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From: "Darrick J. Wong" <darrick.wong@oracle.com>
To: Eric Biggers <ebiggers@kernel.org>
Cc: Arnd Bergmann <arnd@kernel.org>, "Theodore Ts'o" <tytso@mit.edu>,
	Russell King - ARM Linux admin <linux@armlinux.org.uk>,
	Will Deacon <will@kernel.org>,
	linux-toolchains@vger.kernel.org,
	Mark Rutland <mark.rutland@arm.com>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	Andreas Dilger <adilger.kernel@dilger.ca>,
	Ext4 Developers List <linux-ext4@vger.kernel.org>,
	Linux ARM <linux-arm-kernel@lists.infradead.org>
Subject: Re: Aarch64 EXT4FS inode checksum failures - seems to be weak memory ordering issues
Date: Thu, 7 Jan 2021 15:53:28 -0800	[thread overview]
Message-ID: <20210107235328.GI6908@magnolia> (raw)
In-Reply-To: <X/eK5xIMK5yZ2/tl@gmail.com>

On Thu, Jan 07, 2021 at 02:27:51PM -0800, Eric Biggers wrote:
> On Thu, Jan 07, 2021 at 10:48:05PM +0100, Arnd Bergmann wrote:
> > On Thu, Jan 7, 2021 at 5:27 PM Theodore Ts'o <tytso@mit.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.
> > 
> 
> It looks like that would work, although note that crc32c_le() uses the shash API
> too, so it isn't any more "direct" than what ext4 does now.

Yes.

> Also, a potential issue is that the implementation of crc32c that crc32c_le()
> uses might be chosen too early if the architecture-specific implementation of
> crc32c is compiled as a module (e.g. crc32c-intel.ko).

This was the primary reason I chose to do it this way for ext4.

The other is that ext4 didn't use crc32c before metadata_csum, so
there's no point in pulling in the crypto layer if you're only going to
use older ext2 or ext3 filesystems.  That was 2010, maybe people have
stopped doing that?

> There are two ways this
> could be fixed -- either by making it a proper library API like blake2s() that
> can call the architecture-specific code directly, or by reconfiguring things
> when a new crypto module is loaded (like what lib/crc-t10dif.c does).

Though I would like to see the library functions gain the ability to use
whatever is the fastest mechanism available once we can be reasonably
certain that all the platform-specific drivers have been loaded.

That said, IIRC most distros compile all of them into their
(increasingly large) vmlinuz files so maybe this isn't much of practical
concern?

--D
> 
> Until one of those is done, switching to crc32c_le() might cause performance
> regressions.
> 
> - Eric

WARNING: multiple messages have this Message-ID
From: "Darrick J. Wong" <darrick.wong@oracle.com>
To: Eric Biggers <ebiggers@kernel.org>
Cc: Mark Rutland <mark.rutland@arm.com>,
	Arnd Bergmann <arnd@kernel.org>, Theodore Ts'o <tytso@mit.edu>,
	Russell King - ARM Linux admin <linux@armlinux.org.uk>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	Andreas Dilger <adilger.kernel@dilger.ca>,
	linux-toolchains@vger.kernel.org,
	Ext4 Developers List <linux-ext4@vger.kernel.org>,
	Will Deacon <will@kernel.org>,
	Linux ARM <linux-arm-kernel@lists.infradead.org>
Subject: Re: Aarch64 EXT4FS inode checksum failures - seems to be weak memory ordering issues
Date: Thu, 7 Jan 2021 15:53:28 -0800	[thread overview]
Message-ID: <20210107235328.GI6908@magnolia> (raw)
In-Reply-To: <X/eK5xIMK5yZ2/tl@gmail.com>

On Thu, Jan 07, 2021 at 02:27:51PM -0800, Eric Biggers wrote:
> On Thu, Jan 07, 2021 at 10:48:05PM +0100, Arnd Bergmann wrote:
> > On Thu, Jan 7, 2021 at 5:27 PM Theodore Ts'o <tytso@mit.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.
> > 
> 
> It looks like that would work, although note that crc32c_le() uses the shash API
> too, so it isn't any more "direct" than what ext4 does now.

Yes.

> Also, a potential issue is that the implementation of crc32c that crc32c_le()
> uses might be chosen too early if the architecture-specific implementation of
> crc32c is compiled as a module (e.g. crc32c-intel.ko).

This was the primary reason I chose to do it this way for ext4.

The other is that ext4 didn't use crc32c before metadata_csum, so
there's no point in pulling in the crypto layer if you're only going to
use older ext2 or ext3 filesystems.  That was 2010, maybe people have
stopped doing that?

> There are two ways this
> could be fixed -- either by making it a proper library API like blake2s() that
> can call the architecture-specific code directly, or by reconfiguring things
> when a new crypto module is loaded (like what lib/crc-t10dif.c does).

Though I would like to see the library functions gain the ability to use
whatever is the fastest mechanism available once we can be reasonably
certain that all the platform-specific drivers have been loaded.

