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From:   Marco Elver <elver@google.com>
Date:   Sat, 1 May 2021 18:26:17 +0200
Message-ID: <CANpmjNMtM7JyxTiA-QpEmqd0MuQ+uZTjfZ3+_r4D=rrGpFU8RA@mail.gmail.com>
Subject: Re: [RFC][PATCH 0/3] signal: Move si_trapno into the _si_fault union
To:     "Eric W. Biederman" <ebiederm@xmission.com>
Cc:     Arnd Bergmann <arnd@arndb.de>, Florian Weimer <fweimer@redhat.com>,
        "David S. Miller" <davem@davemloft.net>,
        Peter Zijlstra <peterz@infradead.org>,
        Ingo Molnar <mingo@kernel.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        Peter Collingbourne <pcc@google.com>,
        Dmitry Vyukov <dvyukov@google.com>,
        Alexander Potapenko <glider@google.com>,
        sparclinux <sparclinux@vger.kernel.org>,
        linux-arch <linux-arch@vger.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Linux API <linux-api@vger.kernel.org>,
        kasan-dev <kasan-dev@googlegroups.com>
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On Sat, 1 May 2021 at 02:37, Marco Elver <elver@google.com> wrote:
> On Sat, 1 May 2021 at 01:48, Eric W. Biederman <ebiederm@xmission.com> wrote:
> >
> > Well with 7 patches instead of 3 that was a little more than I thought
> > I was going to send.
> >
> > However that does demonstrate what I am thinking, and I think most of
> > the changes are reasonable at this point.
> >
> > I am very curious how synchronous this all is, because if this code
> > is truly synchronous updating signalfd to handle this class of signal
> > doesn't really make sense.

Just a note on this: the reason for adding signalfd support was based
on the comment at SIL_FAULT_PKUERR:

>                 /*
>                   * Fall through to the SIL_FAULT case.  Both SIL_FAULT_BNDERR
>                   * and SIL_FAULT_PKUERR are only generated by faults that
>                   * deliver them synchronously to userspace.  In case someone
>                   * injects one of these signals and signalfd catches it treat
>                   * it as SIL_FAULT.
>                   */

The same would hold for SIL_FAULT_PERF_EVENT, where somebody injects
(re-injects perhaps?) such an event. But otherwise, yes,
non-synchronous handling of SIGTRAP/TRAP_PERF is pretty useless for
almost all usecases I can think of.

Thanks,
-- Marco