Re: [PATCH] fuzz: Disable QEMU's signal handlers

[Darren Kenny]

On Tuesday, 2020-10-13 at 17:52:46 +01, Daniel P. Berrangé wrote:
> On Tue, Oct 13, 2020 at 05:50:37PM +0100, Darren Kenny wrote:
>> Hi Alex,
>> 
>> This mentions the use of atexit() to perform some cleanup, but I'm not
>> seeing that being added here, should it be?
>
> The reference to atexit is strange, because it says the only way to
> kill the fuzzer is SIGKILL, and that won't let atexit handlers run
> anyway.
>

OK, I understand the context now, it is in reference to Dima's patchset:

- 
cover.1602078083.git.dimastep@yandex-team.ru/">https://lore.kernel.org/qemu-devel/cover.1602078083.git.dimastep@yandex-team.ru/

Where Alex suggested using atexit() to clean up the left over files from
the test.

And with regard to SIGKILL, I believe it is that today, before Alex's
patch that is the only way to stop the fuzzer running - which I can
attest to since I've found it hard to stop in the past :)

Resetting these signal handlers to the default behaviour would allow the
process to be terminated and an atexit() used, as Alex mentioned.

Alex, if you could clarify the commit message, then I feel this does
make sent to change in the fuzz testing code, so:

Reviewed-by: Darren Kenny <darren.kenny@oracle.com>

Thanks,

Darren.

>> 
>> Thanks,
>> 
>> Darren.
>> 
>> On Tuesday, 2020-10-13 at 11:29:20 -04, Alexander Bulekov wrote:
>> > With the fuzzer, we never call main_loop_should_exit, since we manually
>> > call main_loop_wait. This means that the only way to terminate the
>> > fuzzer is with SIGKILL. Disable the signal handlers, so there are
>> > reasonable ways to terminate the fuzzer and use atexit() to clean-up
>> > after the fuzzer.
>> >
>> > Signed-off-by: Alexander Bulekov <alxndr@bu.edu>
>> > ---
>> >  tests/qtest/fuzz/fuzz.c | 8 ++++++++
>> >  1 file changed, 8 insertions(+)
>> >
>> > diff --git a/tests/qtest/fuzz/fuzz.c b/tests/qtest/fuzz/fuzz.c
>> > index d926c490c5..eb0070437f 100644
>> > --- a/tests/qtest/fuzz/fuzz.c
>> > +++ b/tests/qtest/fuzz/fuzz.c
>> > @@ -217,5 +217,13 @@ int LLVMFuzzerInitialize(int *argc, char ***argv, 
>> > char ***envp)
>> >      /* re-enable the rcu atfork, which was previously disabled in 
>> > qemu_init */
>> >      rcu_enable_atfork();
>> >  
>> > +    /*
>> > +     * Disable QEMU's signal handlers, since we manually control the 
>> > main_loop,
>> > +     * and don't check for main_loop_should_exit
>> > +     */
>> > +    signal(SIGINT, SIG_DFL);
>> > +    signal(SIGHUP, SIG_DFL);
>> > +    signal(SIGTERM, SIG_DFL);
>> > +
>> >      return 0;
>> >  }
>> > -- 
>> > 2.28.0
>> 
>
> Regards,
> Daniel
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