Re: nfsd loads 90% CPU, client hangs

[J. Bruce Fields]

On Fri, Jun 05, 2009 at 08:27:54AM +0400, Sergey Lapin wrote:
> Hi, all!
> 
> With recent kernels I see a problem with using NFS. It was broken
> somewhere after 2.6.27.

In other words, it worked in 2.6.27?  So the regression is somewhere
between 2.6.27 and 2.6.30-rc8?

Can you figure out what the running nfsd threads are doing?

--b.

> 
> I have ARM board with several hard drives connected over USB 1.1
> dongles (USB->IDE, USB->SATA). And I have lvm2 over them.
> They produce 2 logical volumes with data, which are exported
> over NFS to PC host. ARM box runs vanilla kernel 2.6.30-rc8,
> and PC host runs Debian kernel 2.6.24. After some bigger file writes
> (when large amounts of data are written to disks) I experience the
> following error in logs on ARM nfsd server host. I use kernel nfsd here,
> to be clear. I use NFSv3.
> 
> INFO: task nfsd:1933 blocked for more than 120 seconds.
> "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this
> message.
> nfsd          D c02e29e8     0  1933      2
> [<c02e29e8>] (__schedule+0x2d8/0x348) from [<c02e374c>]
> (__mutex_lock_slowpath+0x8c/0xfc)
> [<c02e374c>] (__mutex_lock_slowpath+0x8c/0xfc) from [<c006d670>]
> (generic_file_aio_write+0x58/0xe8)
> [<c006d670>] (generic_file_aio_write+0x58/0xe8) from [<c00dc1ec>]
> (ext3_file_write+0x20/0xa0)
> [<c00dc1ec>] (ext3_file_write+0x20/0xa0) from [<c0093cc8>]
> (do_sync_readv_writev+0xac/0x100)
> [<c0093cc8>] (do_sync_readv_writev+0xac/0x100) from [<c00943e4>]
> (do_readv_writev+0xac/0x1b0)
> [<c00943e4>] (do_readv_writev+0xac/0x1b0) from [<c009454c>]
> (vfs_writev+0x64/0x74)
> [<c009454c>] (vfs_writev+0x64/0x74) from [<c0124c88>]
> (nfsd_vfs_write+0x10c/0x350)
> [<c0124c88>] (nfsd_vfs_write+0x10c/0x350) from [<c01257b4>]
> (nfsd_write+0xc0/0xd8)
> [<c01257b4>] (nfsd_write+0xc0/0xd8) from [<c012c354>]
> (nfsd3_proc_write+0xe8/0x114)
> [<c012c354>] (nfsd3_proc_write+0xe8/0x114) from [<c0120f90>]
> (nfsd_dispatch+0xcc/0x1e4)
> [<c0120f90>] (nfsd_dispatch+0xcc/0x1e4) from [<c02d3f34>]
> (svc_process+0x42c/0x7a8)
> [<c02d3f34>] (svc_process+0x42c/0x7a8) from [<c0121640>]
> (nfsd+0xe4/0x148)
> [<c0121640>] (nfsd+0xe4/0x148) from [<c0056720>] (kthread+0x58/0x90)
> [<c0056720>] (kthread+0x58/0x90) from [<c0044e90>] (do_exit+0x0/0x620)
> [<c0044e90>] (do_exit+0x0/0x620) from [<ffffffff>] (0xffffffff)
> 
> And then NFS doesn't work at all with nfsd consuming all of CPU it can.
> I see no hardware problems here, because files are perfectly accessible
> locally or over HTTP, and no USB or disk error messages.
> 
> If I reboot ARM box without unmounting NFS shares on PC, the same
> situation occurs as soon as ARM box boots (excessively loaded CPU with
> nfsd at top, and NFS doesn't work and doesn't recover). If I unmount
> them, box boots fine, but fails again as soon as I repeat file
> operation.
> So, the question is - what causes it and if it is possible to fix this
> problem or work it around?
> 
> Thanks a lot,
> S.
> 
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