linux-kernel - Re: WARNING: at arch/x86/kernel/kvmclock.c:127

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Message-ID: <CA+icZUUcn5-LMxa7rNe7gPSpgnkfb3KX778fR=4UeZuFPYByrw@mail.gmail.com>
Date:	Sun, 10 Jun 2012 18:08:34 +0200
From:	Sedat Dilek <sedat.dilek@...glemail.com>
To:	Eric B Munson <emunson@...bm.net>
Cc:	kvm@...r.kernel.org, LKML <linux-kernel@...r.kernel.org>,
	Avi Kivity <avi@...hat.com>,
	Marcelo Tosatti <mtosatti@...hat.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...e.hu>, x86@...nel.org,
	"Rafael J. Wysocki" <rjw@...k.pl>
Subject: Re: WARNING: at arch/x86/kernel/kvmclock.c:127

On Sun, Jun 10, 2012 at 5:47 PM, Sedat Dilek <sedat.dilek@...glemail.com> wrote:
> Hi,
>
> I see the same warning especially when resuming from a suspend (see
> timestamps >=30-35sec) between Linux v3.5-rc1..v3.5-rc2.
>
> $ sudo grep kvmclock.c /var/log/kern.log
> Jun  4 21:11:32 fambox kernel: [  784.037237] WARNING: at
> arch/x86/kernel/kvmclock.c:127
> kvm_check_and_clear_guest_paused+0x52/0x60()
> Jun  5 20:35:57 fambox kernel: [ 1928.458060] WARNING: at
> arch/x86/kernel/kvmclock.c:127
> kvm_check_and_clear_guest_paused+0x52/0x60()
> Jun  8 09:35:52 fambox kernel: [ 3290.134637] WARNING: at
> arch/x86/kernel/kvmclock.c:127
> kvm_check_and_clear_guest_paused+0x52/0x60()
> Jun  8 09:35:52 fambox kernel: [ 3290.238592] WARNING: at
> arch/x86/kernel/kvmclock.c:127
> kvm_check_and_clear_guest_paused+0x52/0x60()
> Jun  8 12:11:20 fambox kernel: [ 5777.023571] WARNING: at
> arch/x86/kernel/kvmclock.c:127
> kvm_check_and_clear_guest_paused+0x52/0x60()
> Jun  9 13:32:50 fambox kernel: [ 2778.842695] WARNING: at
> arch/x86/kernel/kvmclock.c:127
> kvm_check_and_clear_guest_paused+0x52/0x60()
>
> From [1]:
>
> "...The warning itself is not required for the check_and_clear
> function and can be removed as far as I am concerned."
>
> From [2] commit 3b5d56b9317fa7b5407dff1aa7b115bf6cdbd494 ("kvmclock:
> Add functions to check if the host has stopped the vm")
> ...
> +bool kvm_check_and_clear_guest_paused(void)
> +{
> +       bool ret = false;
> +       struct pvclock_vcpu_time_info *src;
> +
> +       /*
> +        * per_cpu() is safe here because this function is only called from
> +        * timer functions where preemption is already disabled.
> +        */
> +       WARN_ON(!in_atomic());
> +       src = &__get_cpu_var(hv_clock);
> +       if ((src->flags & PVCLOCK_GUEST_STOPPED) != 0) {
> +               __this_cpu_and(hv_clock.flags, ~PVCLOCK_GUEST_STOPPED);
> +               ret = true;
> +       }
> +
> +       return ret;
> +}
> +EXPORT_SYMBOL_GPL(kvm_check_and_clear_guest_paused);
> +
> ...
> ( The export macro was dropped in a followup commit. )
>
> So you mean "WARN_ON(!in_atomic());" can be deleted?
>
> Regards,
> - Sedat -
>
> [1] http://www.spinics.net/lists/kvm/msg73732.html
> [2] http://git.kernel.org/?p=linux/kernel/git/torvalds/linux.git;a=blobdiff;f=arch/x86/kernel/kvmclock.c;h=4ba090ca689db5322fb242b98b53158de5447dc9;hp=f8492da65bfcb03e2775638ad5ce9502099d62c8;hb=3b5d56b9317fa7b5407dff1aa7b115bf6cdbd494;hpb=eae3ee7d8a7c59cf63441dedf28674889f5fc477

[ Removed Glauber Costa - Email-address @ RH does not exist anymore ]
[ Added CC to Rafael  J. Wysocki (S/R) ]

I added for the sake of correctness the last call-trace I have seen
with Linux v3.5-rc2.
And... I had loaded kvm and kvm_intel kernel-modules, but no KVM
instance actively running or active while doing suspend/resume (S/R).

- Sedat -

View attachment "CALL-TRACE_kvmclock_kern-log.txt" of type "text/plain" (9731 bytes)