linux-kernel - Re: [PATCH bpf-next v4 2/4] uaccess: Define pagefault lock guard

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Message-ID: <CAEf4BzbggjOmEziyLjSRSsEQzLMMXQGoEJ6SODVF2exLR1S9UQ@mail.gmail.com>
Date: Fri, 9 May 2025 11:20:48 -0700
From: Andrii Nakryiko <andrii.nakryiko@...il.com>
To: Matt Bobrowski <mattbobrowski@...gle.com>
Cc: Viktor Malik <vmalik@...hat.com>, bpf@...r.kernel.org, 
	Alexei Starovoitov <ast@...nel.org>, Daniel Borkmann <daniel@...earbox.net>, 
	Andrii Nakryiko <andrii@...nel.org>, Martin KaFai Lau <martin.lau@...ux.dev>, 
	Eduard Zingerman <eddyz87@...il.com>, Song Liu <song@...nel.org>, 
	Yonghong Song <yonghong.song@...ux.dev>, John Fastabend <john.fastabend@...il.com>, 
	KP Singh <kpsingh@...nel.org>, Stanislav Fomichev <sdf@...ichev.me>, Hao Luo <haoluo@...gle.com>, 
	Jiri Olsa <jolsa@...nel.org>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH bpf-next v4 2/4] uaccess: Define pagefault lock guard

On Thu, May 8, 2025 at 3:01 AM Matt Bobrowski <mattbobrowski@...gle.com> wrote:
>
> On Wed, May 07, 2025 at 08:40:37AM +0200, Viktor Malik wrote:
> > Define a pagefault lock guard which allows to simplify functions that
> > need to disable page faults.
> >
> > Signed-off-by: Viktor Malik <vmalik@...hat.com>
> > ---
> >  include/linux/uaccess.h | 2 ++
> >  1 file changed, 2 insertions(+)
> >
> > diff --git a/include/linux/uaccess.h b/include/linux/uaccess.h
> > index 7c06f4795670..1beb5b395d81 100644
> > --- a/include/linux/uaccess.h
> > +++ b/include/linux/uaccess.h
> > @@ -296,6 +296,8 @@ static inline bool pagefault_disabled(void)
> >   */
> >  #define faulthandler_disabled() (pagefault_disabled() || in_atomic())
> >
> > +DEFINE_LOCK_GUARD_0(pagefault, pagefault_disable(), pagefault_enable())
>
> I can't help but mention that naming this scope-based cleanup helper
> `pagefault` just seems overly ambiguous. That's just me though...

I do see the concern, but

DEFINE_LOCK_GUARD_0(preempt, preempt_disable(), preempt_enable())
DEFINE_LOCK_GUARD_0(irq, local_irq_disable(), local_irq_enable())

so we are just staying consistent here? But also "guard (against) the
pagefault" does (internally) read somewhat meaningfully, no?