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[Qemu-devel] Re: [PATCH v3 14/22] kvm: Fix race between timer signals an
From: |
Jan Kiszka |
Subject: |
[Qemu-devel] Re: [PATCH v3 14/22] kvm: Fix race between timer signals and vcpu entry under !IOTHREAD |
Date: |
Mon, 31 Jan 2011 15:31:27 +0100 |
User-agent: |
Mozilla/5.0 (X11; U; Linux i686 (x86_64); de; rv:1.8.1.12) Gecko/20080226 SUSE/2.0.0.12-1.1 Thunderbird/2.0.0.12 Mnenhy/0.7.5.666 |
On 2011-01-31 14:22, Avi Kivity wrote:
> On 01/31/2011 01:27 PM, Jan Kiszka wrote:
>> On 2011-01-31 11:03, Avi Kivity wrote:
>>> On 01/27/2011 04:33 PM, Jan Kiszka wrote:
>>>> Found by Stefan Hajnoczi: There is a race in kvm_cpu_exec between
>>>> checking for exit_request on vcpu entry and timer signals arriving
>>>> before KVM starts to catch them. Plug it by blocking both timer related
>>>> signals also on !CONFIG_IOTHREAD and process those via signalfd.
>>>>
>>>> As this fix depends on real signalfd support (otherwise the timer
>>>> signals only kick the compat helper thread, and the main thread hangs),
>>>> we need to detect the invalid constellation and abort configure.
>>>>
>>>> Signed-off-by: Jan Kiszka<address@hidden>
>>>> CC: Stefan Hajnoczi<address@hidden>
>>>> ---
>>>>
>>>> I don't want to invest that much into !IOTHREAD anymore, so let's see if
>>>> the proposed catch&abort is acceptable.
>>>>
>>>
>>> I don't understand the dependency on signalfd. The normal way of doing
>>> things, either waiting for the signal in sigtimedwait() or in
>>> ioctl(KVM_RUN), works with SIGALRM just fine.
>>
>> And how would you be kicked out of the select() call if it is waiting
>> with a timeout? We only have a single thread here.
>
> If we use signalfd() (either kernel provided or thread+pipe), we kick
> out of select by select()ing it (though I don't see how it works without
> an iothread, since an fd can't stop a vcpu unless you enable SIGIO on
> it, which is silly for signalfd)
>
> If you leave it as a naked signal, then it can break out of either
> pselect() or vcpu.
>
> Since the goal is to drop !CONFIG_IOTHREAD, the first path seems better,
> I just don't understand the problem with emulated signalfd().
>
With the emulated signalfd, there won't be any signal for the VCPU while
in KVM_RUN.
Jan
--
Siemens AG, Corporate Technology, CT T DE IT 1
Corporate Competence Center Embedded Linux
- [Qemu-devel] [PATCH 18/22] kvm: Unconditionally reenter kernel after IO exits, (continued)
- [Qemu-devel] [PATCH 18/22] kvm: Unconditionally reenter kernel after IO exits, Jan Kiszka, 2011/01/27
- [Qemu-devel] [PATCH 14/22] kvm: Fix race between timer signals and vcpu entry under !IOTHREAD, Jan Kiszka, 2011/01/27
- [Qemu-devel] [PATCH v2 14/22] kvm: Fix race between timer signals and vcpu entry under !IOTHREAD, Jan Kiszka, 2011/01/27
- [Qemu-devel] [PATCH v3 14/22] kvm: Fix race between timer signals and vcpu entry under !IOTHREAD, Jan Kiszka, 2011/01/27
- [Qemu-devel] Re: [PATCH v3 14/22] kvm: Fix race between timer signals and vcpu entry under !IOTHREAD, Avi Kivity, 2011/01/31
- [Qemu-devel] Re: [PATCH v3 14/22] kvm: Fix race between timer signals and vcpu entry under !IOTHREAD, Jan Kiszka, 2011/01/31
- Re: [Qemu-devel] Re: [PATCH v3 14/22] kvm: Fix race between timer signals and vcpu entry under !IOTHREAD, Stefan Hajnoczi, 2011/01/31
- Re: [Qemu-devel] Re: [PATCH v3 14/22] kvm: Fix race between timer signals and vcpu entry under !IOTHREAD, Jan Kiszka, 2011/01/31
- Re: [Qemu-devel] Re: [PATCH v3 14/22] kvm: Fix race between timer signals and vcpu entry under !IOTHREAD, Stefan Hajnoczi, 2011/01/31
- [Qemu-devel] Re: [PATCH v3 14/22] kvm: Fix race between timer signals and vcpu entry under !IOTHREAD, Avi Kivity, 2011/01/31
- [Qemu-devel] Re: [PATCH v3 14/22] kvm: Fix race between timer signals and vcpu entry under !IOTHREAD,
Jan Kiszka <=
- [Qemu-devel] Re: [PATCH v3 14/22] kvm: Fix race between timer signals and vcpu entry under !IOTHREAD, Avi Kivity, 2011/01/31
[Qemu-devel] [PATCH 04/22] Leave inner main_loop faster on pending requests, Jan Kiszka, 2011/01/27
[Qemu-devel] [PATCH 11/22] kvm: Refactor qemu_kvm_eat_signals, Jan Kiszka, 2011/01/27
[Qemu-devel] [PATCH 19/22] kvm: Remove static return code of kvm_handle_io, Jan Kiszka, 2011/01/27
[Qemu-devel] [PATCH 05/22] kvm: Report proper error on GET_VCPU_MMAP_SIZE failures, Jan Kiszka, 2011/01/27
[Qemu-devel] [PATCH 06/22] kvm: Drop redundant kvm_enabled from kvm_cpu_thread_fn, Jan Kiszka, 2011/01/27