From: "Darrick J. Wong" <darrick.wong@oracle.com>
To: TR Reardon <thomas_reardon@hotmail.com>
Cc: "linux-ext4@vger.kernel.org" <linux-ext4@vger.kernel.org>
Subject: Re: tune2fs -O ^metadata_csum not checking bitmap failures
Date: Wed, 10 Sep 2014 14:16:36 -0700 [thread overview]
Message-ID: <20140910211636.GI10351@birch.djwong.org> (raw)
In-Reply-To: <BAY179-W439AA99AF43810A0FC1C49FDCF0@phx.gbl>
On Wed, Sep 10, 2014 at 05:10:21PM -0400, TR Reardon wrote:
> > Date: Wed, 10 Sep 2014 13:48:40 -0700
> > From: darrick.wong@oracle.com
> > To: thomas_reardon@hotmail.com
> > CC: linux-ext4@vger.kernel.org
> > Subject: Re: tune2fs -O ^metadata_csum not checking bitmap failures
> >
> > On Wed, Sep 10, 2014 at 04:30:41PM -0400, TR Reardon wrote:
> >> When running tune2fs -O ^metadata_csum, disable_uninit_bg() is called to
> >> reset the gdt. However, return value is not checked, which allows a failure
> >> (say, a block bitmap failure somewhere, among other errors) to continue
> >> through to rewrite_metadata_checksums()
> >>
> >> This seems wrong; should not the rewrite occur only if
> >> disable/enable_uninit_bg() succeeds?
> >
> > The rewrite will fail if either of the error cases in disable_uninit_bg() fail,
> > since rewrite_metadata_checksums() also tries to load the bitmap and scan the
> > inodes.
>
> Actually, rewrite_metadata_checksums() loads the bitmap with checksums OFF,
> which in the test I just ran, will succeed. This leaves the fs in a weird
> half-checksummed state.
Icky. :(
> I should have been clearer above: if the initial disable_uninit_bg() failure
> occurs because of a *checksum error*, then we get into this confused state.
> Given that people would possibly try to disable metadata_csum if there are
> checksum errors, this seems like a fairly common scenario.
I would say that if you have checksum errors you ought to run e2fsck, not just
tape over the warning light...
...though if you're prepared to deal with the fallout/really know what you're
doing, you can nuke the feature bit with 'feature ^metadata_csum' in debugfs.
In any case, we ought to avoid tune2fs writing junk to a broken fs.
--D
>
>
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prev parent reply other threads:[~2014-09-10 21:16 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-09-10 20:30 tune2fs -O ^metadata_csum not checking bitmap failures TR Reardon
2014-09-10 20:48 ` Darrick J. Wong
2014-09-10 21:10 ` TR Reardon
2014-09-10 21:16 ` Darrick J. Wong [this message]
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