linux-kernel - Re: [GIT PULL] pipe: nonblocking rw for io

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Message-ID: <20230425194910.GA1350354@hirez.programming.kicks-ass.net>
Date:   Tue, 25 Apr 2023 21:49:10 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     Jens Axboe <axboe@...nel.dk>, Ingo Molnar <mingo@...hat.com>,
        Will Deacon <will@...nel.org>,
        Christian Brauner <brauner@...nel.org>,
        linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
        Mark Rutland <mark.rutland@....com>
Subject: Re: [GIT PULL] pipe: nonblocking rw for io_uring

On Tue, Apr 25, 2023 at 10:20:31AM -0700, Linus Torvalds wrote:

> But the more I look at it, the more I'm convinced that our pattern of
> 
>         old = READ_ONCE(rq->fence.error);
>         do {
>                 if (fatal_error(old))
>                         return false;
>         } while (!try_cmpxchg(&rq->fence.error, &old, error));
> 
> (to pick one random user) is simply horribly wrong.

The last time this came up I shared your view however Mark argued for
the READ_ONCE() thusly:

  https://lore.kernel.org/all/Y71LoCIl+IFdy9D8@FVFF77S0Q05N/T/#u