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

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Date:   Thu, 7 Jan 2021 22:48:05 +0100
From:   Arnd Bergmann <arnd@...nel.org>
To:     "Theodore Ts'o" <tytso@....edu>
Cc:     Russell King - ARM Linux admin <linux@...linux.org.uk>,
        Will Deacon <will@...nel.org>,
        linux-toolchains@...r.kernel.org,
        Mark Rutland <mark.rutland@....com>,
        "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 5:27 PM Theodore Ts'o <tytso@....edu> wrote:
>
> On Thu, Jan 07, 2021 at 01:37:47PM +0000, Russell King - ARM Linux admin wrote:
> > > The gcc bugzilla mentions backports into gcc-linaro, but I do not see
> > > them in my git history.
> >
> > So, do we raise the minimum gcc version for the kernel as a whole to 5.1
> > or just for aarch64?
>
> Russell, Arnd, thanks so much for tracking down the root cause of the
> bug!

There is one more thing that I wondered about when looking through
the ext4 code: Should it just call the crc32c_le() function directly
instead of going through the crypto layer? It seems that with Ard's
rework from 2018, that can just call the underlying architecture specific
implementation anyway.

> I will note that RHEL 7 uses gcc 4.8.  I personally don't have an
> objections to requiring developers using RHEL 7 to have to install a
> more modern gcc (since I use Debian Testing and gcc 10.2.1, myself,
> and gcc 5.1 is so five years ago :-), but I could imagine that being
> considered inconvenient for some.

The main users of gcc-4.9 that I recall from previous discussions
were Android and Debian 8, but both of them are done now: Debian 8
has reached its end of life last summer, and Android uses clang
for building new kernels.

       Arnd