I'm running
Linux io 2.6.32-23-server #37-Ubuntu SMP Fri Jun 11 09:11:11 UTC 2010 x86_64 GNU/Linux
with all upgrades installed and I got a freeze today. Since this is a multi-user file server I'm not sure what exactly was going on at the time. Unfortunately, I cannot try out different kernels either as the machine is always in use.

Jul  7 11:29:57 io kernel: [254640.440019] INFO: task jbd2/sdb-8:942 blocked for more than 120 seconds.
Jul  7 11:29:57 io kernel: [254640.440033] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
Jul  7 11:29:57 io kernel: [254640.440042] jbd2/sdb-8    D 00000000ffffffff     0   942      2 0x00000000
Jul  7 11:29:57 io kernel: [254640.440047]  ffff88007bd71d20 0000000000000046 0000000000015bc0 0000000000015bc0
Jul  7 11:29:57 io kernel: [254640.440052]  ffff88007bff9ab0 ffff88007bd71fd8 0000000000015bc0 ffff88007bff96f0
Jul  7 11:29:57 io kernel: [254640.440056]  0000000000015bc0 ffff88007bd71fd8 0000000000015bc0 ffff88007bff9ab0
Jul  7 11:29:57 io kernel: [254640.440060] Call Trace:
Jul  7 11:29:57 io kernel: [254640.440069]  [<ffffffff8121b9a1>] jbd2_journal_commit_transaction+0x1c1/0x1250
Jul  7 11:29:57 io kernel: [254640.440075]  [<ffffffff81076c7c>] ? lock_timer_base+0x3c/0x70
Jul  7 11:29:57 io kernel: [254640.440080]  [<ffffffff81085090>] ? autoremove_wake_function+0x0/0x40
Jul  7 11:29:57 io kernel: [254640.440084]  [<ffffffff81222f6d>] kjournald2+0xbd/0x220
Jul  7 11:29:57 io kernel: [254640.440088]  [<ffffffff81085090>] ? autoremove_wake_function+0x0/0x40
Jul  7 11:29:57 io kernel: [254640.440091]  [<ffffffff81222eb0>] ? kjournald2+0x0/0x220
Jul  7 11:29:57 io kernel: [254640.440094]  [<ffffffff81084d16>] kthread+0x96/0xa0
Jul  7 11:29:57 io kernel: [254640.440099]  [<ffffffff810141ea>] child_rip+0xa/0x20
Jul  7 11:29:57 io kernel: [254640.440102]  [<ffffffff81084c80>] ? kthread+0x0/0xa0
Jul  7 11:29:57 io kernel: [254640.440105]  [<ffffffff810141e0>] ? child_rip+0x0/0x20
Jul  7 11:29:57 io kernel: [254640.440113] INFO: task nfsd:1753 blocked for more than 120 seconds.
Jul  7 11:29:57 io kernel: [254640.440119] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
Jul  7 11:29:57 io kernel: [254640.440126] nfsd          D 0000000000000000     0  1753      2 0x00000000
Jul  7 11:29:57 io kernel: [254640.440130]  ffff88007b345b10 0000000000000046 0000000000015bc0 0000000000015bc0
Jul  7 11:29:57 io kernel: [254640.440135]  ffff88007cbc4890 ffff88007b345fd8 0000000000015bc0 ffff88007cbc44d0
Jul  7 11:29:57 io kernel: [254640.440139]  0000000000015bc0 ffff88007b345fd8 0000000000015bc0 ffff88007cbc4890
Jul  7 11:29:57 io kernel: [254640.440143] Call Trace:
Jul  7 11:29:57 io kernel: [254640.440147]  [<ffffffff81219ce1>] start_this_handle+0x251/0x4b0
Jul  7 11:29:57 io kernel: [254640.440150]  [<ffffffff81085090>] ? autoremove_wake_function+0x0/0x40
Jul  7 11:29:57 io kernel: [254640.440154]  [<ffffffff81559cde>] ? _spin_lock+0xe/0x20
Jul  7 11:29:57 io kernel: [254640.440158]  [<ffffffff8121a115>] jbd2_journal_start+0xb5/0x100
Jul  7 11:29:57 io kernel: [254640.440162]  [<ffffffff811f80b8>] ext4_journal_start_sb+0x58/0x90
Jul  7 11:29:57 io kernel: [254640.440167]  [<ffffffff811deb9a>] ext4_dirty_inode+0x2a/0x60
Jul  7 11:29:57 io kernel: [254640.440171]  [<ffffffff81166f12>] __mark_inode_dirty+0x42/0x1e0
Jul  7 11:29:57 io kernel: [254640.440174]  [<ffffffff8115d29c>] inode_setattr+0x7c/0x170
Jul  7 11:29:57 io kernel: [254640.440178]  [<ffffffff811ded56>] ext4_setattr+0x186/0x370
Jul  7 11:29:57 io kernel: [254640.440181]  [<ffffffff8115d4fb>] notify_change+0x16b/0x350
