Re: [PATCH v4 10/19] sched: Fix migrate_disable() vs set_cpus_allowed_ptr()
From: Qian Cai
Date: Thu Nov 12 2020 - 13:01:31 EST
On Thu, 2020-11-12 at 17:26 +0000, Valentin Schneider wrote:
> On 12/11/20 16:38, Qian Cai wrote:
> > Some syscall fuzzing from an unprivileged user starts to trigger this below
> > since this commit first appeared in the linux-next today. Does it ring any
> > bells?
> >
>
> What's the .config? I'm interested in
> CONFIG_PREEMPT
> CONFIG_PREEMPT_RT
> CONFIG_SMP
https://cailca.coding.net/public/linux/mm/git/files/master/arm64.config
# CONFIG_PREEMPT is not set
CONFIG_SMP=y
Also, I have been able to reproduce this on powerpc as well just now.
>
> From a quick look it seems that tree doesn't have Thomas' "generalization" of
> migrate_disable(), so if this doesn't have PREEMPT_RT we could forget about
> migrate_disable() for now.
>
> > [12065.065837][ T1310] INFO: task trinity-c30:91730 blocked for more than
> > 368 seconds.
> > [12065.073524][ T1310] Tainted: G L 5.10.0-rc3-next-
> > 20201112 #2
> > [12065.081076][ T1310] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs"
> > disables this message.
> > [12065.089648][ T1310] task:trinity-c30 state:D stack:26576 pid:91730
> > ppid: 82688 flags:0x00000000
> > [12065.098818][ T1310] Call trace:
> > [12065.101987][ T1310] __switch_to+0xf0/0x1a8
> > [12065.106227][ T1310] __schedule+0x6ec/0x1708
> > [12065.110505][ T1310] schedule+0x1bc/0x3b0
> > [12065.114562][ T1310] schedule_timeout+0x3c4/0x4c0
> > [12065.119275][ T1310] wait_for_completion+0x13c/0x248
> > [12065.124257][ T1310] affine_move_task+0x410/0x688
> > (inlined by) affine_move_task at kernel/sched/core.c:2261
> > [12065.129013][ T1310] __set_cpus_allowed_ptr+0x1b4/0x370
> > [12065.134248][ T1310] sched_setaffinity+0x4f0/0x7e8
> > [12065.139088][ T1310] __arm64_sys_sched_setaffinity+0x1f4/0x2a0
> > [12065.144972][ T1310] do_el0_svc+0x124/0x228
> > [12065.149165][ T1310] el0_sync_handler+0x208/0x384
> > [12065.153876][ T1310] el0_sync+0x140/0x180
> > [12065.157971][ T1310]
>
> So that's a task changing the affinity of some task (either itself or
> another; I can't say without a decoded stacktrace), and then blocking on a
> wait_for_completion() that apparently never happens.
>
> I don't see stop_one_cpu() in the trace, so I assume it's the !task_running
> case, for which the completion should be completed before getting to the
> wait (unless we *do* have migrate_disable()).
>
> Could you please run scripts/decode_stacktrace.sh on the above?
[12065.101987][ T1310] __switch_to (arch/arm64/kernel/process.c:580)
[12065.106227][ T1310] __schedule (kernel/sched/core.c:4272 kernel/sched/core.c:5019)
[12065.110505][ T1310] schedule (./arch/arm64/include/asm/current.h:19 (discriminator 1) ./arch/arm64/include/asm/preempt.h:53 (discriminator 1) kernel/sched/core.c:5099 (discriminator 1))
[12065.114562][ T1310] schedule_timeout (kernel/time/timer.c:1848)
[12065.119275][ T1310] wait_for_completion (kernel/sched/completion.c:85 kernel/sched/completion.c:106 kernel/sched/completion.c:117 kernel/sched/completion.c:138)
[12065.124257][ T1310] affine_move_task (./include/linux/instrumented.h:101 ./include/asm-generic/atomic-instrumented.h:220 ./include/linux/refcount.h:272 ./include/linux/refcount.h:315 ./include/linux/refcount.h:333 kernel/sched/core.c:2263)
[12065.129013][ T1310] __set_cpus_allowed_ptr (kernel/sched/core.c:2353)
[12065.134248][ T1310] sched_setaffinity (kernel/sched/core.c:6460)
[12065.139088][ T1310] __arm64_sys_sched_setaffinity (kernel/sched/core.c:6511 kernel/sched/core.c:6500 kernel/sched/core.c:6500)
[12065.144972][ T1310] do_el0_svc (arch/arm64/kernel/syscall.c:36 arch/arm64/kernel/syscall.c:48 arch/arm64/kernel/syscall.c:159 arch/arm64/kernel/syscall.c:205)
[12065.149165][ T1310] el0_sync_handler (arch/arm64/kernel/entry-common.c:236 arch/arm64/kernel/entry-common.c:254)
[12065.153876][ T1310] el0_sync (arch/arm64/kernel/entry.S:741)
== powerpc ==
[18060.020301][ T676] [c000200014227670] [c000000000a6d1e8] __func__.5350+0x1220e0/0x181338 unreliable
[18060.020333][ T676] [c000200014227850] [c00000000001a278] __switch_to (arch/powerpc/kernel/process.c:1273)
[18060.020351][ T676] [c0002000142278c0] [c0000000008f3e94] __schedule (kernel/sched/core.c:4269 kernel/sched/core.c:5019)
[18060.020377][ T676] [c000200014227990] [c0000000008f4638] schedule (./include/asm-generic/preempt.h:59 (discriminator 1) kernel/sched/core.c:5099 (discriminator 1))
[18060.020394][ T676] [c0002000142279c0] [c0000000008fbd34] schedule_timeout (kernel/time/timer.c:1847)
[18060.020420][ T676] [c000200014227ac0] [c0000000008f6398] wait_for_completion (kernel/sched/completion.c:85 kernel/sched/completion.c:106 kernel/sched/completion.c:117 kernel/sched/completion.c:138)
[18060.020455][ T676] [c000200014227b30] [c000000000100fd4] affine_move_task (kernel/sched/core.c:2261)
[18060.020481][ T676] [c000200014227c90] [c000000000101444] __set_cpus_allowed_ptr (kernel/sched/core.c:2353)
[18060.020507][ T676] [c000200014227d00] [c000000000106eac] sched_setaffinity (kernel/sched/core.c:6460)
[18060.020533][ T676] [c000200014227d70] [c000000000107134] sys_sched_setaffinity (kernel/sched/core.c:6511 kernel/sched/core.c:6500)
[18060.020559][ T676] [c000200014227dc0] [c00000000002a6d8] system_call_exception (arch/powerpc/kernel/syscall_64.c:111)
[18060.020585][ T676] [c000200014227e20] [c00000000000d0a8] system_call_common (arch/powerpc/kernel/entry_64.S:302)