linux-kernel - Re: pselect/etc semantics

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Date:   Thu, 30 May 2019 08:48:12 -0700
From:   Deepa Dinamani <deepa.kernel@...il.com>
To:     "Eric W. Biederman" <ebiederm@...ssion.com>
Cc:     Oleg Nesterov <oleg@...hat.com>, Al Viro <viro@...iv.linux.org.uk>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Arnd Bergmann <arnd@...db.de>, dbueso@...e.de, axboe@...nel.dk,
        Davidlohr Bueso <dave@...olabs.net>, Eric Wong <e@...24.org>,
        Jason Baron <jbaron@...mai.com>,
        Linux FS-devel Mailing List <linux-fsdevel@...r.kernel.org>,
        linux-aio <linux-aio@...ck.org>,
        Omar Kilani <omar.kilani@...il.com>,
        Thomas Gleixner <tglx@...utronix.de>, stable@...r.kernel.org
Subject: Re: pselect/etc semantics

> On May 30, 2019, at 8:38 AM, Eric W. Biederman <ebiederm@...ssion.com> wrote:
>
> ebiederm@...ssion.com (Eric W. Biederman) writes:
>
>> Which means I believe we have a semantically valid change in behavior
>> that is causing a regression.
>
> I haven't made a survey of all of the functions yet but
> fucntions return -ENORESTARTNOHAND will never return -EINTR and are
> immune from this problem.
>
> AKA pselect is fine.  While epoll_pwait can be affected.

This was my understanding as well.

> Has anyone contacted Omar Kilani to see if that is his issue?
> https://lore.kernel.org/lkml/CA+8F9hicnF=kvjXPZFQy=Pa2HJUS3JS+G9VswFHNQQynPMHGVQ@mail.gmail.com/

Omar was cc-ed when this regression was reported. I did cc him on fix
and asked if he could try it. We have not heard from him.

> So far the only regression report I am seeing is from Eric Wong.
> AKA https://lore.kernel.org/lkml/20190501021405.hfvd7ps623liu25i@dcvr/
> Are there any others?  How did we get to be talking about more
> than just epoll_pwait?

This is the only report that I know of. I’m not sure why people
started talking about pselect. I was also confused why instead of
reviewing the patch and discussing the fix, we ended up talking about
how to simplify the code. We have deviated much from what should have
been a code review.

-Deepa