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Date:   Mon, 12 Jul 2021 21:16:33 +0200 (CEST)
From:   Jan Engelhardt <jengelh@inai.de>
To:     Suren Baghdasaryan <surenb@google.com>
cc:     Florian Weimer <fweimer@redhat.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Michal Hocko <mhocko@kernel.org>,
        Michal Hocko <mhocko@suse.com>,
        David Rientjes <rientjes@google.com>,
        Matthew Wilcox <willy@infradead.org>,
        Johannes Weiner <hannes@cmpxchg.org>,
        Roman Gushchin <guro@fb.com>, Rik van Riel <riel@surriel.com>,
        Minchan Kim <minchan@kernel.org>,
        Christian Brauner <christian@brauner.io>,
        Christoph Hellwig <hch@infradead.org>,
        Oleg Nesterov <oleg@redhat.com>,
        David Hildenbrand <david@redhat.com>,
        Jann Horn <jannh@google.com>,
        Shakeel Butt <shakeelb@google.com>,
        Tim Murray <timmurray@google.com>,
        Linux API <linux-api@vger.kernel.org>,
        linux-mm <linux-mm@kvack.org>,
        LKML <linux-kernel@vger.kernel.org>,
        kernel-team <kernel-team@android.com>
Subject: Re: [PATCH 1/1] mm: introduce process_reap system call
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On Monday 2021-07-12 20:39, Suren Baghdasaryan wrote:
>>
>> The way I understood the request is that a userspace program (or perhaps two,
>> if so desired) should issue _two_ calls, one to deliver the signal,
>> one to perform the reap portion:
>>
>>         uinfo.si_code = SI_QUEUE;
>>         sigqueue(pid, SIGKILL, &uinfo);
>>         uinfo.si_code = SI_REAP;
>>         sigqueue(pid, SIGKILL, &uinfo);
>
>This approach would still lead to the same discussion: by design,
>sigqueue/kill/pidfd_send_signal deliver the signal but do not wait for
>the signal to be processed by the recipient.

Oh, so the only reason not to do that is because there is some POSIX
specification that says the sigqueue API should be non-waiting for all
possible parameter values (with an implied "present and future
values!"), not because there's some hurdle to actually add a wait
inside within rt_sigqueueinfo if the REAP flag is set.
Gotcha.