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Subject: Re: For review: seccomp_user_notif(2) manual page
To:     Jann Horn <jannh@google.com>
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From:   "Michael Kerrisk (man-pages)" <mtk.manpages@gmail.com>
Message-ID: <e2643168-b5d5-4d8c-947a-7895bcabc268@gmail.com>
Date:   Tue, 27 Oct 2020 07:14:03 +0100
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On 10/26/20 4:54 PM, Jann Horn wrote:
> On Sun, Oct 25, 2020 at 5:32 PM Michael Kerrisk (man-pages)
> <mtk.manpages@gmail.com> wrote:
[...]
>> I tried applying the patch below to vanilla 5.9.0.
>> (There's one typo: s/ENOTCON/ENOTCONN).
>>
>> It seems not to work though; when I send a signal to my test
>> target process that is sleeping waiting for the notification
>> response, the process enters the uninterruptible D state.
>> Any thoughts?
> 
> Ah, yeah, I think I was completely misusing the wait API. I'll go change that.
> 
> (Btw, in general, for reports about hangs like that, it can be helpful
> to have the contents of /proc/$pid/stack. And for cases where CPUs are
> spinning, the relevant part from the output of the "L" sysrq, or
> something like that.)

Thanks for the tipcs!

> Also, I guess we can probably break this part of UAPI after all, since
> the only user of this interface seems to currently be completely
> broken in this case anyway? So I think we want the other
> implementation without the ->canceled_reqs logic after all.

Okay.

> I'm a bit on the fence now on whether non-blocking mode should use
> ENOTCONN or not... I guess if we returned ENOENT even when there are
> no more listeners, you'd have to disambiguate through the poll()
> revents, which would be kinda ugly?

I must confess, I'm not quite clear on which two cases you 
are trying to distinguish. Can you elaborate?

> I'll try to turn this into a proper patch submission...

Thank you!!

Cheers,

Michael


-- 
Michael Kerrisk
Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/
Linux/UNIX System Programming Training: http://man7.org/training/