Messages in this thread | | | Date | Sat, 28 Nov 2009 14:12:48 +0200 | From | Avi Kivity <> | Subject | Re: WARNING: kernel/smp.c:292 smp_call_function_single [Was: mmotm 2009-11-24-16-47 uploaded] |
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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@linux-foundation.org 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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