That said, IIRC most distros compile all of them into their
(increasingly large) vmlinuz files so maybe this isn't much of practical
concern?

--D
> 
> Until one of those is done, switching to crc32c_le() might cause performance
> regressions.
> 
> - Eric

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http://lists.infradead.org/mailman/listinfo/linux-arm-kernel

  reply	other threads:[~2021-01-07 23:54 UTC|newest]

Thread overview: 73+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-01-05 15:47 Russell King - ARM Linux admin
2021-01-05 15:47 ` Russell King - ARM Linux admin
2021-01-05 18:27 ` Darrick J. Wong
2021-01-05 18:27   ` Darrick J. Wong
2021-01-05 19:50   ` Russell King - ARM Linux admin
2021-01-05 19:50     ` Russell King - ARM Linux admin
2021-01-06 11:53 ` Mark Rutland
2021-01-06 11:53   ` Mark Rutland
2021-01-06 12:13   ` Russell King - ARM Linux admin
2021-01-06 12:13     ` Russell King - ARM Linux admin
2021-01-06 13:52   ` Russell King - ARM Linux admin
2021-01-06 17:20     ` Will Deacon
2021-01-06 17:20       ` Will Deacon
2021-01-06 17:46       ` Russell King - ARM Linux admin
2021-01-06 17:46         ` Russell King - ARM Linux admin
2021-01-06 21:04       ` Arnd Bergmann
2021-01-06 21:04         ` Arnd Bergmann
2021-01-06 22:00         ` Arnd Bergmann
2021-01-06 22:00           ` Arnd Bergmann
2021-01-06 22:32       ` Russell King - ARM Linux admin
2021-01-06 22:32         ` Russell King - ARM Linux admin
2021-01-07 11:18         ` Russell King - ARM Linux admin
2021-01-07 11:18           ` Russell King - ARM Linux admin
2021-01-07 12:45           ` Russell King - ARM Linux admin
2021-01-07 12:45             ` Russell King - ARM Linux admin
2021-01-07 13:16             ` Arnd Bergmann
2021-01-07 13:16               ` Arnd Bergmann
2021-01-07 13:37               ` Russell King - ARM Linux admin
2021-01-07 13:37                 ` Russell King - ARM Linux admin
2021-01-07 16:27                 ` Theodore Ts'o
2021-01-07 16:27                   ` Theodore Ts'o
2021-01-07 17:00                   ` Florian Weimer
2021-01-07 17:00                     ` Florian Weimer
2021-01-07 21:48                   ` Arnd Bergmann
2021-01-07 21:48                     ` Arnd Bergmann
2021-01-07 22:14                     ` Russell King - ARM Linux admin
2021-01-07 22:14                       ` Russell King - ARM Linux admin
2021-01-07 22:41                       ` Eric Biggers
2021-01-07 22:41                         ` Eric Biggers
2021-01-08  8:21                         ` Ard Biesheuvel
2021-01-08  8:21                           ` Ard Biesheuvel
2021-01-07 22:27                     ` Eric Biggers
2021-01-07 22:27                       ` Eric Biggers
2021-01-07 23:53                       ` Darrick J. Wong [this message]
2021-01-07 23:53                         ` Darrick J. Wong
2021-01-08  8:05                         ` Arnd Bergmann
2021-01-08  8:05                           ` Arnd Bergmann
2021-01-08  9:13                   ` Peter Zijlstra
2021-01-08  9:13                     ` Peter Zijlstra
2021-01-08 10:31                   ` Pavel Machek
2021-01-08 10:31                     ` Pavel Machek
2021-01-07 21:20                 ` Arnd Bergmann
2021-01-07 21:20                   ` Arnd Bergmann
2021-01-08  9:21                   ` Peter Zijlstra
2021-01-08  9:21                     ` Peter Zijlstra
2021-01-08  9:26                     ` Will Deacon
2021-01-08  9:26                       ` Will Deacon
2021-01-08 20:02                       ` Linus Torvalds
2021-01-08 20:02                         ` Linus Torvalds
2021-01-08 20:22                         ` Arnd Bergmann
2021-01-08 20:22                           ` Arnd Bergmann
2021-01-08 21:20                           ` Nick Desaulniers
2021-01-08 21:20                             ` Nick Desaulniers
2021-01-08 20:29                         ` Russell King - ARM Linux admin
2021-01-08 20:29                           ` Russell King - ARM Linux admin
2021-01-12 13:20                         ` Lukas Wunner
2021-01-12 13:31                           ` Florian Weimer
2021-01-12 13:31                             ` Florian Weimer
2021-01-12 13:46                             ` David Laight
2021-01-12 13:46                               ` David Laight
2021-01-12 17:28                           ` Linus Torvalds
2021-01-12 17:28                             ` Linus Torvalds
2021-01-14 13:13                             ` Lukas Wunner

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