Peter Zijlstra wrote:
So what we need to do is make the whole of select_task_rq_fair()
cpu_online/active_mask aware, or give up and simply punt:
diff --git a/kernel/sched.c b/kernel/sched.c
index 1f2e99d..62df61c 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -2377,6 +2377,9 @@ static int try_to_wake_up(struct task_struct *p, unsigned int state,
task_rq_unlock(rq, &flags);
cpu = p->sched_class->select_task_rq(p, SD_BALANCE_WAKE, wake_flags);
+ if (!cpu_active(cpu))
+ cpu = cpumask_any_and(&p->cpus_allowed, cpu_active_mask);
+
if (cpu != orig_cpu) {
local_irq_save(flags);
rq = cpu_rq(cpu);
Something I think Mike also tried and didn't deadlock for him..
Sachin, Mike, could you try the above snippet and verify if it does
indeed solve your respective issues?
Unfortunately the above patch made things worse. With this patch
the machine failed to boot with following oops
CPU0: Dual-Core AMD Opteron(tm) Processor 2218 stepping 02
BUG: unable to handle kernel NULL pointer dereference at 0000000000000020
IP: [<ffffffff81061f17>] set_task_cpu+0x189/0x1ed
PGD 0
Oops: 0000 [#1] SMP
last sysfs file:
CPU 0
Modules linked in:
Pid: 3, comm: kthreadd Not tainted 2.6.32-rc7-next-20091113 #1 BladeCenter LS21 -[79716AA]-
RIP: 0010:[<ffffffff81061f17>] [<ffffffff81061f17>] set_task_cpu+0x189/0x1ed
RSP: 0018:ffff88012b357dd0 EFLAGS: 00010046
RAX: 0000000000000000 RBX: 0000000000000000 RCX: 0000000000000004
RDX: 0000000000000000 RSI: 0000000000000004 RDI: ffff88012b340000
RBP: ffff88012b357e10 R08: 0000000000000004 R09: ffff88012b3401f8
R10: 00000000000cffa7 R11: 0000000000000000 R12: ffff88012b340000
R13: 000000000c28ccf6 R14: 0000000000000004 R15: ffff880028214cc0
FS: 0000000000000000(0000) GS:ffff880028200000(0000) knlGS:0000000000000000
CS: 0010 DS: 0018 ES: 0018 CR0: 000000008005003b
CR2: 0000000000000020 CR3: 000000000174e000 CR4: 00000000000006f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000400
Process kthreadd (pid: 3, threadinfo ffff88012b356000, task ffff88012b3431c0)
Stack:
ffff880028214d20 0000000000000000 0000000028215640 0000000000000000
<0> ffff88012b340000 0000000000000001 ffff880028214cc0 0000000000000000
<0> ffff88012b357e60 ffffffff81063a75 0000000000000000 0000000000000000
Call Trace:
[<ffffffff81063a75>] try_to_wake_up+0x103/0x31f
[<ffffffff81063c9e>] default_wake_function+0xd/0xf
[<ffffffff810519a7>] __wake_up_common+0x46/0x76
[<ffffffff810648ae>] ? migration_thread+0x0/0x285
[<ffffffff810577c8>] complete+0x38/0x4b
[<ffffffff8108040a>] kthread+0x67/0x85
[<ffffffff810298fa>] child_rip+0xa/0x20
[<ffffffff810803a3>] ? kthread+0x0/0x85
[<ffffffff810298f0>] ? child_rip+0x0/0x20
Code: 00 8b 05 dd d7 df 04 85 c0 74 19 45 31 c0 31 c9 ba 01 00 00 00 be 01 00 00 00 bf 04 00 00 00 e8 79 02 07 00 48 8b 55 c8 44 89 f1 <48> 8b 42 20 48 8b 55 c0 49 03 84 24 88 00 00 00 48 2b 42 20 49
RIP [<ffffffff81061f17>] set_task_cpu+0x189/0x1ed
RSP <ffff88012b357dd0>
CR2: 0000000000000020
---[ end trace 4eaa2a86a8e2da22 ]---
I tried this with today's next (2.6.32-rc7-20091113) + the above patch.
Here is how the code looks after applying the patch...
task_rq_unlock(rq, &flags);
cpu = p->sched_class->select_task_rq(p, SD_BALANCE_WAKE, wake_flags);
if (!cpu_active(cpu))
cpu = cpumask_any_and(&p->cpus_allowed, cpu_active_mask);
if (cpu != orig_cpu)
set_task_cpu(p, cpu);
Thanks
-Sachin
--
---------------------------------
Sachin Sant
IBM Linux Technology Center
India Systems and Technology Labs
Bangalore, India
---------------------------------
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