Bug 607245 - snapshot of root lv hangs
snapshot of root lv hangs
Status: CLOSED RAWHIDE
Product: Fedora
Classification: Fedora
Component: kernel (Show other bugs)
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low Severity medium
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Assigned To: Eric Sandeen
Fedora Extras Quality Assurance
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Reported: 2010-06-23 11:41 EDT by Zing
Modified: 2010-07-01 16:48 EDT (History)
18 users (show)

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Fixed In Version: kernel-2.6.35-0.15.rc3.git3
Doc Type: Bug Fix
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Last Closed: 2010-07-01 16:48:23 EDT
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Description Zing 2010-06-23 11:41:49 EDT
Description of problem:
when I try to snapshot my root lv it hangs here:

==========================================================================
[root@RAWHIDE ~]# lvcreate -v -s -n snaproot -L 100M /dev/mainvg/rootlv
    Setting chunksize to 8 sectors.
    Setting logging type to disk
    Finding volume group "mainvg"
    Archiving volume group "mainvg" metadata (seqno 114).
    Creating logical volume snaproot
    Creating volume group backup "/etc/lvm/backup/mainvg" (seqno 115).
    Found volume group "mainvg"
    Creating mainvg-snaproot
    Loading mainvg-snaproot table (253:2)
    Resuming mainvg-snaproot (253:2)
    Clearing start of logical volume "snaproot"
    Creating logical volume snapshot0
    Found volume group "mainvg"
    Found volume group "mainvg"
    Creating mainvg-rootlv-real
    Loading mainvg-rootlv-real table (253:3)
    Resuming mainvg-rootlv-real (253:3)
    Loading mainvg-rootlv table (253:0)
    Creating mainvg-snaproot-cow
    Loading mainvg-snaproot-cow table (253:4)
    Resuming mainvg-snaproot-cow (253:4)
    Loading mainvg-snaproot table (253:2)
    Suspending mainvg-rootlv (253:0) with filesystem sync with device flush
=========================================================================

I/O on the system is then blocked and reboot needed.

lv's other than the root lv I can successfully snapshot.

Version-Release number of selected component (if applicable):
kernel-2.6.35-0.2.rc3.git0.fc14.x86_64
lvm2-2.02.67-1.fc14.x86_64
device-mapper-1.02.49-1.fc14.x86_64

Additional info:
If I revert back to kernel-2.6.34-20.fc14.x86_64, snapshots of my root lv are successful again.

This install is running in a qemu-kvm if that matters.
Comment 1 Milan Broz 2010-06-23 11:57:05 EDT
This is probably problem described here
https://www.redhat.com/archives/dm-devel/2010-June/msg00084.html

Reassigning to kernel, according the thread, reverting 6b0310fbf087ad6 fixes the problem.
Comment 2 Eric Sandeen 2010-06-23 12:01:05 EDT
Yeah, this one's mine.

It doesn't have to be the root, I think, any volume w/ active IO may hit this, sadly.
Comment 3 Eric Sandeen 2010-06-23 16:45:20 EDT
I sent a patch upstream (linux-fsdevel & linux-ext4) for this, there seem to be other deadlocks lurking but this should fix up the egregious one I introduced.

[PATCH] ext4: fix freeze deadlock under IO

I'll toss it into rawhide for testing.
Comment 4 Eric Sandeen 2010-07-01 16:48:23 EDT
s/b fixed in 2.6.35-0.15.rc3.git3

pls test & re-open if you still have trouble.

Thanks,
-Eric

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