linux-kernel - Re: [GIT PULL] sigqueue cache fix

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Message-ID: <CAHk-=wiJq0Ns7_AFRW+rvZcD_m+1t5cYgvQRO-Gbp8TEK1x1bQ@mail.gmail.com>
Date:   Sun, 27 Jun 2021 13:40:39 -0700
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     Ingo Molnar <mingo@...nel.org>,
        Christian Brauner <christian.brauner@...ntu.com>,
        Oleg Nesterov <oleg@...hat.com>
Cc:     Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Peter Zijlstra <peterz@...radead.org>,
        Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [GIT PULL] sigqueue cache fix

On Sun, Jun 27, 2021 at 11:52 AM Linus Torvalds
<torvalds@...ux-foundation.org> wrote:
>
> Ok, I may have confused myself looking at all this, but it does all
> make me think this is dodgy.

I also couldn't convince myself that the memory ordering is correct
for the _contents_ of the sigqueue entry that had its pointer cached,
although I suspect that is purely a theoretical concern (certainly a
non-issue on x86).

So I've reverted the sigqueue cache code, in that I haven't heard
anything back and I'm not going to delay 5.13 over something small and
easily undone like this.

It could be that my worries about this code are all entirely wrong,
and I'm missing something, in which case you can call me names and we
can reinstate the code with my apologies.

Anyway, I tried to distill my thoughts about what is going on - and
what the solutions might be - in the revert commit b4b27b9eed8e.

Again, maybe it's just me that is confused. But reverting seemed to be
the safest thing to do considering the timing of this all.

           Linus