path: root/kernel
diff options
authorDaisuke Nishimura <nishimura@mxp.nes.nec.co.jp>2013-09-10 18:16:36 +0900
committerIngo Molnar <mingo@kernel.org>2013-09-12 19:14:14 +0200
commit6c9a27f5da9609fca46cb2b183724531b48f71ad (patch)
tree10adb053f5130ab83a736db6f1f2f6b54560e215 /kernel
parentsched: Fix load balancing performance regression in should_we_balance() (diff)
sched/fair: Fix small race where child->se.parent,cfs_rq might point to invalid ones
There is a small race between copy_process() and cgroup_attach_task() where child->se.parent,cfs_rq points to invalid (old) ones. parent doing fork() | someone moving the parent to another cgroup -------------------------------+--------------------------------------------- copy_process() + dup_task_struct() -> parent->se is copied to child->se. se.parent,cfs_rq of them point to old ones. cgroup_attach_task() + cgroup_task_migrate() -> parent->cgroup is updated. + cpu_cgroup_attach() + sched_move_task() + task_move_group_fair() +- set_task_rq() -> se.parent,cfs_rq of parent are updated. + cgroup_fork() -> parent->cgroup is copied to child->cgroup. (*1) + sched_fork() + task_fork_fair() -> se.parent,cfs_rq of child are accessed while they point to old ones. (*2) In the worst case, this bug can lead to "use-after-free" and cause a panic, because it's new cgroup's refcount that is incremented at (*1), so the old cgroup(and related data) can be freed before (*2). In fact, a panic caused by this bug was originally caught in RHEL6.4. BUG: unable to handle kernel NULL pointer dereference at (null) IP: [<ffffffff81051e3e>] sched_slice+0x6e/0xa0 [...] Call Trace: [<ffffffff81051f25>] place_entity+0x75/0xa0 [<ffffffff81056a3a>] task_fork_fair+0xaa/0x160 [<ffffffff81063c0b>] sched_fork+0x6b/0x140 [<ffffffff8106c3c2>] copy_process+0x5b2/0x1450 [<ffffffff81063b49>] ? wake_up_new_task+0xd9/0x130 [<ffffffff8106d2f4>] do_fork+0x94/0x460 [<ffffffff81072a9e>] ? sys_wait4+0xae/0x100 [<ffffffff81009598>] sys_clone+0x28/0x30 [<ffffffff8100b393>] stub_clone+0x13/0x20 [<ffffffff8100b072>] ? system_call_fastpath+0x16/0x1b Signed-off-by: Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp> Signed-off-by: Peter Zijlstra <peterz@infradead.org> Cc: <stable@vger.kernel.org> Link: http://lkml.kernel.org/r/039601ceae06$733d3130$59b79390$@mxp.nes.nec.co.jp Signed-off-by: Ingo Molnar <mingo@kernel.org>
Diffstat (limited to 'kernel')
1 files changed, 9 insertions, 5 deletions
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 9b3fe1cd8f40..11cd13667359 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -5928,11 +5928,15 @@ static void task_fork_fair(struct task_struct *p)
cfs_rq = task_cfs_rq(current);
curr = cfs_rq->curr;
- if (unlikely(task_cpu(p) != this_cpu)) {
- rcu_read_lock();
- __set_task_cpu(p, this_cpu);
- rcu_read_unlock();
- }
+ /*
+ * Not only the cpu but also the task_group of the parent might have
+ * been changed after parent->se.parent,cfs_rq were copied to
+ * child->se.parent,cfs_rq. So call __set_task_cpu() to make those
+ * of child point to valid ones.
+ */
+ rcu_read_lock();
+ __set_task_cpu(p, this_cpu);
+ rcu_read_unlock();