[Bug 561210] Re: Writing big files to NFS target causes system lock up

[David McBride]

And, indeed, if the umount process is stuck for long enough, the
following kernel stack-trace is emitted:

Jul 26 21:38:49 illustrious kernel: [  838.729063] INFO: task umount.nfs:2570 blocked for more than 120 seconds.
Jul 26 21:38:49 illustrious kernel: [  838.729069] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
Jul 26 21:38:49 illustrious kernel: [  838.729073] umount.nfs    D 0000000000000000     0  2570      1 0x00000000
Jul 26 21:38:49 illustrious kernel: [  838.729080]  ffff8801d5747d98 0000000000000086 0000000000015bc0 0000000000015bc0
Jul 26 21:38:49 illustrious kernel: [  838.729087]  ffff880210ec03c0 ffff8801d5747fd8 0000000000015bc0 ffff880210ec0000
Jul 26 21:38:49 illustrious kernel: [  838.729092]  0000000000015bc0 ffff8801d5747fd8 0000000000015bc0 ffff880210ec03c0
Jul 26 21:38:49 illustrious kernel: [  838.729098] Call Trace:
Jul 26 21:38:49 illustrious kernel: [  838.729110]  [<ffffffff811650d0>] ? bdi_sched_wait+0x0/0x20
Jul 26 21:38:49 illustrious kernel: [  838.729115]  [<ffffffff811650de>] bdi_sched_wait+0xe/0x20
Jul 26 21:38:49 illustrious kernel: [  838.729123]  [<ffffffff8153f3af>] __wait_on_bit+0x5f/0x90
Jul 26 21:38:49 illustrious kernel: [  838.729127]  [<ffffffff811650d0>] ? bdi_sched_wait+0x0/0x20
Jul 26 21:38:49 illustrious kernel: [  838.729132]  [<ffffffff8153f458>] out_of_line_wait_on_bit+0x78/0x90
Jul 26 21:38:49 illustrious kernel: [  838.729140]  [<ffffffff81085360>] ? wake_bit_function+0x0/0x40
Jul 26 21:38:49 illustrious kernel: [  838.729144]  [<ffffffff81165094>] ? bdi_queue_work+0xa4/0xe0
Jul 26 21:38:49 illustrious kernel: [  838.729149]  [<ffffffff8116640f>] bdi_sync_writeback+0x6f/0x80
Jul 26 21:38:49 illustrious kernel: [  838.729154]  [<ffffffff81166440>] sync_inodes_sb+0x20/0x30
Jul 26 21:38:49 illustrious kernel: [  838.729160]  [<ffffffff81169f12>] __sync_filesystem+0x82/0x90
Jul 26 21:38:49 illustrious kernel: [  838.729164]  [<ffffffff81169ff9>] sync_filesystems+0xd9/0x130
Jul 26 21:38:49 illustrious kernel: [  838.729171]  [<ffffffff8115ece1>] sys_umount+0xb1/0xd0
Jul 26 21:38:49 illustrious kernel: [  838.729178]  [<ffffffff810131b2>] system_call_fastpath+0x16/0x1b

I've also identified that my test NFS mount was using UDP, and performs
several times *better* in terms of IO throughput when switched to TCP
operation.  This lack of performance (and responsiveness) may have been
masking some other issues, so I'll use TCP for future testing.

-- 
Writing big files to NFS target causes system lock up
https://bugs.launchpad.net/bugs/561210
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