgroup_css_offline, .fork = cpu_cgroup_fork, .can_attach = cpu_cgroup_can_attach, .attach = cpu_cgroup_attach, Patches currently in stable-queue which might be from peterz@xxxxxxxxxxxxx are queue-4.5/sched-cgroup-fix-cleanup-cgroup-teardown-init.patch queue-4.5/x86-mce-avoid-using-object-after-free-in-genpool.patch -- To unsubscribe from this list: send the line "unsubscribe stable" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html