1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
|
From b421b140e1845ca99e022f3a17140cc9a6c39e32 Mon Sep 17 00:00:00 2001
From: Oleg Nesterov <oleg@redhat.com>
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 <oleg@redhat.com>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
LKML-Reference: <20100315091014.GA9138@redhat.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com>
---
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
|
