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sched, cgroup: Use exit hook to avoid use-after-free crash

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By not notifying the controller of the on-exit move back to
init_css_set, we fail to move the task out of the previous
cgroup's cfs_rq. This leads to an opportunity for a
cgroup-destroy to come in and free the cgroup (there are no
active tasks left in it after all) to which the not-quite dead
task is still enqueued.

Reported-by: Miklos Vajna <vmiklos@frugalware.org>
Fixed-by: Mike Galbraith <efault@gmx.de>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: <stable@kernel.org>
Cc: Mike Galbraith <efault@gmx.de>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
LKML-Reference: <1293206353.29444.205.camel@laptop>
This commit is contained in:
Peter Zijlstra 2011-01-19 12:26:11 +01:00 committed by Ingo Molnar
parent d7d8294415
commit 068c5cc5ac
1 changed files with 18 additions and 0 deletions
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18
kernel/sched.c
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@ -606,6 +606,9 @@ static inline struct task_group *task_group(struct task_struct *p)
struct task_group *tg;
struct cgroup_subsys_state *css;
if (p->flags & PF_EXITING)
return &root_task_group;
css = task_subsys_state_check(p, cpu_cgroup_subsys_id,
lockdep_is_held(&task_rq(p)->lock));
tg = container_of(css, struct task_group, css);
@ -8880,6 +8883,20 @@ cpu_cgroup_attach(struct cgroup_subsys *ss, struct cgroup *cgrp,
}
}
static void
cpu_cgroup_exit(struct cgroup_subsys *ss, struct task_struct *task)
{
/*
* cgroup_exit() is called in the copy_process() failure path.
* Ignore this case since the task hasn't ran yet, this avoids
* trying to poke a half freed task state from generic code.
*/
if (!(task->flags & PF_EXITING))
return;
sched_move_task(task);
}
#ifdef CONFIG_FAIR_GROUP_SCHED
static int cpu_shares_write_u64(struct cgroup *cgrp, struct cftype *cftype,
u64 shareval)
@ -8952,6 +8969,7 @@ struct cgroup_subsys cpu_cgroup_subsys = {
.destroy = cpu_cgroup_destroy,
.can_attach = cpu_cgroup_can_attach,
.attach = cpu_cgroup_attach,
.exit = cpu_cgroup_exit,
.populate = cpu_cgroup_populate,
.subsys_id = cpu_cgroup_subsys_id,
.early_init = 1,