On 11/27/2009 06:37 PM, Thomas Gleixner wrote:
On Fri, 27 Nov 2009, Peter Zijlstra wrote:
On Fri, 2009-11-27 at 16:03 +0100, Jiri Slaby wrote:
On 11/25/2009 01:47 AM, akpm@xxxxxxxxxxxxxxxxxxxx wrote:
The mm-of-the-moment snapshot 2009-11-24-16-47 has been uploaded to
Hi, when executing qemu-kvm I often get following warning and a hard lockup.
WARNING: at kernel/smp.c:292 smp_call_function_single+0xbd/0x140()
Hardware name: To Be Filled By O.E.M.
Modules linked in: kvm_intel kvm fuse ath5k ath
Pid: 3265, comm: qemu-kvm Not tainted 2.6.32-rc8-mm1_64 #912
Call Trace:
[<ffffffff81039678>] warn_slowpath_common+0x78/0xb0
[<ffffffffa007fd50>] ? __vcpu_clear+0x0/0xd0 [kvm_intel]
[<ffffffff810396bf>] warn_slowpath_null+0xf/0x20
[<ffffffff8106410d>] smp_call_function_single+0xbd/0x140
[<ffffffffa0080af6>] vmx_vcpu_load+0x46/0x170 [kvm_intel]
[<ffffffffa004dd94>] kvm_arch_vcpu_load+0x24/0x60 [kvm]
[<ffffffffa0047a8d>] kvm_sched_in+0xd/0x10 [kvm]
[<ffffffff8102de37>] finish_task_switch+0x67/0xc0
[<ffffffff814699f8>] schedule+0x2f8/0x9c0
It is a regression against 2009-11-13-19-59.
Any ideas?
Looks like kvm is trying to send an IPI from the preempt notifiers,
which are called with IRQs disabled, not a sane thing to do.
If they really want that, they'll have to use a pre-allocated struct
call_single_data and use __smp_call_function_single.
Hmm, commit 498657a moved the fire_sched_in_preempt_notifiers() call
into the irqs disabled section recently.
sched, kvm: Fix race condition involving sched_in_preempt_notifers
In finish_task_switch(), fire_sched_in_preempt_notifiers() is
called after finish_lock_switch().
However, depending on architecture, preemption can be enabled after
finish_lock_switch() which breaks the semantics of preempt
notifiers.
So move it before finish_arch_switch(). This also makes the in-
notifiers symmetric to out- notifiers in terms of locking - now
both are called under rq lock.
It's not a surprise that this breaks the existing code which does the
smp function call.
Yes, kvm expects preempt notifiers to be run with irqs enabled. Copying
patch author.
--
Do not meddle in the internals of kernels, for they are subtle and quick to panic.
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