On Mon, 11 Jun 2012 19:07:19 -0300, Marcelo Tosatti wrote:
On Mon, Jun 11, 2012 at 05:47:00PM -0400, Eric B Munson wrote:
On Sun, 10 Jun 2012 17:47:24 +0200, Sedat Dilek 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?
Yes.
When I wrote the patch originally, I was under the (incorrect)
assumption that the watch dog was only ever reset in an atomic
context. Given that this is not the case, the warning can be
removed. Though before that happens, I have a question: if this is
called outside of an atomic context, is the use of __get_cpu_Var()
and __this_cpu_and() invalid?
It remains valid because its called with interrupts
disabled (see migrate_hrtimers).
Thank you, that was my assumption but I wanted to confirm. I do not
have access to my working kernel tree and won't for 2 days. I can't get
to the patch until late Wednesday so if someone else wants to work that
up I'd appreciate it.
Thanks,
Eric
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