From: Frederic Weisbecker <frederic@kernel.org>
To: Valentin Schneider <valentin.schneider@arm.com>
Cc: Guenter Roeck <linux@roeck-us.net>,
linux-kernel@vger.kernel.org, linux-tip-commits@vger.kernel.org,
Ingo Molnar <mingo@kernel.org>,
Peter Zijlstra <peterz@infradead.org>,
x86@kernel.org
Subject: Re: [tip: sched/core] sched/core: Initialize the idle task with preemption disabled
Date: Wed, 7 Jul 2021 14:03:05 +0200 [thread overview]
Message-ID: <20210707120305.GB115752@lothringen> (raw)
In-Reply-To: <87fswr6lqv.mognet@arm.com>
On Wed, Jul 07, 2021 at 12:55:20AM +0100, 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?
>
> I can't make sense of this right now, but it's a bit late :) I'll grab some
> toolchain+qemu tomorrow and go poke at it (and while at it I need to do the
> same with powerpc).
One possible issue is that s390's init_idle_preempt_count() doesn't apply on the
target idle task but on the _current_ CPU. And since smp_init() ->
idle_threads_init() is actually called remotely, we are overwriting the current
CPU preempt_count() instead of the target one.
next prev parent reply other threads:[~2021-07-07 12:03 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-05-12 9:46 [PATCH] sched: Initialize the idle task with preemption disabled Valentin Schneider
2021-05-12 11:15 ` [tip: sched/core] sched/core: " tip-bot2 for Valentin Schneider
2021-07-06 19:44 ` Guenter Roeck
2021-07-06 23:55 ` Valentin Schneider
2021-07-07 4:06 ` Guenter Roeck
2021-07-07 12:03 ` Frederic Weisbecker [this message]
2021-07-07 12:11 ` Valentin Schneider
2021-07-07 14:14 ` Guenter Roeck
2021-07-07 14:35 ` Alexey Kardashevskiy
2021-07-07 14:57 ` Valentin Schneider
2021-07-07 15:31 ` Guenter Roeck
2021-07-07 16:35 ` Guenter Roeck
2021-07-07 17:31 ` Valentin Schneider
2021-07-08 1:50 ` Alexey Kardashevskiy
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