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SubjectRe: Deadlock on concurrent remount-ro and mdadm --stop (2.6.37)
On Fri, Jan 21, 2011 at 01:47:54PM +0100, Harald Braumann wrote:
> On shutdown `umountroot' and `mdadm-raid' are executed concurrently. The
> actual commands are:
> mount -o remount,ro /
> mdadm --stop --scan
>
> This seems to trigger a deadlock in the kernel. Dumping blocked tasks (sysrq-W)
> gives:
>
> md126_raid5: call trace:
> md_super_wait
> autoremove_wake_function
> bitmap_unplug
> ...
>
> mount: call trace:
> sync_page
> io_schedule
> sync_page

I've now disable parallel boot in my system, so umountroot and mdadm
shouldn't be called cuncurrently anymore. But I still get lock-ups on
mdadm --stop. Umountroot is called before mdadm --stop, and all other
filesystems are unmounted before that, so I guess
there should be no `sync_page' in progress anymore. But I also have
swap on the raid, so maybe there's a problem?

As not even the magic SysRQ keys work, I can't provide any more
details. Any suggestions how I could debug this problem?

Cheers,
harry


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