Commit 4d25b35e authored Oct 26, 2016 by Matt Fleming Committed by Ingo Molnar Jan 30, 2017

sched/fair: Restore previous rq_flags when migrating tasks in hotplug



__migrate_task() can return with a different runqueue locked than the
one we passed as an argument. So that we can repin the lock in
migrate_tasks() (and keep the update_rq_clock() bit) we need to
restore the old rq_flags before repinning.

Note that it wouldn't be correct to change move_queued_task() to repin
because of the change of runqueue and the fact that having an
up-to-date clock on the initial rq doesn't mean the new rq has one
too.

Signed-off-by: Matt Fleming <matt@codeblueprint.co.uk>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Ingo Molnar <mingo@kernel.org>

parent 1b1d6225

kernel/sched/core.c

+9 −1

Original line number	Diff line number	Diff line
		@@ -5608,7 +5608,7 @@ static void migrate_tasks(struct rq *dead_rq)
		{
		struct rq *rq = dead_rq;
		struct task_struct next, stop = rq->stop;
		struct rq_flags rf;
		struct rq_flags rf, old_rf;
		int dest_cpu;

		/*
		@@ -5669,6 +5669,13 @@ 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);

		@@ -5677,6 +5684,7 @@ 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);
		}