From b421b140e1845ca99e022f3a17140cc9a6c39e32 Mon Sep 17 00:00:00 2001 From: Oleg Nesterov Date: Mon, 15 Mar 2010 10:10:14 +0100 Subject: [PATCH] sched: move_task_off_dead_cpu(): Remove retry logic commit 2d5a7c7241f20ee8e90452a47b773cffbb4c2412 in tip. The previous patch preserved the retry logic, but it looks unneeded. __migrate_task() can only fail if we raced with migration after we dropped the lock, but in this case the caller of set_cpus_allowed/etc must initiate migration itself if ->on_rq == T. We already fixed p->cpus_allowed, the changes in active/online masks must be visible to racer, it should migrate the task to online cpu correctly. [ upstream commit: c1804d547dc098363443667609c272d1e4d15ee8 ] [PG: warning; this differs from upstream by the critical change: - needs_cpu = (task_cpu(p) == dead_cpu) && (p->state != TASK_WAKING); + needs_cpu = (task_cpu(p) == dead_cpu) && !(p->state & TASK_WAKING); which makes a big difference when on RT, TASK_WAKING is not exclusive.] Signed-off-by: Oleg Nesterov Signed-off-by: Peter Zijlstra LKML-Reference: <20100315091014.GA9138@redhat.com> Signed-off-by: Ingo Molnar Signed-off-by: Thomas Gleixner Signed-off-by: Paul Gortmaker --- kernel/sched.c | 13 ++++++------- 1 files changed, 6 insertions(+), 7 deletions(-) diff --git a/kernel/sched.c b/kernel/sched.c index b52b84d..b973944 100644 --- a/kernel/sched.c +++ b/kernel/sched.c @@ -5892,7 +5892,7 @@ static void move_task_off_dead_cpu(int dead_cpu, struct task_struct *p) struct rq *rq = cpu_rq(dead_cpu); int needs_cpu, uninitialized_var(dest_cpu); unsigned long flags; -again: + local_irq_save(flags); raw_spin_lock(&rq->lock); @@ -5900,14 +5900,13 @@ again: if (needs_cpu) dest_cpu = select_fallback_rq(dead_cpu, p); raw_spin_unlock(&rq->lock); - - /* It can have affinity changed while we were choosing. */ + /* + * It can only fail if we race with set_cpus_allowed(), + * in the racer should migrate the task anyway. + */ if (needs_cpu) - needs_cpu = !__migrate_task(p, dead_cpu, dest_cpu); + __migrate_task(p, dead_cpu, dest_cpu); local_irq_restore(flags); - - if (unlikely(needs_cpu)) - goto again; } /* -- 1.7.0.4