Jul  7 11:29:57 io kernel: [254640.440196]  [<ffffffffa031d440>] nfsd_setattr+0x330/0x460 [nfsd]
Jul  7 11:29:57 io kernel: [254640.440205]  [<ffffffffa0327a26>] nfsd3_proc_setattr+0x76/0xc0 [nfsd]
Jul  7 11:29:57 io kernel: [254640.440213]  [<ffffffffa031844e>] nfsd_dispatch+0xfe/0x250 [nfsd]
Jul  7 11:29:57 io kernel: [254640.440230]  [<ffffffffa0129664>] svc_process_common+0x344/0x610 [sunrpc]
Jul  7 11:29:57 io kernel: [254640.440235]  [<ffffffff8105b210>] ? default_wake_function+0x0/0x20
Jul  7 11:29:57 io kernel: [254640.440247]  [<ffffffffa0129a40>] svc_process+0x110/0x150 [sunrpc]
Jul  7 11:29:57 io kernel: [254640.440254]  [<ffffffffa0318af5>] nfsd+0xc5/0x170 [nfsd]
Jul  7 11:29:57 io kernel: [254640.440261]  [<ffffffffa0318a30>] ? nfsd+0x0/0x170 [nfsd]
Jul  7 11:29:57 io kernel: [254640.440264]  [<ffffffff81084d16>] kthread+0x96/0xa0
Jul  7 11:29:57 io kernel: [254640.440268]  [<ffffffff810141ea>] child_rip+0xa/0x20
Jul  7 11:29:57 io kernel: [254640.440271]  [<ffffffff81084c80>] ? kthread+0x0/0xa0
Jul  7 11:29:57 io kernel: [254640.440274]  [<ffffffff810141e0>] ? child_rip+0x0/0x20
Jul  7 11:29:57 io kernel: [254640.440277] INFO: task nfsd:1755 blocked for more than 120 seconds.
Jul  7 11:29:57 io kernel: [254640.440283] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
Jul  7 11:29:57 io kernel: [254640.440290] nfsd          D 0000000000000003     0  1755      2 0x00000000
Jul  7 11:29:57 io kernel: [254640.440294]  ffff8800365ffb90 0000000000000046 0000000000015bc0 0000000000015bc0
Jul  7 11:29:57 io kernel: [254640.440298]  ffff88007ade03c0 ffff8800365fffd8 0000000000015bc0 ffff88007ade0000
Jul  7 11:29:57 io kernel: [254640.440302]  0000000000015bc0 ffff8800365fffd8 0000000000015bc0 ffff88007ade03c0
Jul  7 11:29:57 io kernel: [254640.440307] Call Trace:
Jul  7 11:29:57 io kernel: [254640.440310]  [<ffffffff81219ce1>] start_this_handle+0x251/0x4b0
Jul  7 11:29:57 io kernel: [254640.440314]  [<ffffffff81085090>] ? autoremove_wake_function+0x0/0x40
Jul  7 11:29:57 io kernel: [254640.440318]  [<ffffffff8121a115>] jbd2_journal_start+0xb5/0x100
Jul  7 11:29:57 io kernel: [254640.440321]  [<ffffffff811f80b8>] ext4_journal_start_sb+0x58/0x90
Jul  7 11:29:57 io kernel: [254640.440325]  [<ffffffff811dedf0>] ext4_setattr+0x220/0x370
Jul  7 11:29:57 io kernel: [254640.440328]  [<ffffffff8115d4fb>] notify_change+0x16b/0x350
Jul  7 11:29:57 io kernel: [254640.440337]  [<ffffffffa031d440>] nfsd_setattr+0x330/0x460 [nfsd]
Jul  7 11:29:57 io kernel: [254640.440345]  [<ffffffffa0327a26>] nfsd3_proc_setattr+0x76/0xc0 [nfsd]
Jul  7 11:29:57 io kernel: [254640.440353]  [<ffffffffa031844e>] nfsd_dispatch+0xfe/0x250 [nfsd]
Jul  7 11:29:57 io kernel: [254640.440364]  [<ffffffffa0129664>] svc_process_common+0x344/0x610 [sunrpc]
Jul  7 11:29:57 io kernel: [254640.440369]  [<ffffffff8105b210>] ? default_wake_function+0x0/0x20
Jul  7 11:29:57 io kernel: [254640.440380]  [<ffffffffa0129a40>] svc_process+0x110/0x150 [sunrpc]
Jul  7 11:29:57 io kernel: [254640.440387]  [<ffffffffa0318af5>] nfsd+0xc5/0x170 [nfsd]
Jul  7 11:29:57 io kernel: [254640.440394]  [<ffffffffa0318a30>] ? nfsd+0x0/0x170 [nfsd]
Jul  7 11:29:57 io kernel: [254640.440398]  [<ffffffff81084d16>] kthread+0x96/0xa0
Jul  7 11:29:57 io kernel: [254640.440401]  [<ffffffff810141ea>] child_rip+0xa/0x20
Jul  7 11:29:57 io kernel: [254640.440404]  [<ffffffff81084c80>] ? kthread+0x0/0xa0
Jul  7 11:29:57 io kernel: [254640.440407]  [<ffffffff810141e0>] ? child_rip+0x0/0x20
Jul  7 11:29:57 io kernel: [254640.440410] INFO: task nfsd:1757 blocked for more than 120 seconds.
