linux-kernel - Re: [PATCH] mm: remove unintentional voluntary preemption in get_mmap_lock

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Message-ID: <CAHk-=wh=cECn7SLr31VXwtJq-wYnt5+VcERnvAmEVktdEKqR=w@mail.gmail.com>
Date:   Sun, 20 Aug 2023 14:47:41 +0200
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     Mateusz Guzik <mjguzik@...il.com>
Cc:     Matthew Wilcox <willy@...radead.org>, akpm@...ux-foundation.org,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCH] mm: remove unintentional voluntary preemption in get_mmap_lock_carefully

On Sun, 20 Aug 2023 at 14:41, Mateusz Guzik <mjguzik@...il.com> wrote:
>
> On 8/20/23, Matthew Wilcox <willy@...radead.org> wrote:
> >
> > Except now we search the exception tables every time we call it.
> > The now-deleted comment (c2508ec5a58d) suggests this is slow:

Yeah, that was the intent.

But I agree that we should basically avoid trying to sleep just as we
got the lock.

> My first patch looked like this:

Well, that's disgusting and strange.

> -               might_sleep();
> +#if defined(CONFIG_DEBUG_ATOMIC_SLEEP)
> +               __might_sleep(__FILE__, __LINE__);
> +#endif

Why would you have that strange #ifdef? __might_sleep() just goes away
without that debug option anyway.

But without that odd ifdef, I think it's fine.

            Linus