linux-kernel - Re: Aarch64 EXT4FS inode checksum failures - seems to be weak memory ordering issues

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Message-ID: <CAK8P3a2w2u8pcQJue3OveDckJNkGmwzVdfOM-VEXShQEw8EOzw@mail.gmail.com>
Date:   Fri, 8 Jan 2021 21:22:18 +0100
From:   Arnd Bergmann <arnd@...nel.org>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     Will Deacon <will@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Russell King - ARM Linux admin <linux@...linux.org.uk>,
        linux-toolchains@...r.kernel.org,
        Mark Rutland <mark.rutland@....com>,
        "Theodore Ts'o" <tytso@....edu>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Andreas Dilger <adilger.kernel@...ger.ca>,
        Ext4 Developers List <linux-ext4@...r.kernel.org>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>
Subject: Re: Aarch64 EXT4FS inode checksum failures - seems to be weak memory
 ordering issues

On Fri, Jan 8, 2021 at 9:02 PM Linus Torvalds
<torvalds@...ux-foundation.org> wrote:
> On Fri, Jan 8, 2021 at 1:27 AM Will Deacon <will@...nel.org> wrote:
> >
> > On Fri, Jan 08, 2021 at 10:21:54AM +0100, Peter Zijlstra wrote:
> > > On Thu, Jan 07, 2021 at 10:20:38PM +0100, Arnd Bergmann wrote:
> > > > On Thu, Jan 7, 2021 at 2:37 PM Russell King - ARM Linux admin
>
> I appreciate Arnd pointing out "--std=gnu11", though. What are the
> actual relevant language improvements?
>
> Variable declarations in for-loops is the only one I can think of. I
> think that would clean up some code (and some macros), but might not
> be compelling on its own.

I think that was the main one, as most of --std=c11 is already part
of --std=gnu89 as a gnu extension. There were a few things that
came up with clang porting, as clang is somewhat closer to gnu11
than to gnu89, but I don't remember exactly what that was.

I would still like to improve READ_ONCE()/get_user()/cmpxchg()
further using __auto_type and _Generic where possible, but I think
that was already supported in gcc-4.9, and does not require gcc-5.

       Arnd