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

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Date:	Fri, 13 Jul 2012 04:49:47 +0900
From:	OGAWA Hirofumi <hirofumi@...l.parknet.co.jp>
To:	"Steven J. Magnani" <steve@...idescorp.com>
Cc:	Stevie Trujillo <stevie.trujillo@...il.com>,
	linux-kernel@...r.kernel.org, Jens Axboe <axboe@...nel.dk>
Subject: Re: mount -o loop with truncated dosdisk.img uses 100% cpu and can't be killed

"Steven J. Magnani" <steve@...idescorp.com> writes:

>> 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 <hirofumi@...l.parknet.co.jp>
>> ---
>> 
>>  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;
>> _
>
> This fixes the hang, but I'm not sure dump_stack() is a good idea. I get
> almost 100 lines of stack dumps and error messages in my kernel log.
> Also, I was a little surprised to see that mount completes successfully.

So, it sounds like the good choice would be (b) or (c). Well, I guess
Jens would choose what to do.
-- 
OGAWA Hirofumi <hirofumi@...l.parknet.co.jp>
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