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From: Jan Kara <jack@suse.cz>
To: Josh Triplett <josh@joshtriplett.org>
Cc: Jan Kara <jack@suse.cz>,
	Linus Torvalds <torvalds@linux-foundation.org>,
	Theodore Ts'o <tytso@mit.edu>,
	Andreas Dilger <adilger.kernel@dilger.ca>,
	Jan Kara <jack@suse.com>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	linux-ext4@vger.kernel.org
Subject: Re: ext4 regression in v5.9-rc2 from e7bfb5c9bb3d on ro fs with overlapped bitmaps
Date: Mon, 5 Oct 2020 18:19:41 +0200	[thread overview]
Message-ID: <20201005161941.GF4225@quack2.suse.cz> (raw)
In-Reply-To: <20201005101641.GA516771@localhost>

On Mon 05-10-20 03:16:41, Josh Triplett wrote:
> On Mon, Oct 05, 2020 at 11:46:01AM +0200, Jan Kara wrote:
> > On Mon 05-10-20 01:14:54, Josh Triplett wrote:
> > > Ran into an ext4 regression when testing upgrades to 5.9-rc kernels:
> > > 
> > > Commit e7bfb5c9bb3d ("ext4: handle add_system_zone() failure in
> > > ext4_setup_system_zone()") breaks mounting of read-only ext4 filesystems
> > > with intentionally overlapping bitmap blocks.
> > > 
> > > On an always-read-only filesystem explicitly marked with
> > > EXT4_FEATURE_RO_COMPAT_SHARED_BLOCKS, prior to that commit, it's safe to
> > > point all the block and inode bitmaps to a single block of all 1s,
> > > because a read-only filesystem will never allocate or free any blocks or
> > > inodes.
> > > However, after that commit, the block validity check rejects such
> > > filesystems with -EUCLEAN and "failed to initialize system zone (-117)".
> > > This causes systems that previously worked correctly to fail when
> > > upgrading to v5.9-rc2 or later.
> > > 
> > > This was obviously a bugfix, and I'm not suggesting that it should be
> > > reverted; it looks like this effectively worked by accident before,
> > > because the block_validity check wasn't fully functional. However, this
> > > does break real systems, and I'd like to get some kind of regression fix
> > > in before 5.9 final if possible. I think it would suffice to make
> > > block_validity default to false if and only if
> > > EXT4_FEATURE_RO_COMPAT_SHARED_BLOCKS is set.
> > > 
> > > Does that seem like a reasonable fix?
> > 
> > Well, but EXT4_FEATURE_RO_COMPAT_SHARED_BLOCKS is your internal feature
> > that's not present in current upstream kernel AFAICS.
> 
> It isn't "my" feature; the value for
> EXT4_FEATURE_RO_COMPAT_SHARED_BLOCKS is defined in the headers in the
> e2fsprogs tree. The kernel currently does absolutely nothing with it,
> nor did it previously need to; it's just an RO_COMPAT feature which
> ensures that the kernel can only mount the filesystem read-only. The
> point is that an always-read-only filesystem will never change the block
> or inode bitmaps, so ensuring they don't overlap is unnecessary (and
> harmful).

Ah, I see. I missed EXT4_FEATURE_RO_COMPAT_SHARED_BLOCKS is actually
defined in e2fsprogs. Then what you suggests makes sense I guess and it's
good the headers are synced up again...

								Honza
-- 
Jan Kara <jack@suse.com>
SUSE Labs, CR

  reply	other threads:[~2020-10-05 16:19 UTC|newest]

Thread overview: 35+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-10-04 23:17 Linux 5.9-rc8 Linus Torvalds
2020-10-05  8:14 ` ext4 regression in v5.9-rc2 from e7bfb5c9bb3d on ro fs with overlapped bitmaps Josh Triplett
2020-10-05  9:46   ` Jan Kara
2020-10-05 10:16     ` Josh Triplett
2020-10-05 16:19       ` Jan Kara [this message]
2020-10-05 16:20   ` Jan Kara
2020-10-05 17:36   ` Darrick J. Wong
2020-10-06  0:04     ` Theodore Y. Ts'o
2020-10-06  0:32     ` Josh Triplett
2020-10-06  2:51       ` Darrick J. Wong
2020-10-06  3:18         ` Theodore Y. Ts'o
2020-10-06  5:03           ` Josh Triplett
2020-10-06  6:03             ` Josh Triplett
2020-10-06 13:35             ` Theodore Y. Ts'o
2020-10-07  8:03               ` Josh Triplett
2020-10-07 14:32                 ` Theodore Y. Ts'o
2020-10-07 20:14                   ` Josh Triplett
2020-10-08  2:10                     ` Theodore Y. Ts'o
2020-10-08 17:54                       ` Darrick J. Wong
2020-10-08 22:38                         ` Josh Triplett
2020-10-09  2:54                           ` Darrick J. Wong
2020-10-09 19:08                             ` Josh Triplett
2020-10-08 22:22                       ` Josh Triplett
2020-10-09 14:37                         ` Theodore Y. Ts'o
2020-10-09 20:30                           ` Josh Triplett
2021-01-10 18:41                           ` Malicious fs images was " Pavel Machek
2021-01-11 18:51                             ` Darrick J. Wong
2021-01-11 19:39                               ` Eric Biggers
2021-01-12 21:43                             ` Theodore Ts'o
2021-01-12 22:28                               ` Pavel Machek
2021-01-13  5:09                                 ` Theodore Ts'o
2020-10-08  2:57                     ` Andreas Dilger
2020-10-08 19:12                       ` Josh Triplett
2020-10-08 19:25                         ` Andreas Dilger
2020-10-08 22:28                           ` Josh Triplett

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