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Date: Fri, 8 Jan 2021 20:29:24 +0000 From: Russell King - ARM Linux admin <linux@...linux.org.uk> To: Linus Torvalds <torvalds@...ux-foundation.org> Cc: Will Deacon <will@...nel.org>, Peter Zijlstra <peterz@...radead.org>, Arnd Bergmann <arnd@...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 Fri, Jan 08, 2021 at 12:02:53PM -0800, Linus Torvalds wrote: > Well, honestly, I'm always in favor of having people not use ancient > compilers, but both of the issues at hand do seem to be specific to > arm64. > > The "gcc before 5.1 generates incorrect stack pointer writes on arm64" > sounds pretty much deadly, and I think means that yes, for arm64 we > simply need to require 5.1 or newer. > > I also suspect there is much less reason to use old gcc's on arm64. I > can't imagine that people really run very old setups, Is some old RHEL > version even relevant for arm64? For me, six years old for a compiler is really not "very old" - and, when I first encountered this problem, it was over 12 months ago. Apart from the kernel, I am not in the habbit of upgrading stuff for the sake of upgrading - I tend to stick with what I have and what works. Not everyone on this planet has a desire to have the latest and greatest all the time. Since then, I've _not_ wanted to change the compiler in case the problem vanishes without explanation - it had the feeling of being way more serious than a compiler bug, potentially a memory ordering bug. It took about a year just to start being able to work out what was going on - it would take up to about three months to show for me, and when it did, it spat out an ext4 inode checksum error and made the rootfs read-only. To "hide" that by upgrading the compiler, and then to be in the situation where you do not trust any aarch64 machine with your data is no real solution. That's exactly where I was until this had been found. The aarch64 architecture had completely lost my trust as a viable computing platform - and I was at the point of considering disposing of all my aarch64 hardware and replacing it with x86. -- RMK's Patch system: https://www.armlinux.org.uk/developer/patches/ FTTP is here! 40Mbps down 10Mbps up. Decent connectivity at last!
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