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authorPeter Zijlstra <peterz@infradead.org>2013-10-10 20:17:22 +0200
committerIngo Molnar <mingo@kernel.org>2013-10-16 14:22:14 +0200
commit746023159c40c523b08a3bc3d213dac212385895 (patch)
tree5ec30b81b256a202bf44940360dd1849325c4af8 /kernel/sched
parent7c3f2ab7b844f1a859afbc3d41925e8a0faba5fa (diff)
sched: Fix race in migrate_swap_stop()
There is a subtle race in migrate_swap, when task P, on CPU A, decides to swap places with task T, on CPU B. Task P: - call migrate_swap Task T: - go to sleep, removing itself from the runqueue Task P: - double lock the runqueues on CPU A & B Task T: - get woken up, place itself on the runqueue of CPU C Task P: - see that task T is on a runqueue, and pretend to remove it from the runqueue on CPU B Now CPUs B & C both have corrupted scheduler data structures. This patch fixes it, by holding the pi_lock for both of the tasks involved in the migrate swap. This prevents task T from waking up, and placing itself onto another runqueue, until after migrate_swap has released all locks. This means that, when migrate_swap checks, task T will be either on the runqueue where it was originally seen, or not on any runqueue at all. Migrate_swap deals correctly with of those cases. Tested-by: Joe Mario <jmario@redhat.com> Acked-by: Mel Gorman <mgorman@suse.de> Reviewed-by: Rik van Riel <riel@redhat.com> Signed-off-by: Peter Zijlstra <peterz@infradead.org> Cc: hannes@cmpxchg.org Cc: aarcange@redhat.com Cc: srikar@linux.vnet.ibm.com Cc: tglx@linutronix.de Cc: hpa@zytor.com Link: http://lkml.kernel.org/r/20131010181722.GO13848@laptop.programming.kicks-ass.net Signed-off-by: Ingo Molnar <mingo@kernel.org>
Diffstat (limited to 'kernel/sched')
-rw-r--r--kernel/sched/core.c4
-rw-r--r--kernel/sched/fair.c9
-rw-r--r--kernel/sched/sched.h18
3 files changed, 22 insertions, 9 deletions
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 0c3feebcf112..a972acd468b0 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -1049,6 +1049,8 @@ static int migrate_swap_stop(void *data)
src_rq = cpu_rq(arg->src_cpu);
dst_rq = cpu_rq(arg->dst_cpu);
+ double_raw_lock(&arg->src_task->pi_lock,
+ &arg->dst_task->pi_lock);
double_rq_lock(src_rq, dst_rq);
if (task_cpu(arg->dst_task) != arg->dst_cpu)
goto unlock;
@@ -1069,6 +1071,8 @@ static int migrate_swap_stop(void *data)
unlock:
double_rq_unlock(src_rq, dst_rq);
+ raw_spin_unlock(&arg->dst_task->pi_lock);
+ raw_spin_unlock(&arg->src_task->pi_lock);
return ret;
}
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 4aa0b10889d0..813dd61a9b43 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -1448,15 +1448,6 @@ static inline void put_numa_group(struct numa_group *grp)
kfree_rcu(grp, rcu);
}
-static void double_lock(spinlock_t *l1, spinlock_t *l2)
-{
- if (l1 > l2)
- swap(l1, l2);
-
- spin_lock(l1);
- spin_lock_nested(l2, SINGLE_DEPTH_NESTING);
-}
-
static void task_numa_group(struct task_struct *p, int cpupid, int flags,
int *priv)
{
diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index d69cb325c27e..ffc708717b70 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -1249,6 +1249,24 @@ static inline void double_unlock_balance(struct rq *this_rq, struct rq *busiest)
lock_set_subclass(&this_rq->lock.dep_map, 0, _RET_IP_);
}
+static inline void double_lock(spinlock_t *l1, spinlock_t *l2)
+{
+ if (l1 > l2)
+ swap(l1, l2);
+
+ spin_lock(l1);
+ spin_lock_nested(l2, SINGLE_DEPTH_NESTING);
+}
+
+static inline void double_raw_lock(raw_spinlock_t *l1, raw_spinlock_t *l2)
+{
+ if (l1 > l2)
+ swap(l1, l2);
+
+ raw_spin_lock(l1);
+ raw_spin_lock_nested(l2, SINGLE_DEPTH_NESTING);
+}
+
/*
* double_rq_lock - safely lock two runqueues
*