linux-ext4 - Re: Aarch64 EXT4FS inode checksum failures - seems to be weak memory ordering issues

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Date:   Thu, 7 Jan 2021 22:20:38 +0100
From:   Arnd Bergmann <arnd@...nel.org>
To:     Russell King - ARM Linux admin <linux@...linux.org.uk>
Cc:     Will Deacon <will@...nel.org>, 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 Thu, Jan 7, 2021 at 2:37 PM Russell King - ARM Linux admin
<linux@...linux.org.uk> wrote:
> On Thu, Jan 07, 2021 at 02:16:25PM +0100, Arnd Bergmann wrote:
> > On Thu, Jan 7, 2021 at 1:47 PM Russell King - ARM Linux admin
> > <linux@...linux.org.uk> wrote:
>
> > The gcc bugzilla mentions backports into gcc-linaro, but I do not see
> > them in my git history.

Correction: I looked in the wrong branch, gcc-linaro does have it, as
does the Android gcc, which was recently still at 4.9 before they dropped it
in favor of clang.

> So, do we raise the minimum gcc version for the kernel as a whole to 5.1
> or just for aarch64?

I'd personally love to see gcc-5 as the global minimum version, as that
would let us finally use --std=gnu11 features instead of gnu89. [There are
a couple of useful features that are incompatible with gnu89, and
gnu99/gnu11 support in gcc didn't like the kernel sources]

If we make it arm64 specific, I'd propose only making it a build-time
warning instead of an error, as there are no other benefits to increasing
the minimum version if gcc-4.9 is still an option for other architectures,
and most gcc-4.9 users (Android, Red Hat and everyone using gcc-linaro)
have backported this bugfix already.

         Arnd