Re: [PATCH 1/5] eventpoll: Convert epoll_put_uevent() to scoped user access

[David Laight <david.laight.linux@gmail.com>]

On Tue, 10 Mar 2026 11:25:48 +0100
"Christophe Leroy (CS GROUP)" <chleroy@kernel.org> wrote:

> Le 10/03/2026 à 09:32, Eric Dumazet a écrit :
> > On Tue, Mar 10, 2026 at 9:29 AM Christophe Leroy (CS GROUP)
> > <chleroy@kernel.org> wrote:  
> >>
> >>
> >>
> >> Le 10/03/2026 à 08:54, renpanpan a écrit :  
> >>> [Vous ne recevez pas souvent de courriers de renpanpan@kylinos.cn. Découvrez pourquoi ceci est important à https://aka.ms/LearnAboutSenderIdentification ]
> >>>
> >>> From: Eric Dumazet <edumazet@google.com>
> >>>
> >>> Saves two function calls, and one stac/clac pair.
> >>>
> >>> stac/clac is rather expensive on older cpus like Zen 2.
> >>>
> >>> A synthetic network stress test gives a ~1.5% increase of pps
> >>> on AMD Zen 2.
> >>>
> >>> Signed-off-by: Eric Dumazet <edumazet@google.com>
> >>> Cc: Christophe Leroy <christophe.leroy@csgroup.eu>
> >>> Cc: Dave Hansen <dave.hansen@intel.com>
> >>> Cc: Kuniyuki Iwashima <kuniyu@google.com>
> >>> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
> >>> ---
> >>>    include/linux/eventpoll.h | 11 +++++++----
> >>>    1 file changed, 7 insertions(+), 4 deletions(-)
> >>>
> >>> diff --git a/include/linux/eventpoll.h b/include/linux/eventpoll.h
> >>> index ccb478eb174b..ea9ca0e4172a 100644
> >>> --- a/include/linux/eventpoll.h
> >>> +++ b/include/linux/eventpoll.h
> >>> @@ -82,11 +82,14 @@ static inline struct epoll_event __user *
> >>>    epoll_put_uevent(__poll_t revents, __u64 data,
> >>>                    struct epoll_event __user *uevent)
> >>>    {
> >>> -       if (__put_user(revents, &uevent->events) ||
> >>> -           __put_user(data, &uevent->data))
> >>> -               return NULL;
> >>> -
> >>> +       scoped_user_write_access_size(uevent, sizeof(*uevent), efault) {  
> >>
> >> As already mentionned this could be simplified:  
> > 
> > Note the patch was already merged in Linus tree.
> > 
> > Honestly having two different macros while we have 4 users for both
> > of them seems a bit overkill to me.  
> 
> There have at the time beeing (v7.0-rc3) 66 caller of 
> user_...access_begin(), I expect most of them being converted to scoped 
> user access over time. In addition the simplicity of scoped user access 
> should help grow the numbre of users of user access by block.
> 
> I find it quite convenient to not have to add the size when it can be 
> extracted from the pointer type.

Lets see if it possible to support both:
	foo(ptr, label)
and:
	foo(ptr, size, label)

#define foo(p, ...) foo_1(p, __VA_ARGS__, sizeof *p)
#define foo_1(p, s_or_l, l_or_ps, ...) \
	foo_2(p, __VA_OPT__(s_or_l, l_or_ps, foo_x(__VA_ARGS__)) l_or_ps, s_or_pl)
#define foo_x(one_arg)
#define foo_2(p, s, l, ...) foo_real(p, s, l)

untested - but might work!
(foo_x() is there to error foo(a, b, c, d))

	David

> 
> Christophe
>