Re: [tip:sched/core] sched: Change the sched_class::set_cpus_allowed( ) calling context

[Sasha Levin <sasha.levin@oracle.com>]

On 08/12/2015 08:38 AM, tip-bot for Peter Zijlstra wrote:
> Commit-ID:  6c37067e27867db172b988cc11b9ff921175dee5
> Gitweb:     http://git.kernel.org/tip/6c37067e27867db172b988cc11b9ff921175dee5
> Author:     Peter Zijlstra <peterz@infradead.org>
> AuthorDate: Fri, 15 May 2015 17:43:36 +0200
> Committer:  Ingo Molnar <mingo@kernel.org>
> CommitDate: Wed, 12 Aug 2015 12:06:10 +0200
> 
> sched: Change the sched_class::set_cpus_allowed() calling context
> 
> Change the calling context of sched_class::set_cpus_allowed() such
> that we can assume the task is inactive.
> 
> This allows us to easily make changes that affect accounting done by
> enqueue/dequeue. This does in fact completely remove
> set_cpus_allowed_rt() and greatly reduces set_cpus_allowed_dl().
> 
> 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>
> Cc: dedekind1@gmail.com
> Cc: juri.lelli@arm.com
> Cc: mgorman@suse.de
> Cc: riel@redhat.com
> Cc: rostedt@goodmis.org
> Link: http://lkml.kernel.org/r/20150515154833.667516139@infradead.org
> Signed-off-by: Ingo Molnar <mingo@kernel.org>

Hey Peter,

This patch breaks boot inside my VM:

