sched/core: Fix update_rq_clock() splat on hotplug (and suspend/resume)

The hotplug code still triggers the warning about using a stale
rq->clock value.

Fix things up to actually run update_rq_clock() in a place where we
record the 'UPDATED' flag, and then modify the annotation to retain
this flag over the rq->lock fiddling that happens as a result of
actually migrating all the tasks elsewhere.

Reported-by: Linus Torvalds <torvalds@linux-foundation.org>
Tested-by: Mike Galbraith <efault@gmx.de>
Tested-by: Sachin Sant <sachinp@linux.vnet.ibm.com>
Tested-by: Borislav Petkov <bp@suse.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Matt Fleming <matt@codeblueprint.co.uk>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Ross Zwisler <zwisler@gmail.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Fixes: 4d25b35ea372 ("sched/fair: Restore previous rq_flags when migrating tasks in hotplug")
Link: http://lkml.kernel.org/r/20170202155506.GX6515@twins.programming.kicks-ass.net
Signed-off-by: Ingo Molnar <mingo@kernel.org>

1 files changed, 4 insertions, 10 deletions

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 34e2291a9a6c..2d6e828a0471 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -5557,7 +5557,7 @@ static void migrate_tasks(struct rq *dead_rq)
 {
         struct rq *rq = dead_rq;
         struct task_struct *next, *stop = rq->stop;
-        struct rq_flags rf, old_rf;
+        struct rq_flags rf;
         int dest_cpu;
 
         /*
@@ -5576,7 +5576,9 @@ static void migrate_tasks(struct rq *dead_rq)
          * class method both need to have an up-to-date
          * value of rq->clock[_task]
          */
+        rq_pin_lock(rq, &rf);
         update_rq_clock(rq);
+        rq_unpin_lock(rq, &rf);
 
         for (;;) {
                 /*
@@ -5589,7 +5591,7 @@ static void migrate_tasks(struct rq *dead_rq)
                 /*
                  * pick_next_task() assumes pinned rq->lock:
                  */
-                rq_pin_lock(rq, &rf);
+                rq_repin_lock(rq, &rf);
                 next = pick_next_task(rq, &fake_task, &rf);
                 BUG_ON(!next);
                 next->sched_class->put_prev_task(rq, next);
@@ -5618,13 +5620,6 @@ static void migrate_tasks(struct rq *dead_rq)
                         continue;
                 }
 
-                /*
-                 * __migrate_task() may return with a different
-                 * rq->lock held and a new cookie in 'rf', but we need
-                 * to preserve rf::clock_update_flags for 'dead_rq'.
-                 */
-                old_rf = rf;
-
                 /* Find suitable destination for @next, with force if needed. */
                 dest_cpu = select_fallback_rq(dead_rq->cpu, next);
 
@@ -5633,7 +5628,6 @@ static void migrate_tasks(struct rq *dead_rq)
                         raw_spin_unlock(&rq->lock);
                         rq = dead_rq;
                         raw_spin_lock(&rq->lock);
-                        rf = old_rf;
                 }
                 raw_spin_unlock(&next->pi_lock);
         }