Messages in this thread | | | Date | Tue, 12 Feb 2019 18:21:04 +0100 | From | Oleg Nesterov <> | Subject | Re: [PATCH 2/2] signal: Better detection of synchronous signals |
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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.
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