Re: [PATCH] tests/avocado/reverse_debugging: Disable the ppc64 tests by default

[Ani Sinha]

> On 15-Nov-2023, at 10:52 PM, Daniel P. Berrangé <berrange@redhat.com> wrote:
> 
> On Wed, Nov 15, 2023 at 01:14:53PM +0000, Daniel P. Berrangé wrote:
>> On Wed, Nov 15, 2023 at 07:23:01AM +0100, Thomas Huth wrote:
>>> On 15/11/2023 02.15, Nicholas Piggin wrote:
>>>> On Wed Nov 15, 2023 at 4:29 AM AEST, Thomas Huth wrote:
>>>>> On 14/11/2023 17.37, Philippe Mathieu-Daudé wrote:
>>>>>> On 14/11/23 17:31, Thomas Huth wrote:
>>>>>>> The tests seem currently to be broken. Disable them by default
>>>>>>> until someone fixes them.
>>>>>>> 
>>>>>>> Signed-off-by: Thomas Huth <thuth@redhat.com>
>>>>>>> ---
>>>>>>>   tests/avocado/reverse_debugging.py | 7 ++++---
>>>>>>>   1 file changed, 4 insertions(+), 3 deletions(-)
>>>>>> 
>>>>>> Similarly, I suspect https://gitlab.com/qemu-project/qemu/-/issues/1961
>>>>>> which has a fix ready:
>>>>>> https://lore.kernel.org/qemu-devel/20231110170831.185001-1-richard.henderson@linaro.org/
>>>>>> 
>>>>>> Maybe wait the fix gets in first?
>>>>> 
>>>>> No, I applied Richard's patch, but the problem persists. Does this test
>>>>> still work for you?
>>>> 
>>>> I bisected it to 1d4796cd008373 ("python/machine: use socketpair() for
>>>> console connections"),
>>> 
>>> Maybe John (who wrote that commit) can help?
>> 
>> I find it hard to believe this commit is a direct root cause of the
>> problem since all it does is change the QEMU startup sequence so that
>> instead of QEMU listening for a monitor connection, it is given a
>> pre-opened monitor connection.
>> 
>> At the very most that should affect the startup timing a little.
>> 
>> I notice all the reverse debugging tests have a skip on gitlab
>> with a comment:
>> 
>>    # unidentified gitlab timeout problem
>> 
>> this makes be suspicious that John's patch has merely made this
>> (henceforth undiagnosed) timeout more likely to ocurr.
> 
> After an absolutely horrendous hours long debugging session I think
> I figured out the problem. The QEMU process is blocking in
> 
>    qemu_chr_write_buffer
> 
> spinning in the loop on EAGAIN.
> 
> The Python  Machine() class has passed one of a pre-created socketpair
> FDs for the serial port chardev. The guest is trying to write to this
> and blocking.  Nothing in the Machine() class is reading from the
> other end of the serial port console.
> 
> 
> Before John's change, the serial port uses a chardev in server mode
> and crucially  'wait=off', and the Machine() class never opened the
> console socket unless the test case wanted to read from it.
> 
> IOW, QEMU had a background job setting there waiting for a connection
> that would never come.
> 
> As a result when QEMU started executing the guest, all the serial port
> writes get sent into to the void.
> 
> 
> So John's patch has had a semantic change in behaviour, because the
> console socket is permanently open, and thus socket buffers are liable
> to fill up.
> 
> As a demo I increased the socket buffers to 1MB and everything then
> succeeded.
> 
> @@ -357,6 +360,10 @@ def _pre_launch(self) -> None:
> 
>         if self._console_set:
>             self._cons_sock_pair = socket.socketpair()
> +            self._cons_sock_pair[0].setsockopt(socket.SOL_SOCKET, 
> socket.SO_SNDBUF, 1024*1024);
> +            self._cons_sock_pair[0].setsockopt(socket.SOL_SOCKET, 
> socket.SO_RCVBUF, 1024*1024);
> +            self._cons_sock_pair[1].setsockopt(socket.SOL_SOCKET, 
> socket.SO_SNDBUF, 1024*1024);
> +            self._cons_sock_pair[1].setsockopt(socket.SOL_SOCKET, 
> socket.SO_RCVBUF, 1024*1024);
>             os.set_inheritable(self._cons_sock_pair[0].fileno(), True)
> 
>         # NOTE: Make sure any opened resources are *definitely* freed in
> 
> 
> The Machine class doesn't know if anything will ever use the console,
> so as is the change is unsafe.
> 
> The original goal of John's change was to guarantee we capture early
> boot messages as some test need that.

As in 
https://gitlab.com/qemu-project/qemu/-/blob/master/tests/avocado/acpi-bits.py?ref_type=heads#L395
 ?
Some other tests do this too.

>  
> 
> I think we need to be able to have a flag to say whether the caller needs
> an "early console" facility, and only use the pre-opened FD passing for
> that case. Tests we need early console will have to ask for that guarantee
> explicitly.
> 
> With regards,
> Daniel
> -- 
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