From 746023159c40c523b08a3bc3d213dac212385895 Mon Sep 17 00:00:00 2001 From: Peter Zijlstra Date: Thu, 10 Oct 2013 20:17:22 +0200 Subject: [PATCH] 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 Acked-by: Mel Gorman Reviewed-by: Rik van Riel Signed-off-by: Peter Zijlstra 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 --- kernel/sched/core.c | 4 ++++ kernel/sched/fair.c | 9 --------- kernel/sched/sched.h | 18 ++++++++++++++++++ 3 files changed, 22 insertions(+), 9 deletions(-) diff --git a/kernel/sched/core.c b/kernel/sched/core.c index 0c3feeb..a972acd 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 4aa0b10..813dd61 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 d69cb32..ffc7087 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 * -- 2.7.4