linux-kernel - Re: autofs4 hang in 2.6.37-rc1

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Message-Id: <201011141615.32166.arnd@arndb.de>
Date:	Sun, 14 Nov 2010 16:15:32 +0100
From:	Arnd Bergmann <arnd@...db.de>
To:	Avi Kivity <avi@...hat.com>
Cc:	Ian Kent <raven@...maw.net>, autofs@...ux.kernel.org,
	"linux-kernel" <linux-kernel@...r.kernel.org>
Subject: Re: autofs4 hang in 2.6.37-rc1

On Sunday 14 November 2010 14:51:04 Avi Kivity wrote:
> automount     S ffff88012a28a680     0   399      1 0x00000000
>   ffff88012a07bd08 0000000000000082 0000000000000000 0000000000000000
>   ffff88012a07a010 ffff88012a07bfd8 0000000000011800 ffff88012693c260
>   ffff88012693c5d0 ffff88012693c5c8 0000000000011800 0000000000011800
> Call Trace:
>   [<ffffffff81056197>] ? prepare_to_wait+0x67/0x74
>   [<ffffffff811b23eb>] autofs4_wait+0x5a4/0x6d5
>   [<ffffffff81055f25>] ? autoremove_wake_function+0x0/0x34
>   [<ffffffff811b2ba5>] autofs4_do_expire_multi+0x5b/0xa3
>   [<ffffffff811b2c39>] autofs4_expire_multi+0x4c/0x54
>   [<ffffffff811b1750>] autofs4_root_ioctl_unlocked+0x23e/0x252
>   [<ffffffff811b1808>] autofs4_root_ioctl+0x39/0x53
>   [<ffffffff810f5e5c>] do_vfs_ioctl+0x557/0x5bb
>   [<ffffffff810ca644>] ? remove_vma+0x6e/0x76
>   [<ffffffff810cb6a2>] ? do_munmap+0x31c/0x33e
>   [<ffffffff810f5f02>] sys_ioctl+0x42/0x65
>   [<ffffffff81002b42>] system_call_fastpath+0x16/0x1b
> 
> 
> Shouldn't we drop autofs4_ioctl_mutex while we wait?

If the ioctl can sleep for multiple seconds, the mutex should
indeed be dropped, and that would be safe because we used to
do the same with the BKL.

The question is why this would sleep for more than 120 seconds.

	Arnd
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