[tip:sched/core] sched: move_task_off_dead_cpu(): Remove retry logic

From: tip-bot for Oleg Nesterov
Date: Fri Apr 02 2010 - 15:12:50 EST

Commit-ID: c1804d547dc098363443667609c272d1e4d15ee8
Gitweb: http://git.kernel.org/tip/c1804d547dc098363443667609c272d1e4d15ee8
Author: Oleg Nesterov <oleg@xxxxxxxxxx>
AuthorDate: Mon, 15 Mar 2010 10:10:14 +0100
Committer: Ingo Molnar <mingo@xxxxxxx>
CommitDate: Fri, 2 Apr 2010 20:12:02 +0200

sched: move_task_off_dead_cpu(): Remove retry logic

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.

Signed-off-by: Oleg Nesterov <oleg@xxxxxxxxxx>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@xxxxxxxxx>
LKML-Reference: <20100315091014.GA9138@xxxxxxxxxx>
Signed-off-by: Ingo Molnar <mingo@xxxxxxx>
kernel/sched.c | 13 ++++++-------
1 files changed, 6 insertions(+), 7 deletions(-)

diff --git a/kernel/sched.c b/kernel/sched.c
index 27774b5..f475c60 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -5456,7 +5456,7 @@ 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;

@@ -5464,14 +5464,13 @@ again:
if (needs_cpu)
dest_cpu = select_fallback_rq(dead_cpu, p);
- /* 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);
- if (unlikely(needs_cpu))
- goto again;

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