linux-kernel - Re: [PATCH] pipe_read: don't wake up the writer if the pipe is still full

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <874j065w1v.fsf@prevas.dk>
Date: Thu, 06 Mar 2025 10:48:44 +0100
From: Rasmus Villemoes <ravi@...vas.dk>
To: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Oleg Nesterov <oleg@...hat.com>,  Mateusz Guzik <mjguzik@...il.com>,  K
 Prateek Nayak <kprateek.nayak@....com>,  "Sapkal, Swapnil"
 <swapnil.sapkal@....com>,  Manfred Spraul <manfred@...orfullife.com>,
  Christian Brauner <brauner@...nel.org>,  David Howells
 <dhowells@...hat.com>,  WangYuli <wangyuli@...ontech.com>,
  linux-fsdevel@...r.kernel.org,  linux-kernel@...r.kernel.org,  "Shenoy,
 Gautham Ranjal" <gautham.shenoy@....com>,  Neeraj.Upadhyay@....com,
  Ananth.narayan@....com,  Matthew Wilcox <willy@...radead.org>, Nick
 Desaulniers <ndesaulniers@...gle.com>
Subject: Re: [PATCH] pipe_read: don't wake up the writer if the pipe is
 still full

On Wed, Mar 05 2025, Linus Torvalds <torvalds@...ux-foundation.org> wrote:

> On Wed, 5 Mar 2025 at 05:31, Rasmus Villemoes <ravi@...vas.dk> wrote:
>>
>> On Mon, Mar 03 2025, Linus Torvalds <torvalds@...ux-foundation.org> wrote:
>>
>> > +/*
>> > + * We have to declare this outside 'struct pipe_inode_info',
>> > + * but then we can't use 'union pipe_index' for an anonymous
>> > + * union, so we end up having to duplicate this declaration
>> > + * below. Annoying.
>> > + */
>> > +union pipe_index {
>> > +     unsigned long head_tail;
>> > +     struct {
>> > +             pipe_index_t head;
>> > +             pipe_index_t tail;
>> > +     };
>> > +};
>> > +
>>
>> -fms-extensions ? Willy wanted to add that for use in mm/ some years ago
>> [*], and it has come up a few other times as well.
>>
>> [*] https://lore.kernel.org/lkml/20180419152817.GD25406@bombadil.infradead.org/
>
> Oh, I was unaware of that extension, and yes, it would have been
> lovely here, avoiding that duplicate union declaration.
>
> But it does require clang support - I see that clang has a
> '-fms-extensions' as well, so it's presumably there.

Yes, it seems they do have it, but for mysterious reasons saying
-fms-extensions is not quite enough to convince clang that one does
intend to use that MS extension, one also has to say
-Wno-microsoft-anon-tag, or it complains

warning: anonymous unions are a Microsoft extension [-Wmicrosoft-anon-tag]

Also, the warning text is somewhat misleading; anon unions itself have
certainly been a gcc extension since forever, and nowadays a C11 thing,
and clang has a separate -Wpedantic warning for that when using
-std=c99:

warning: anonymous unions are a C11 extension [-Wc11-extensions]

The -W flag name actually suggests an improvement to the warning
"_tagged_ anonymous unions are a Microsoft extension", but I really
wonder why -fms-extensions isn't sufficient to silence that in the first
place. Also, the warning seems to be on by default; it's not some
-Wextra or -Wpedantic thing.

cc += Nick

Rasmus