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authorIngo Molnar <mingo@kernel.org>2016-09-15 08:24:53 +0200
committerIngo Molnar <mingo@kernel.org>2016-09-15 08:24:53 +0200
commitd4b80afbba49e968623330f1336da8c724da8aad (patch)
treea9478bd77d8b001a6a7119328d34e9666d7bfe93 /kernel/sched/core.c
parentfcd709ef20a9d83bdb7524d27cd6719dac8690a0 (diff)
parent4cea8776571b18db7485930cb422faa739580c8c (diff)
Merge branch 'linus' into x86/asm, to pick up recent fixes
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Diffstat (limited to 'kernel/sched/core.c')
-rw-r--r--kernel/sched/core.c22
1 files changed, 22 insertions, 0 deletions
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 3d91b63dd2f6..0b6238f18da2 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -2016,6 +2016,28 @@ try_to_wake_up(struct task_struct *p, unsigned int state, int wake_flags)
success = 1; /* we're going to change ->state */
cpu = task_cpu(p);
+ /*
+ * Ensure we load p->on_rq _after_ p->state, otherwise it would
+ * be possible to, falsely, observe p->on_rq == 0 and get stuck
+ * in smp_cond_load_acquire() below.
+ *
+ * sched_ttwu_pending() try_to_wake_up()
+ * [S] p->on_rq = 1; [L] P->state
+ * UNLOCK rq->lock -----.
+ * \
+ * +--- RMB
+ * schedule() /
+ * LOCK rq->lock -----'
+ * UNLOCK rq->lock
+ *
+ * [task p]
+ * [S] p->state = UNINTERRUPTIBLE [L] p->on_rq
+ *
+ * Pairs with the UNLOCK+LOCK on rq->lock from the
+ * last wakeup of our task and the schedule that got our task
+ * current.
+ */
+ smp_rmb();
if (p->on_rq && ttwu_remote(p, wake_flags))
goto stat;