sched/autogroup: Fix race with task_groups list

In autogroup_create(), a tg is allocated and added to the task_groups
list. If CONFIG_RT_GROUP_SCHED is set, this tg is then modified while on
the list, without locking. This can race with someone walking the list,
like __enable_runtime() during CPU unplug, and result in a use-after-free
bug.

To fix this, move sched_online_group(), which adds the tg to the list,
to the end of the autogroup_create() function after the modification.

Signed-off-by: Gerald Schaefer <gerald.schaefer@de.ibm.com>
Signed-off-by: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/1369411669-46971-2-git-send-email-gerald.schaefer@de.ibm.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>

diff --git a/kernel/sched/auto_group.c b/kernel/sched/auto_group.c
index 64de5f8b0c9ed654ec475c2cae33fe539a1d43ca..4a073539c58e69992ed2133a73444ceffc9cd3fa 100644 (file)
--- a/kernel/sched/auto_group.c
+++ b/kernel/sched/auto_group.c
@@ -77,8 +77,6 @@ static inline struct autogroup *autogroup_create(void)
        if (IS_ERR(tg))
                goto out_free;
 
-       sched_online_group(tg, &root_task_group);
-
        kref_init(&ag->kref);
        init_rwsem(&ag->lock);
        ag->id = atomic_inc_return(&autogroup_seq_nr);
@@ -98,6 +96,7 @@ static inline struct autogroup *autogroup_create(void)
 #endif
        tg->autogroup = ag;
 
+       sched_online_group(tg, &root_task_group);
        return ag;
 
 out_free: