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Date:	Fri, 2 Apr 2010 13:01:25 +0200
From:	Pozsar Balazs <pozsy@...linux.hu>
To:	Michael Breuer <mbreuer@...jas.com>
Cc:	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: Hung task - sync - 2.6.33-rc7  w/md6 multicore rebuild in
	process


Hi all,

Was there any solution for this problem? We seem to be hitting the same 
problem with kernel 2.6.33.1, 12G RAM, and raid10. Noatime does not 
help.

Thanks
Balazs Pozsar




On Sat, Feb 13, 2010 at 11:51:10AM -0500, Michael Breuer wrote:
> 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>
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