From: Oleg Nesterov <oleg@redhat.com>
To: "Eric W. Biederman" <ebiederm@xmission.com>
Cc: Dmitry Vyukov <dvyukov@google.com>,
Thomas Gleixner <tglx@linutronix.de>,
Ingo Molnar <mingo@redhat.com>,
Peter Zijlstra <peterz@infradead.org>,
LKML <linux-kernel@vger.kernel.org>,
Arnaldo Carvalho de Melo <acme@kernel.org>,
Alexander Shishkin <alexander.shishkin@linux.intel.com>,
jolsa@redhat.com, Namhyung Kim <namhyung@kernel.org>,
luca abeni <luca.abeni@santannapisa.it>,
syzkaller <syzkaller@googlegroups.com>
Subject: Re: [PATCH 2/2] signal: Better detection of synchronous signals
Date: Tue, 12 Feb 2019 18:21:04 +0100 [thread overview]
Message-ID: <20190212172104.GC29263@redhat.com> (raw)
In-Reply-To: <87va1pj2n0.fsf@xmission.com>
On 02/11, Eric W. Biederman wrote:
>
> Oleg Nesterov <oleg@redhat.com> writes:
>
> >> + /*
> >> + * Check if there is another siginfo for the same signal.
> >> + */
> >> + list_for_each_entry_continue(q, &pending->list, list) {
> >> + if (q->info.si_signo == sync->info.si_signo)
> >> + goto still_pending;
> >> + }
> >
> > But this must not be possible? SYNCHRONOUS_MASK doesn't include real-time
> > signals, we can't have 2 siginfo's for the same signal < SIGRTMIN.
>
> Yes for that reason it should be safe to strip that logic out at the
> moment. I overlooked that when writing the code.
>
> However. I am not certain that is a limit we actually want to honor
> with synchronous signals. As it results in a louzy quality of
> implementation.
>
> We start with an instruction in the program being debugged. In
> principle before that instruction starts we know that no signals
> are pending because they were not delivered to that process.
>
> If we for some reason send signal A to the process and at the same time
> hit a fault that is reported as signal A. It is currently a race which
> one wins. I think we could legitimately say that the fault happened
> before signal A was enqueued, and deliver both. It is a bit murkier if
> signal A was blocked.
>
> If we let the enqueued signal A win (as we do today) we have SA_SIGNFO
> that is not useful for describing the fault the instruction generated.
> Which is a really lousy quality of implementation.
I doubt this would be really useful but this doesn't matter right now,
> Which is a long way of saying I think that hunk of code is useful as it
> allows us the possibility of fixing a lousy quality of implementation in
> our code today.
If we ever rework the legacy_queue() logic we can easily add this hunk back.
Until then it complicates the code for no reason imo, just to confuse the reader.
Oleg.
next prev parent reply other threads:[~2019-02-12 17:21 UTC|newest]
Thread overview: 31+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-02-01 16:48 perf_event_open+clone = unkillable process Dmitry Vyukov
2019-02-01 17:06 ` Dmitry Vyukov
2019-02-02 18:30 ` Jiri Olsa
2019-02-03 15:21 ` Jiri Olsa
2019-02-04 9:27 ` Thomas Gleixner
2019-02-04 9:38 ` Dmitry Vyukov
2019-02-04 17:38 ` Thomas Gleixner
2019-02-05 3:00 ` Eric W. Biederman
2019-02-05 4:27 ` Eric W. Biederman
2019-02-05 6:07 ` Eric W. Biederman
2019-02-05 15:26 ` [RFC][PATCH] signal: Store pending signal exit in tsk.jobctl not in tsk.pending Eric W. Biederman
2019-02-06 12:09 ` Dmitry Vyukov
2019-02-06 21:47 ` Eric W. Biederman
2019-02-06 18:07 ` Oleg Nesterov
2019-02-06 22:25 ` Eric W. Biederman
2019-02-07 6:42 ` [PATCH 0/2]: Fixing unkillable processes caused by SIGHUP timers Eric W. Biederman
2019-02-07 6:43 ` [PATCH 1/2] signal: Always notice exiting tasks Eric W. Biederman
2019-02-11 14:13 ` Oleg Nesterov
2019-02-12 0:42 ` Eric W. Biederman
2019-02-12 8:18 ` Eric W. Biederman
2019-02-12 16:50 ` Oleg Nesterov
2019-02-13 3:58 ` Eric W. Biederman
2019-02-13 4:09 ` [PATCH] signal: Restore the stop PTRACE_EVENT_EXIT Eric W. Biederman
2019-02-13 13:55 ` Oleg Nesterov
2019-02-13 14:38 ` Oleg Nesterov
2019-02-13 14:58 ` Eric W. Biederman
2019-02-07 6:44 ` [PATCH 2/2] signal: Better detection of synchronous signals Eric W. Biederman
2019-02-11 15:18 ` Oleg Nesterov
2019-02-12 0:01 ` Eric W. Biederman
2019-02-12 17:21 ` Oleg Nesterov [this message]
2019-02-07 11:46 ` [PATCH 0/2]: Fixing unkillable processes caused by SIGHUP timers Dmitry Vyukov
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