linux-kernel - Re: [PATCH] bpf: Fix preempt_enable_no

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Message-ID: <CAHk-=wiw7dbrvnqHHw1f1GyKzn70Oi+3WJCJ85zh8X3QHsVsyA@mail.gmail.com>
Date:   Tue, 23 Apr 2019 13:45:17 -0700
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Waiman Long <longman@...hat.com>, Ingo Molnar <mingo@...hat.com>,
        Will Deacon <will.deacon@....com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Linux List Kernel Mailing <linux-kernel@...r.kernel.org>,
        "the arch/x86 maintainers" <x86@...nel.org>,
        Davidlohr Bueso <dave@...olabs.net>,
        Tim Chen <tim.c.chen@...ux.intel.com>,
        huang ying <huang.ying.caritas@...il.com>,
        Roman Gushchin <guro@...com>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>
Subject: Re: [PATCH] bpf: Fix preempt_enable_no_resched() abuse

On Tue, Apr 23, 2019 at 1:35 PM Peter Zijlstra <peterz@...radead.org> wrote:
>
> That one 'funnily' doesn't actually work; cond_resched() is a no-op on
> PREEMPT=y.

Uhhuh. I "knew" that, but it's one of those bitrotting things.

Which does make your argument stronger, of course. This is way too
easy to get wrong even if you think you are being careful.

I guess it could be another thing to check for with objtool, since you
have now gotten the experience with it ;)

                   Linus