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authorPeter Zijlstra <a.p.zijlstra@chello.nl>2010-03-24 18:34:10 +0100
committerIngo Molnar <mingo@elte.hu>2010-04-02 20:12:03 +0200
commit0017d735092844118bef006696a750a0e4ef6ebd (patch)
tree8ed1540aaeb63da726f93da12950a8eaa0e0a3e0 /kernel/sched_fair.c
parent9084bb8246ea935b98320554229e2f371f7f52fa (diff)
sched: Fix TASK_WAKING vs fork deadlock
Oleg noticed a few races with the TASK_WAKING usage on fork. - since TASK_WAKING is basically a spinlock, it should be IRQ safe - since we set TASK_WAKING (*) without holding rq->lock it could be there still is a rq->lock holder, thereby not actually providing full serialization. (*) in fact we clear PF_STARTING, which in effect enables TASK_WAKING. Cure the second issue by not setting TASK_WAKING in sched_fork(), but only temporarily in wake_up_new_task() while calling select_task_rq(). Cure the first by holding rq->lock around the select_task_rq() call, this will disable IRQs, this however requires that we push down the rq->lock release into select_task_rq_fair()'s cgroup stuff. Because select_task_rq_fair() still needs to drop the rq->lock we cannot fully get rid of TASK_WAKING. Reported-by: Oleg Nesterov <oleg@redhat.com> Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl> LKML-Reference: <new-submission> Signed-off-by: Ingo Molnar <mingo@elte.hu>
Diffstat (limited to 'kernel/sched_fair.c')
-rw-r--r--kernel/sched_fair.c8
1 files changed, 6 insertions, 2 deletions
diff --git a/kernel/sched_fair.c b/kernel/sched_fair.c
index 49ad99378f82..8a5e7632d09b 100644
--- a/kernel/sched_fair.c
+++ b/kernel/sched_fair.c
@@ -1423,7 +1423,8 @@ select_idle_sibling(struct task_struct *p, struct sched_domain *sd, int target)
*
* preempt must be disabled.
*/
-static int select_task_rq_fair(struct task_struct *p, int sd_flag, int wake_flags)
+static int
+select_task_rq_fair(struct rq *rq, struct task_struct *p, int sd_flag, int wake_flags)
{
struct sched_domain *tmp, *affine_sd = NULL, *sd = NULL;
int cpu = smp_processor_id();
@@ -1521,8 +1522,11 @@ static int select_task_rq_fair(struct task_struct *p, int sd_flag, int wake_flag
cpumask_weight(sched_domain_span(sd))))
tmp = affine_sd;
- if (tmp)
+ if (tmp) {
+ raw_spin_unlock(&rq->lock);
update_shares(tmp);
+ raw_spin_lock(&rq->lock);
+ }
}
#endif