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SubjectRe: [tip: sched/core] sched/core: Initialize the idle task with preemption disabled
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On 7/6/21 4:55 PM, Valentin Schneider wrote:
>
> Hi Guenter,
>
> On 06/07/21 12:44, Guenter Roeck wrote:
>> This patch results in several messages similar to the following
>> when booting s390 images in qemu.
>>
>> [ 1.690807] BUG: sleeping function called from invalid context at include/linux/percpu-rwsem.h:49
>> [ 1.690925] in_atomic(): 1, irqs_disabled(): 0, non_block: 0, pid: 1, name: swapper/0
>> [ 1.691053] no locks held by swapper/0/1.
>> [ 1.691310] CPU: 0 PID: 1 Comm: swapper/0 Not tainted 5.13.0-11788-g79160a603bdb #1
>> [ 1.691469] Hardware name: QEMU 2964 QEMU (KVM/Linux)
>> [ 1.691612] Call Trace:
>> [ 1.691718] [<0000000000d98bb0>] show_stack+0x90/0xf8
>> [ 1.692040] [<0000000000da894c>] dump_stack_lvl+0x74/0xa8
>> [ 1.692134] [<0000000000187e52>] ___might_sleep+0x15a/0x170
>> [ 1.692228] [<000000000014f588>] cpus_read_lock+0x38/0xc0
>> [ 1.692320] [<0000000000182e8a>] smpboot_register_percpu_thread+0x2a/0x160
>> [ 1.692412] [<00000000014814b8>] cpuhp_threads_init+0x28/0x60
>> [ 1.692505] [<0000000001487a30>] smp_init+0x28/0x90
>> [ 1.692597] [<00000000014779a6>] kernel_init_freeable+0x1f6/0x270
>> [ 1.692689] [<0000000000db7466>] kernel_init+0x2e/0x160
>> [ 1.692779] [<0000000000103618>] __ret_from_fork+0x40/0x58
>> [ 1.692870] [<0000000000dc6e12>] ret_from_fork+0xa/0x30
>>
>> Reverting this patch fixes the problem.
>> Bisect log is attached.
>>
>> Guenter
>>
>
> Thanks for the report.
>
> So somehow the init task ends up with a non-zero preempt_count()? Per
> FORK_PREEMPT_COUNT we should exit __ret_from_fork() with a zero count, are
> you hitting the WARN_ONCE() in finish_task_switch()?
>
> Does CONFIG_DEBUG_PREEMPT=y yield anything interesting?
>

My configuration doesn't have CONFIG_PREEMPT enabled.

Guenter

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