On 05/23/2010 01:10 AM, Jim Paris wrote:
Antoine Martin wrote:
On 02/27/2010 12:38 AM, Antoine Martin wrote:
1 0 0 98 0 1| 0 0 | 66B 354B| 0 0 | 30 11
1 1 0 98 0 0| 0 0 | 66B 354B| 0 0 | 29 11
> From that point onwards, nothing will happen.
The host has disk IO to spare... So what is it waiting for??
Moved to an AMD64 host. No effect.
Disabled swap before running the test. No effect.
Moved the guest to a fully up-to-date FC12 server
(2.6.31.6-145.fc12.x86_64), no effect.
I have narrowed it down to the guest's filesystem used for backing
the disk image which is loop mounted: although it was not
completely full (and had enough inodes), freeing some space on it
prevents the system from misbehaving.
FYI: the disk image was clean and was fscked before each test. kvm
had been updated to 0.12.3
The weird thing is that the same filesystem works fine (no system
hang) if used directly from the host, it is only misbehaving via
kvm...
So I am not dismissing the possibility that kvm may be at least
partly to blame, or that it is exposing a filesystem bug (race?)
not normally encountered.
(I have backed up the full 32GB virtual disk in case someone
suggests further investigation)
Well, well. I've just hit the exact same bug on another *host* (not
a guest), running stock Fedora 12.
So this isn't a kvm bug after all. Definitely a loop+ext(4?) bug.
Looks like you need a pretty big loop mounted partition to trigger
it. (bigger than available ram?)
This is what triggered it on a quad amd system with 8Gb of ram,
software raid-1 partition:
mount -o loop 2GB.dd source
dd if=/dev/zero of=8GB.dd bs=1048576 count=8192
mkfs.ext4 -f 8GB.dd
mount -o loop 8GB.dd dest
rsync -rplogtD source/* dest/
umount source
umount dest
^ this is where it hangs, I then tried to issue a 'sync' from
another terminal, which also hung.
It took more than 10 minutes to settle itself, during that time one
CPU was stuck in wait state.
This sounds like:
https://bugzilla.kernel.org/show_bug.cgi?id=15906
https://bugzilla.redhat.com/show_bug.cgi?id=588930
Indeed it does.
Let's hope this makes it to -stable fast.
Antoine
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