Re: [Qemu-devel] [BUG] qemu-1.1.2 [FIXED-BY] qcow2: Fix avail_sectors in cluster allocation code

[Philipp Hahn <hahn@univention.de>]

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Hello Kevin,

Am Mittwoch 12 Dezember 2012 17:54:58 schrieb Kevin Wolf:
> Am 12.12.2012 15:09, schrieb Philipp Hahn:
> > Am Mittwoch 12 Dezember 2012 14:41:49 schrieb Kevin Wolf:
> >> As you can see in the commit message of that patch I was convinced that
> >> no bug did exist in practice and this was only dangerous with respect to
> >> future changes. Therefore my first question is if you're using an
> >> unmodified upstream qemu or if some backported patches are applied to
> >> it? If it's indeed unmodified, we should probably review the code once
> >> again to understand why it makes a difference.
> >
> > This were all unmodified versions directly from git between
> > "qemu-kvm-1.1.0" and "qemu-kvm-1.2.0"
> >
> > "git checkout b7ab0fea37c15ca9e249c42c46f5c48fd1a0943c" works,
> > "git checkout b7ab0fea37c15ca9e249c42c46f5c48fd1a0943c~1" is broken.
> > "git checkout qemu-kvm-1.1.2"  is broken,
> > "git checkout qemu-kvm-1.1.2 ; git cherry-pick
> > b7ab0fea37c15ca9e249c42c46f5c48fd1a0943c"  works
>
> Ok, thanks for clarifying. Then I must have missed some interesting case
> while doing the patch.

I just re-run my "git bisect run ~/bisect.sh"  case, but it again arrived at 
that patch. I just queued another run for tonight so make sure the test is 
reliable:

# bad: [4c3e02beed9878a5f760eeceb6cd42c475cf0127] Merge tag 'v1.2.0'
# good: [bd11ac4feb54d32653e5d4eb7994bed18be0609c] fdc: fix implied seek while 
there is no media in drive
git bisect start 'qemu-kvm-1.2.0' 'qemu-kvm-1.1.0'
# good: [15ecf28f39e2b6fba359ed094770c8fa4ad8dc60] Merge tag 'v1.1.0' into 
next
git bisect good 15ecf28f39e2b6fba359ed094770c8fa4ad8dc60
# bad: [2fa5008ffd49e51540756adccf966a2fcde6e6c1] hd-geometry: Factor out 
guess_chs_for_size()
git bisect bad 2fa5008ffd49e51540756adccf966a2fcde6e6c1
# bad: [306a571a2d75e32cd2eae5486c2714b7b7792a63] hw/arm_gic: Add qdev 
property for GIC revision
git bisect bad 306a571a2d75e32cd2eae5486c2714b7b7792a63
# good: [5c6f4f178ba542358c012ca033985f73e61b8ae5] z2: Rename PXA2xxState 
variable
git bisect good 5c6f4f178ba542358c012ca033985f73e61b8ae5
# good: [833e40858cb9501c5e76b3aa345e4bb5be34385a] qcow2: remove a line of 
unnecessary code
git bisect good 833e40858cb9501c5e76b3aa345e4bb5be34385a
# bad: [0b0cb9d310edfe2b2d108f18be4f013a1e552cfd] Merge remote-tracking 
branch 'kwolf/for-anthony' into staging
git bisect bad 0b0cb9d310edfe2b2d108f18be4f013a1e552cfd
# bad: [0446919dcab51e7468f346c0a009a88632c5c5e0] qemu-iotests: COW with many 
AIO requests on the same cluster
git bisect bad 0446919dcab51e7468f346c0a009a88632c5c5e0
# good: [b75a02829dde98723dfe16fa098338cb267b28b9] Prevent disk data loss when 
closing qemu
git bisect good b75a02829dde98723dfe16fa098338cb267b28b9
# good: [c4a248a138028bee63a099410c79b428db0c4779] block: copy 
enable_write_cache in bdrv_append
git bisect good c4a248a138028bee63a099410c79b428db0c4779
# good: [6af4e9ead4ec9491259c9861b1b35f9abee24a66] qcow2: always operate 
caches in writeback mode
git bisect good 6af4e9ead4ec9491259c9861b1b35f9abee24a66
# bad: [b7ab0fea37c15ca9e249c42c46f5c48fd1a0943c] qcow2: Fix avail_sectors in 
cluster allocation code
git bisect bad b7ab0fea37c15ca9e249c42c46f5c48fd1a0943c
# good: [cdba7fee1daa8865bac2d69da288171fe7c21aae] qcow2: Simplify calculation 
for COW area at the end
git bisect good cdba7fee1daa8865bac2d69da288171fe7c21aae

> Ideally we would find a sequence of qemu-io commands to reliably
> reproduce this. First thing worth trying would be running the current
> qemu-iotests suite on the old versions. If we don't find it this way, I
> guess we need to catch it with code review. I'm not sure if I can get to
> it this week, and starting next week I'll be on vacation, so any help
> with finding a reproducer would be appreciated.

I'll have a look at it tommorrow.

Thank you for your fast replies and have a nice vacation in case we don't head 
from each other this week again.

BYtE
Philipp
-- 
Philipp Hahn           Open Source Software Engineer      hahn@univention.de
Univention GmbH        be open.                       fon: +49 421 22 232- 0
Mary-Somerville-Str.1  D-28359 Bremen                 fax: +49 421 22 232-99
                                                   http://www.univention.de/

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