From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756317Ab2GMPoA (ORCPT ); Fri, 13 Jul 2012 11:44:00 -0400 Received: from cantor2.suse.de ([195.135.220.15]:56226 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752691Ab2GMPn6 (ORCPT ); Fri, 13 Jul 2012 11:43:58 -0400 Date: Fri, 13 Jul 2012 17:43:54 +0200 From: Jan Kara To: OGAWA Hirofumi Cc: "Steven J. Magnani" , Stevie Trujillo , linux-kernel@vger.kernel.org, Jens Axboe , Jeff Moyer Subject: Re: mount -o loop with truncated dosdisk.img uses 100% cpu and can't be killed Message-ID: <20120713154354.GD28715@quack.suse.cz> References: <20120712162828.3f561315@localhost> <1342106206.2156.2.camel@iscandar.digidescorp.com> <87k3y8yed3.fsf@devron.myhome.or.jp> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <87k3y8yed3.fsf@devron.myhome.or.jp> User-Agent: Mutt/1.5.20 (2009-06-14) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri 13-07-12 04:21:44, OGAWA Hirofumi wrote: > "Steven J. Magnani" writes: > > > 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@telezart smagnani]# cat /proc/1334/stack > > [] __cond_resched+0x2a/0x40 > > [] find_lock_page+0x3b/0x80 > > [] find_or_create_page+0x3f/0xb0 > > [] __getblk+0xf2/0x2a0 > > [] __bread+0x13/0xb0 > > [] fat__get_entry+0x14e/0x220 [fat] > > [] fat_get_short_entry+0x66/0xc0 [fat] > > [] fat_subdirs+0x55/0x80 [fat] > > [] fat_fill_super+0x810/0xa80 [fat] > > [] vfat_fill_super+0x1a/0x20 [vfat] > > [] mount_bdev+0x1cb/0x210 > > [] vfat_mount+0x15/0x20 [vfat] > > [] mount_fs+0x20/0xd0 > > [] vfs_kern_mount+0x6f/0x100 > > [] do_kern_mount+0x54/0x110 > > [] do_mount+0x306/0x8b0 > > [] sys_mount+0x8d/0xe0 > > [] system_call_fastpath+0x16/0x1b > > [] 0xffffffffffffffff > > > > I would think this is more likely a bug in the loopback driver than the > > FAT filesystem... > > It looks like the bug of __getblk_slow(). If requested block was beyond > end of device, __find_get_block() will find buffer_mapped()'s buffer, > but block >= end_block is unmapped. So, it can be loop. > > The following patch fixes it? If it fix, there are some options to check > it. > > a) Check it like this patch and warn. > b) (a), but without warn. > c) Check it in init_page_buffers() and return -EIO or such > > Well, anyway, Cc to Jens. > > Signed-off-by: OGAWA Hirofumi I think Jeff Moyer has sent a similar fix recently. It may even be already queued in Jens' tree. Jeff? Honza > --- > > fs/buffer.c | 7 +++++++ > 1 file changed, 7 insertions(+) > > diff -puN fs/buffer.c~debug fs/buffer.c > --- tux3fs/fs/buffer.c~debug 2012-07-13 04:10:40.000000000 +0900 > +++ tux3fs-hirofumi/fs/buffer.c 2012-07-13 04:11:50.000000000 +0900 > @@ -1055,6 +1055,13 @@ __getblk_slow(struct block_device *bdev, > dump_stack(); > return NULL; > } > + if (block >= blkdev_max_block(I_BDEV(bdev->bd_inode))) { > + printk(KERN_ERR "getblk(): block %llu, end_block %llu\n", > + (unsigned long long)block, > + (unsigned long long)blkdev_max_block(I_BDEV(bdev->bd_inode))); > + dump_stack(); > + return NULL; > + } > > for (;;) { > struct buffer_head * bh; > _ > > -- > OGAWA Hirofumi > -- > To unsubscribe from this list: send the line "unsubscribe linux-kernel" in > the body of a message to majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html > Please read the FAQ at http://www.tux.org/lkml/ -- Jan Kara SUSE Labs, CR