linux-kernel - Re: mount -o loop with truncated dosdisk.img uses 100% cpu and can't be killed

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Date:	Thu, 12 Jul 2012 10:16:46 -0500
From:	"Steven J. Magnani" <steve@...idescorp.com>
To:	Stevie Trujillo <stevie.trujillo@...il.com>
Cc:	OGAWA Hirofumi <hirofumi@...l.parknet.co.jp>,
	linux-kernel@...r.kernel.org
Subject: Re: mount -o loop with truncated dosdisk.img uses 100% cpu and
 can't be killed

On Thu, 2012-07-12 at 16:28 +0200, Stevie Trujillo wrote: 
> Hello,
> 
> I was trying to create a bootdisk to update my BIOS, and accidentially
> made a 512byte image with only the FreeDOS header in it.
> 
> ( Linux 3.4.4 )
> # mount -o loop dosdisk.img /tmp
> ^C^C^C
> It uses 100% CPU and doesn't listen to me when I do ^C, kill -9 etc. I
> think this means it's stuck in the kernel?

Here is the stack trace I get for the mount process:

[root@...ezart smagnani]# cat /proc/1334/stack
[<ffffffff81077a5a>] __cond_resched+0x2a/0x40
[<ffffffff8110c4bb>] find_lock_page+0x3b/0x80
[<ffffffff8110cbaf>] find_or_create_page+0x3f/0xb0
[<ffffffff8119a692>] __getblk+0xf2/0x2a0
[<ffffffff8119a893>] __bread+0x13/0xb0
[<ffffffffa00fd1fe>] fat__get_entry+0x14e/0x220 [fat]
[<ffffffffa00fd596>] fat_get_short_entry+0x66/0xc0 [fat]
[<ffffffffa00ff765>] fat_subdirs+0x55/0x80 [fat]
[<ffffffffa0103d30>] fat_fill_super+0x810/0xa80 [fat]
[<ffffffffa00e821a>] vfat_fill_super+0x1a/0x20 [vfat]
[<ffffffff8116d61b>] mount_bdev+0x1cb/0x210
[<ffffffffa00e81f5>] vfat_mount+0x15/0x20 [vfat]
[<ffffffff8116e410>] mount_fs+0x20/0xd0
[<ffffffff81186e4f>] vfs_kern_mount+0x6f/0x100
[<ffffffff81187804>] do_kern_mount+0x54/0x110
[<ffffffff811891d6>] do_mount+0x306/0x8b0
[<ffffffff811898cd>] sys_mount+0x8d/0xe0
[<ffffffff81583629>] system_call_fastpath+0x16/0x1b
[<ffffffffffffffff>] 0xffffffffffffffff

I would think this is more likely a bug in the loopback driver than the
FAT filesystem...
------------------------------------------------------------------------
Steven J. Magnani               "I claim this network for MARS!
www.digidescorp.com              Earthling, return my space modulator!"

#include <standard.disclaimer>


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