[79817.224383] bad: scheduling from the idle thread!
[79817.224900] CPU: 0 PID: 1 Comm: swapper/0 Not tainted 4.2.0-rc6-next-20150813-sasha-00040-g059fd6d #2431
[79817.225709]  ffffffffae0c6320 ffff880051b77c00 ffffffffade7f739 ffff8800a69e15c0
[79817.226419]  ffff880051b77c18 ffffffffa43c4ed3 ffff880051be8000 ffff880051b77c48
[79817.227122]  ffffffffa43a7ffb ffff880051be8000 ffff8800a69e15c0 ffffffffae094d40
[79817.227806] Call Trace:
[79817.228039] dump_stack (lib/dump_stack.c:52)
[79817.228503] dequeue_task_idle (kernel/sched/idle_task.c:45)
[79817.229005] dequeue_task (kernel/sched/core.c:839)
[79817.229485] do_set_cpus_allowed (kernel/sched/core.c:1178 (discriminator 9))
[79817.230006] init_idle (kernel/sched/core.c:4937)
[79817.230467] idle_thread_get (kernel/smpboot.c:35)
[79817.230945] ? cpu_up (kernel/cpu.c:569)
[79817.231374] _cpu_up (kernel/cpu.c:513)
[79817.231801] ? cpu_down (kernel/cpu.c:500)
[79817.232254] ? fork_idle (kernel/fork.c:1688)
[79817.232731] ? find_next_bit (lib/find_bit.c:65)
[79817.233216] ? idle_threads_init (include/linux/cpumask.h:189 kernel/smpboot.c:71)
[79817.233715] cpu_up (kernel/cpu.c:574)
[79817.234132] smp_init (kernel/smp.c:578)
[79817.234557] kernel_init_freeable (init/main.c:690 init/main.c:884 init/main.c:1009)
[79817.235095] ? start_kernel (init/main.c:979)
[79817.235575] ? finish_task_switch (kernel/sched/sched.h:1087 kernel/sched/core.c:2526)
[79817.236106] ? rest_init (init/main.c:934)
[79817.236567] kernel_init (init/main.c:939)
[79817.237020] ? rest_init (init/main.c:934)
[79817.237496] ret_from_fork (arch/x86/entry/entry_64.S:473)
[79817.237994] ? rest_init (init/main.c:934)
[79817.238477] BUG: unable to handle kernel NULL pointer dereference at           (null)
[79817.239170] IP: [< (null)>] null)  (??:?)
[79817.239608] PGD 0
[79817.239802] Oops: 0010 [#1] SMP DEBUG_PAGEALLOC KASAN
[79817.240295] Dumping ftrace buffer:
[79817.240593]    (ftrace buffer empty)
[79817.240899] Modules linked in:
[79817.241180] CPU: 0 PID: 1 Comm: swapper/0 Not tainted 4.2.0-rc6-next-20150813-sasha-00040-g059fd6d #2431
[79817.241957] task: ffff880278228000 ti: ffff880051b70000 task.ti: ffff880051b70000
[79817.242573] RIP: [< (null)>] null)  (??:?)
[79817.243203] RSP: 0000:ffff880051b77c18  EFLAGS: 00010046
[79817.243646] RAX: dffffc0000000000 RBX: ffff880051be8000 RCX: 0000000000000004
[79817.244229] RDX: 0000000000000000 RSI: ffff880051be8000 RDI: ffff8800a69e15c0
[79817.244815] RBP: ffff880051b77c48 R08: 0000000000000001 R09: 0000000000000004
[79817.245404] R10: ffffed00ff815e03 R11: ffffed00ff815e01 R12: ffff8800a69e15c0
[79817.245987] R13: ffffffffae0c6320 R14: 0000000000000000 R15: 00004897e6254646
[79817.246577] FS:  0000000000000000(0000) GS:ffff880052600000(0000) knlGS:0000000000000000
[79817.247243] CS:  0010 DS: 0000 ES: 0000 CR0: 000000008005003b
[79817.247723] CR2: 0000000000000000 CR3: 0000000030a2d000 CR4: 00000000000006b0
[79817.248319] Stack:
[79817.248496]  ffffffffa43a7d9b ffff880051be8000 ffff8800a69e15c0 ffffffffae0c6320
[79817.249176]  ffff880051be8058 0000000000000001 ffff880051b77c88 ffffffffa43aab66
[79817.249850]  ffff880051be8000 ffff8800a69e15c0 0000000000000001 0000000000000001
[79817.250521] Call Trace:
[79817.250735] ? enqueue_task (kernel/sched/core.c:832)
[79817.251211] do_set_cpus_allowed (kernel/sched/core.c:1189)
[79817.251720] init_idle (kernel/sched/core.c:4937)
[79817.252153] idle_thread_get (kernel/smpboot.c:35)
[79817.252623] ? cpu_up (kernel/cpu.c:569)
[79817.253045] _cpu_up (kernel/cpu.c:513)
[79817.253471] ? cpu_down (kernel/cpu.c:500)
[79817.253902] ? fork_idle (kernel/fork.c:1688)
[79817.254354] ? find_next_bit (lib/find_bit.c:65)
[79817.254820] ? idle_threads_init (include/linux/cpumask.h:189 kernel/smpboot.c:71)
[79817.255326] cpu_up (kernel/cpu.c:574)
[79817.255729] smp_init (kernel/smp.c:578)
[79817.256158] kernel_init_freeable (init/main.c:690 init/main.c:884 init/main.c:1009)
[79817.256675] ? start_kernel (init/main.c:979)
[79817.257158] ? finish_task_switch (kernel/sched/sched.h:1087 kernel/sched/core.c:2526)
[79817.257677] ? rest_init (init/main.c:934)
[79817.258143] kernel_init (init/main.c:939)
[79817.258604] ? rest_init (init/main.c:934)
[79817.259094] ret_from_fork (arch/x86/entry/entry_64.S:473)
[79817.259558] ? rest_init (init/main.c:934)
[79817.260021] Code: Bad RIP value.

Code starting with the faulting instruction
===========================================
[79817.260342] RIP [< (null)>] null)  (??:?)
[79817.260791]  RSP <ffff880051b77c18>
[79817.261098] CR2: 0000000000000000
[79817.261415] ---[ end trace eddc979a4104e4f3 ]---
[79817.261818] Kernel panic - not syncing: Fatal exception


Thanks,
Sasha