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 <cwi...@cwillu.com>
Reported-by: Luis Henriques <luis.henriq...@canonical.com>
Signed-off-by: Xiaotian Feng <dannyf...@tencent.com>
Cc: Ingo Molnar <mi...@redhat.com>
Cc: Peter Zijlstra <pet...@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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