Messages in this thread Patch in this message | | | From | Xiaotian Feng <> | Subject | [PATCH] sched, autogroup: fix kernel crashes caused by runtime disable autogroup | Date | Fri, 19 Oct 2012 16:36:10 +0800 |
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There's a regression from commit 800d4d30, in autogroup_move_group()
p->signal->autogroup = autogroup_kref_get(ag);
if (!ACCESS_ONCE(sysctl_sched_autogroup_enabled)) goto out; ... out: autogroup_kref_put(prev);
So kernel changed p's autogroup to ag, but never sched_move_task(p). Then previous autogroup of p is released, which may release task_group related with p. After commit 8323f26ce, p->sched_task_group might point to this stale value, and thus caused kernel crashes.
This is very easy to reproduce, add "kernel.sched_autogroup_enabled = 0" to your /etc/sysctl.conf, your system will never boot up. It is not reasonable to put the sysctl enabled check in autogroup_move_group(), kernel should check it before autogroup_create in sched_autogroup_create_attach().
Reported-by: cwillu <cwillu@cwillu.com> Reported-by: Luis Henriques <luis.henriques@canonical.com> Signed-off-by: Xiaotian Feng <dannyfeng@tencent.com> Cc: Ingo Molnar <mingo@redhat.com> Cc: Peter Zijlstra <peterz@infradead.org> --- kernel/sched/auto_group.c | 10 +++++----- 1 file changed, 5 insertions(+), 5 deletions(-)
diff --git a/kernel/sched/auto_group.c b/kernel/sched/auto_group.c index 0984a21..ac62415 100644 --- a/kernel/sched/auto_group.c +++ b/kernel/sched/auto_group.c @@ -143,15 +143,11 @@ autogroup_move_group(struct task_struct *p, struct autogroup *ag) p->signal->autogroup = autogroup_kref_get(ag); - if (!ACCESS_ONCE(sysctl_sched_autogroup_enabled)) - goto out; - t = p; do { sched_move_task(t); } while_each_thread(p, t); -out: unlock_task_sighand(p, &flags); autogroup_kref_put(prev); } @@ -159,8 +155,12 @@ out: /* Allocates GFP_KERNEL, cannot be called under any spinlock */ void sched_autogroup_create_attach(struct task_struct *p) { - struct autogroup *ag = autogroup_create(); + struct autogroup *ag; + + if (!ACCESS_ONCE(sysctl_sched_autogroup_enabled)) + return; + ag = autogroup_create(); autogroup_move_group(p, ag); /* drop extra reference added by autogroup_create() */ autogroup_kref_put(ag); -- 1.7.9.5
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