| Message ID | alpine.DEB.2.10.1604151814580.2526@sstabellini-ThinkPad-X260 (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
On 16/04/16 03:23, Stefano Stabellini wrote: > On slow platforms with unreliable TSC, such as QEMU emulated machines, > it is possible for the kernel to request the next event in the past. In > that case, in the current implementation of xen_vcpuop_clockevent, we > simply return -ETIME. To be precise the Xen returns -ETIME and we pass > it on. However the result of this is a missed event, which simply causes > the kernel to hang. > > Instead it is better to always ask the hypervisor for a timer event, > even if the timeout is in the past. That way there are no lost > interrupts and the kernel survives. To do that, remove the > VCPU_SSHOTTMR_future flag. > > Signed-off-by: Stefano Stabellini <sstabellini@kernel.org> Acked-by: Juergen Gross <jgross@suse.com> > > diff --git a/arch/x86/xen/time.c b/arch/x86/xen/time.c > index a0a4e55..6deba5b 100644 > --- a/arch/x86/xen/time.c > +++ b/arch/x86/xen/time.c > @@ -290,11 +290,11 @@ static int xen_vcpuop_set_next_event(unsigned long delta, > WARN_ON(!clockevent_state_oneshot(evt)); > > single.timeout_abs_ns = get_abs_timeout(delta); > - single.flags = VCPU_SSHOTTMR_future; > + /* Get an event anyway, even if the timeout is already expired */ > + single.flags = 0; > > ret = HYPERVISOR_vcpu_op(VCPUOP_set_singleshot_timer, cpu, &single); > - > - BUG_ON(ret != 0 && ret != -ETIME); > + BUG_ON(ret != 0); > > return ret; > } >
On Thu, 21 Apr 2016, Juergen Gross wrote: > On 16/04/16 03:23, Stefano Stabellini wrote: > > On slow platforms with unreliable TSC, such as QEMU emulated machines, > > it is possible for the kernel to request the next event in the past. In > > that case, in the current implementation of xen_vcpuop_clockevent, we > > simply return -ETIME. To be precise the Xen returns -ETIME and we pass > > it on. However the result of this is a missed event, which simply causes > > the kernel to hang. > > > > Instead it is better to always ask the hypervisor for a timer event, > > even if the timeout is in the past. That way there are no lost > > interrupts and the kernel survives. To do that, remove the > > VCPU_SSHOTTMR_future flag. > > > > Signed-off-by: Stefano Stabellini <sstabellini@kernel.org> > > Acked-by: Juergen Gross <jgross@suse.com> I committed it to xentip/for-linus-4.7 > > diff --git a/arch/x86/xen/time.c b/arch/x86/xen/time.c > > index a0a4e55..6deba5b 100644 > > --- a/arch/x86/xen/time.c > > +++ b/arch/x86/xen/time.c > > @@ -290,11 +290,11 @@ static int xen_vcpuop_set_next_event(unsigned long delta, > > WARN_ON(!clockevent_state_oneshot(evt)); > > > > single.timeout_abs_ns = get_abs_timeout(delta); > > - single.flags = VCPU_SSHOTTMR_future; > > + /* Get an event anyway, even if the timeout is already expired */ > > + single.flags = 0; > > > > ret = HYPERVISOR_vcpu_op(VCPUOP_set_singleshot_timer, cpu, &single); > > - > > - BUG_ON(ret != 0 && ret != -ETIME); > > + BUG_ON(ret != 0); > > > > return ret; > > } > > >
diff --git a/arch/x86/xen/time.c b/arch/x86/xen/time.c index a0a4e55..6deba5b 100644 --- a/arch/x86/xen/time.c +++ b/arch/x86/xen/time.c @@ -290,11 +290,11 @@ static int xen_vcpuop_set_next_event(unsigned long delta, WARN_ON(!clockevent_state_oneshot(evt)); single.timeout_abs_ns = get_abs_timeout(delta); - single.flags = VCPU_SSHOTTMR_future; + /* Get an event anyway, even if the timeout is already expired */ + single.flags = 0; ret = HYPERVISOR_vcpu_op(VCPUOP_set_singleshot_timer, cpu, &single); - - BUG_ON(ret != 0 && ret != -ETIME); + BUG_ON(ret != 0); return ret; }
On slow platforms with unreliable TSC, such as QEMU emulated machines, it is possible for the kernel to request the next event in the past. In that case, in the current implementation of xen_vcpuop_clockevent, we simply return -ETIME. To be precise the Xen returns -ETIME and we pass it on. However the result of this is a missed event, which simply causes the kernel to hang. Instead it is better to always ask the hypervisor for a timer event, even if the timeout is in the past. That way there are no lost interrupts and the kernel survives. To do that, remove the VCPU_SSHOTTMR_future flag. Signed-off-by: Stefano Stabellini <sstabellini@kernel.org>