sync hangs - 2.6.35.10

[Jesper Krogh]

Hi.

I've just setup a 48 core server with 128GB of memory in a typical
HPC setup. The only IO-activity happens over NFS and the applications
are cpu-hogs.

The system is fully working and everthing looks apparently fine, but 
anything that
issue a sync is hung for eternity.

root fs is ext4 and it appears that sync hitting that drive get hung due
to some other things going on. There is only logging activity on that 
drive.

[  508.778695] Btrfs loaded
[ 7208.780233] INFO: task grub-probe:14787 blocked for more than 120 
seconds.
[ 7208.780316] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" 
disables this message.
[ 7208.780397] grub-probe    D 0000000000000000     0 14787  14768 
0x00000000
[ 7208.780402]  ffff882005f8fbb8 0000000000000086 ffff882000000000 
0000000000015880
[ 7208.780406]  ffff882005f8ffd8 0000000000015880 ffff882005f8ffd8 
ffff88200cd70000
[ 7208.780410]  0000000000015880 0000000000015880 ffff882005f8ffd8 
0000000000015880
[ 7208.780413] Call Trace:
[ 7208.780424]  [<ffffffff8155d3cd>] schedule_timeout+0x22d/0x310
[ 7208.780430]  [<ffffffff8102ccae>] ? physflat_send_IPI_mask+0xe/0x10
[ 7208.780433]  [<ffffffff8155c666>] wait_for_common+0xd6/0x180
[ 7208.780439]  [<ffffffff810533b0>] ? default_wake_function+0x0/0x20
[ 7208.780441]  [<ffffffff8155c7ed>] wait_for_completion+0x1d/0x20
[ 7208.780446]  [<ffffffff81160ff3>] writeback_inodes_sb+0xb3/0xe0
[ 7208.780449]  [<ffffffff81165c4e>] __sync_filesystem+0x4e/0xa0
[ 7208.780452]  [<ffffffff81165d7a>] sync_filesystem+0x3a/0x70
[ 7208.780456]  [<ffffffff8116f9fe>] fsync_bdev+0x2e/0x60
[ 7208.780460]  [<ffffffff8128e5ce>] blkdev_ioctl+0x4ee/0x820
[ 7208.780463]  [<ffffffff8116dfcc>] block_ioctl+0x3c/0x40
[ 7208.780468]  [<ffffffff8114edad>] vfs_ioctl+0x3d/0xd0
[ 7208.780471]  [<ffffffff8114f3b8>] do_vfs_ioctl+0x88/0x540
[ 7208.780475]  [<ffffffff811586fa>] ? alloc_fd+0x10a/0x150
[ 7208.780478]  [<ffffffff8114f8f1>] sys_ioctl+0x81/0xa0
[ 7208.780483]  [<ffffffff8100a032>] system_call_fastpath+0x16/0x1b

Full dmesg here: http://shrek.krogh.cc/~jesper/bonnie-dmesg.txt

It seems like the problems about broken sync writeback discussed
about a year ago .. last discussions in late january this year.

http://thread.gmane.org/gmane.linux.kernel/949268/focus=1090266

Any patches that may be relevant?

Thanks
--
Jesper
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