Re: [Qemu-devel] [PATCH] main-loop.c: Handle SIGINT, SIGHUP and SIGTERM synchronously

[Jan Kiszka <jan.kiszka@web.de>]

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On 2014-10-25 13:34, Gonglei wrote:
> Hi,
> 
>> Subject: [Qemu-devel] [PATCH] main-loop.c: Handle SIGINT, SIGHUP and
>> SIGTERM synchronously
>>
>> Add the termination signals SIGINT, SIGHUP and SIGTERM to the
>> list of signals which we handle synchronously via a signalfd.
>> This avoids a race condition where if we took the SIGTERM
>> in the middle of qemu_shutdown_requested:
>>     int r = shutdown_requested;
>> [SIGTERM here...]
>>     shutdown_requested = 0;
>>
>> then the setting of the shutdown_requested flag by
>> termsig_handler() would be lost and QEMU would fail to
>> shut down. This was causing 'make check' to hang occasionally.
>>
>> Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
> 
> I met a really upset thing after this patch, which I can't using gdb debug
> Qemu process well. I use gdb attaching a Qemu process, and press 'c' to continue
> executing. When I want to set a breakpoint for debugging, then press 'ctrl + c',
> the Qemu will exit, because the SIGINT signal is captured by Qemu now. :(
> 
> What's your opinion? Thanks.

Confirmed, you cannot interrupt a running qemu from gdb anymore.

I think this patch has to be reverted and the original issue fixed by
making qemu_shutdown_requested signal-safe. Should be simple, just
convert shutdown_requested into a counter. Need not be atomic, all
happens over the main thread anyway.

Jan


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