Jul  7 11:29:57 io kernel: [254640.440416] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
Jul  7 11:29:57 io kernel: [254640.440423] nfsd          D 0000000000000002     0  1757      2 0x00000000
Jul  7 11:29:57 io kernel: [254640.440427]  ffff880036b03b10 0000000000000046 0000000000015bc0 0000000000015bc0
Jul  7 11:29:57 io kernel: [254640.440431]  ffff88007b254890 ffff880036b03fd8 0000000000015bc0 ffff88007b2544d0
Jul  7 11:29:57 io kernel: [254640.440435]  0000000000015bc0 ffff880036b03fd8 0000000000015bc0 ffff88007b254890
Jul  7 11:29:57 io kernel: [254640.440439] Call Trace:
Jul  7 11:29:57 io kernel: [254640.440443]  [<ffffffff81219ce1>] start_this_handle+0x251/0x4b0
Jul  7 11:29:57 io kernel: [254640.440447]  [<ffffffff81085090>] ? autoremove_wake_function+0x0/0x40
Jul  7 11:29:57 io kernel: [254640.440451]  [<ffffffff8121a115>] jbd2_journal_start+0xb5/0x100
Jul  7 11:29:57 io kernel: [254640.440455]  [<ffffffff8127e8e1>] ? aa_alloc_task_context+0x31/0xa0
Jul  7 11:29:57 io kernel: [254640.440459]  [<ffffffff811f80b8>] ext4_journal_start_sb+0x58/0x90
Jul  7 11:29:57 io kernel: [254640.440463]  [<ffffffff811deb9a>] ext4_dirty_inode+0x2a/0x60
Jul  7 11:29:57 io kernel: [254640.440466]  [<ffffffff81166f12>] __mark_inode_dirty+0x42/0x1e0
Jul  7 11:29:57 io kernel: [254640.440469]  [<ffffffff8115d29c>] inode_setattr+0x7c/0x170
Jul  7 11:29:57 io kernel: [254640.440473]  [<ffffffff811ded56>] ext4_setattr+0x186/0x370
Jul  7 11:29:57 io kernel: [254640.440476]  [<ffffffff8115d4fb>] notify_change+0x16b/0x350
Jul  7 11:29:57 io kernel: [254640.440484]  [<ffffffffa031d440>] nfsd_setattr+0x330/0x460 [nfsd]
Jul  7 11:29:57 io kernel: [254640.440493]  [<ffffffffa0327a26>] nfsd3_proc_setattr+0x76/0xc0 [nfsd]
Jul  7 11:29:57 io kernel: [254640.440500]  [<ffffffffa031844e>] nfsd_dispatch+0xfe/0x250 [nfsd]
Jul  7 11:29:57 io kernel: [254640.440512]  [<ffffffffa0129664>] svc_process_common+0x344/0x610 [sunrpc]
Jul  7 11:29:57 io kernel: [254640.440516]  [<ffffffff8105b210>] ? default_wake_function+0x0/0x20
Jul  7 11:29:57 io kernel: [254640.440528]  [<ffffffffa0129a40>] svc_process+0x110/0x150 [sunrpc]
Jul  7 11:29:57 io kernel: [254640.440535]  [<ffffffffa0318af5>] nfsd+0xc5/0x170 [nfsd]
Jul  7 11:29:57 io kernel: [254640.440542]  [<ffffffffa0318a30>] ? nfsd+0x0/0x170 [nfsd]
Jul  7 11:29:57 io kernel: [254640.440545]  [<ffffffff81084d16>] kthread+0x96/0xa0
Jul  7 11:29:57 io kernel: [254640.440549]  [<ffffffff810141ea>] child_rip+0xa/0x20
Jul  7 11:29:57 io kernel: [254640.440552]  [<ffffffff81084c80>] ? kthread+0x0/0xa0
Jul  7 11:29:57 io kernel: [254640.440555]  [<ffffffff810141e0>] ? child_rip+0x0/0x20

dmesg attached