Scenario:
1. raid6 (software - 6 1Tb sata drives) doing a resync (multi core enabled)
2. rebuilding kernel (rc8)
3. system became sluggish - top & vmstat showed all 12Gb ram used -
albeit 10g of fs cache. It seemed as though relcaim of fs cache became
really slow once there were no more "free" pages.
vmstat <after hung task reported - don't have from before>
procs -----------memory---------- ---swap-- -----io---- --system--
-----cpu-----
r b swpd free buff cache si so bi bo in cs us sy
id wa st
0 1 808 112476 347592 9556952 0 0 39 388 158 189 1
18 77 4 0
4. Worrying a bit about the looming instability, I typed, "sync."
5. sync took a long time, and was reported by the kernel as a hung task
(repeatedly) - see below.
6. entering additional sync commands also hang (unsuprising, but figured
I'd try as non-root).
7. The running sync (pid 11975) cannot be killed.
8. echo 1 > drop_caches does clear the fs cache. System behaves better
after this (but sync is still hung).
config attached.
Running with sky2 dma patches (in rc8) and increased the audit name
space to avoid the flood of name space maxed warnings.
My current plan is to let the raid rebuild complete and then reboot (to
rc8 if the bits made it to disk)... maybe with a backup of recently
changed files to an external system.
Feb 13 10:54:13 mail kernel: INFO: task sync:11975 blocked for more than
120 seconds.
Feb 13 10:54:13 mail kernel: "echo 0 >
/proc/sys/kernel/hung_task_timeout_secs" disables this message.
Feb 13 10:54:13 mail kernel: sync D 0000000000000002 0
11975 6433 0x00000000
Feb 13 10:54:13 mail kernel: ffff8801c45f3da8 0000000000000082
ffff8800282f5948 ffff8800282f5920
Feb 13 10:54:13 mail kernel: ffff88032f785d78 ffff88032f785d40
000000030c37a771 0000000000000282
Feb 13 10:54:13 mail kernel: ffff8801c45f3fd8 000000000000f888
ffff88032ca00000 ffff8801c61c9750
Feb 13 10:54:13 mail kernel: Call Trace:
Feb 13 10:54:13 mail kernel: [<ffffffff81154730>] ? bdi_sched_wait+0x0/0x20
Feb 13 10:54:13 mail kernel: [<ffffffff8115473e>] bdi_sched_wait+0xe/0x20
Feb 13 10:54:13 mail kernel: [<ffffffff81537b4f>] __wait_on_bit+0x5f/0x90
Feb 13 10:54:13 mail kernel: [<ffffffff81154730>] ? bdi_sched_wait+0x0/0x20
Feb 13 10:54:13 mail kernel: [<ffffffff81537bf8>]
out_of_line_wait_on_bit+0x78/0x90
Feb 13 10:54:13 mail kernel: [<ffffffff81078650>] ?
wake_bit_function+0x0/0x50
Feb 13 10:54:13 mail kernel: [<ffffffff8104ac55>] ?
wake_up_process+0x15/0x20
Feb 13 10:54:13 mail kernel: [<ffffffff81155daf>]
bdi_sync_writeback+0x6f/0x80
Feb 13 10:54:13 mail kernel: [<ffffffff81155de2>] sync_inodes_sb+0x22/0x100
Feb 13 10:54:13 mail kernel: [<ffffffff81159902>]
__sync_filesystem+0x82/0x90
Feb 13 10:54:13 mail kernel: [<ffffffff81159a04>]
sync_filesystems+0xf4/0x120
Feb 13 10:54:13 mail kernel: [<ffffffff81159a91>] sys_sync+0x21/0x40
Feb 13 10:54:13 mail kernel: [<ffffffff8100b0f2>]
system_call_fastpath+0x16/0x1b
<this repeats every 120 seconds - all the same traceback>