On 04/03/2019 17:31, Julien Grall wrote:
> Hi,
>
> On 04/03/2019 17:06, Marc Zyngier wrote:
>> On 04/03/2019 16:30, Julien Grall wrote:
>>> Hi,
>>>
>>> I noticed some issues with this patch when rebooting a guest after using perf.
>>>
>>> [ 577.513447] BUG: sleeping function called from invalid context at
>>> kernel/locking/mutex.c:908
>>> [ 577.521926] in_atomic(): 1, irqs_disabled(): 0, pid: 2323, name: qemu-system aar
>>> [ 577.529354] 1 lock held by qemu-system-aar/2323:
>>> [ 577.533998] #0: 00000000f4f96804 (&vcpu->mutex){+.+.}, at:
>>> kvm_vcpu_ioctl+0x74/0xac0
>>> [ 577.541865] Preemption disabled at:
>>> [ 577.541871] [<ffff0000100cc82c>] kvm_reset_vcpu+0x1c/0x1d0
>>> [ 577.550882] CPU: 6 PID: 2323 Comm: qemu-system-aar Tainted: G W 5.0.0
>>> #1277
>>> [ 577.559137] Hardware name: AMD Seattle (Rev.B0) Development Board (Overdrive)
>>> (DT)
>>> [ 577.566698] Call trace:
>>> [ 577.569138] dump_backtrace+0x0/0x140
>>> [ 577.572793] show_stack+0x14/0x20
>>> [ 577.576103] dump_stack+0xa0/0xd4
>>> [ 577.579412] ___might_sleep+0x1e4/0x2b0
>>> [ 577.583241] __might_sleep+0x60/0xb8
>>> [ 577.586810] __mutex_lock+0x58/0x860
>>> [ 577.590378] mutex_lock_nested+0x1c/0x28
>>> [ 577.594294] perf_event_ctx_lock_nested+0xf4/0x238
>>> [ 577.599078] perf_event_read_value+0x24/0x60
>>> [ 577.603341] kvm_pmu_get_counter_value+0x80/0xe8
>>> [ 577.607950] kvm_pmu_stop_counter+0x2c/0x98
>>> [ 577.612126] kvm_pmu_vcpu_reset+0x58/0xd0
>>> [ 577.616128] kvm_reset_vcpu+0xec/0x1d0
>>> [ 577.619869] kvm_arch_vcpu_ioctl+0x6b0/0x860
>>> [ 577.624131] kvm_vcpu_ioctl+0xe0/0xac0
>>> [ 577.627876] do_vfs_ioctl+0xbc/0x910
>>> [ 577.631443] ksys_ioctl+0x78/0xa8
>>> [ 577.634751] __arm64_sys_ioctl+0x1c/0x28
>>> [ 577.638667] el0_svc_common+0x90/0x118
>>> [ 577.642408] el0_svc_handler+0x2c/0x80
>>> [ 577.646150] el0_svc+0x8/0xc
>>>
>>> This is happening because the vCPU reset code is now running with preemption
>>> disable. However, the perf code cannot be called with preemption disabled as it
>>> is using mutex.
>>>
>>> Do you have any suggestion on the way to fix this potential issue?
>>
>> Given that the PMU is entirely emulated, it never has any state loaded
>> on the CPU. It thus doesn't need to be part of the non-preemptible section.
>>
>> Can you please give this (untested) patchlet one a go? It's not exactly
>> pretty, but I believe it will do the trick.
>
> It does the trick. Are you going to submit the patch?
Patch? Which patch? ;-)
I'll get around to it at some point after the merge window.
Thanks,
M.
--
Jazz is not dead. It just smells funny...
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