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

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Message-ID: <CAHk-=wiQ8g+B0bCPJ9fxZ+Oa0LPAUAyryw9i+-fBUe72LoA+QQ@mail.gmail.com>
Date:   Mon, 24 Apr 2023 14:37:37 -0700
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     Jens Axboe <axboe@...nel.dk>
Cc:     Christian Brauner <brauner@...nel.org>,
        linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [GIT PULL] pipe: nonblocking rw for io_uring

On Mon, Apr 24, 2023 at 2:22 PM Jens Axboe <axboe@...nel.dk> wrote:
>
> If we don't ever wait for IO with the pipe lock held, then we can skip
> the conditional locking. But with splice, that's not at all the case! We
> most certainly wait for IO there with the pipe lock held.

I think that then needs to just be fixed.

I really think that trylock due to "nonblocking" IO is fundamentally
wrong. Thinking that you need it is just a sign of something else
being very wrong.

That "very wrong" thing might well be splice then not honoring
non-blocking IO on a non-blocking pipe.

And I completely refuse to add that trylock hack to paper that over.
The pipe lock is *not* meant for IO.

             Linus