Re: [patch, v2] block: don't mark buffers beyond end of disk as mapped

[Jeff Moyer <jmoyer@redhat.com>]

Jens, could you please queue this patch up?

Thanks!
Jeff


Jeff Moyer <jmoyer@redhat.com> writes:

> Hi,
>
> We have a bug report open where a squashfs image mounted on ppc64 would
> exhibit errors due to trying to read beyond the end of the disk.  It can
> easily be reproduced by doing the following:
>
> [root@ibm-p750e-02-lp3 ~]# ls -l install.img
> -rw-r--r-- 1 root root 142032896 Apr 30 16:46 install.img
> [root@ibm-p750e-02-lp3 ~]# mount -o loop ./install.img /mnt/test
> [root@ibm-p750e-02-lp3 ~]# dd if=/dev/loop0 of=/dev/null 
> dd: reading `/dev/loop0': Input/output error
> 277376+0 records in
> 277376+0 records out
> 142016512 bytes (142 MB) copied, 0.9465 s, 150 MB/s
>
> In dmesg, you'll find the following:
>
> squashfs: version 4.0 (2009/01/31) Phillip Lougher
> [   43.106012] attempt to access beyond end of device
> [   43.106029] loop0: rw=0, want=277410, limit=277408
> [   43.106039] Buffer I/O error on device loop0, logical block 138704
> [   43.106053] attempt to access beyond end of device
> [   43.106057] loop0: rw=0, want=277412, limit=277408
> [   43.106061] Buffer I/O error on device loop0, logical block 138705
> [   43.106066] attempt to access beyond end of device
> [   43.106070] loop0: rw=0, want=277414, limit=277408
> [   43.106073] Buffer I/O error on device loop0, logical block 138706
> [   43.106078] attempt to access beyond end of device
> [   43.106081] loop0: rw=0, want=277416, limit=277408
> [   43.106085] Buffer I/O error on device loop0, logical block 138707
> [   43.106089] attempt to access beyond end of device
> [   43.106093] loop0: rw=0, want=277418, limit=277408
> [   43.106096] Buffer I/O error on device loop0, logical block 138708
> [   43.106101] attempt to access beyond end of device
> [   43.106104] loop0: rw=0, want=277420, limit=277408
> [   43.106108] Buffer I/O error on device loop0, logical block 138709
> [   43.106112] attempt to access beyond end of device
> [   43.106116] loop0: rw=0, want=277422, limit=277408
> [   43.106120] Buffer I/O error on device loop0, logical block 138710
> [   43.106124] attempt to access beyond end of device
> [   43.106128] loop0: rw=0, want=277424, limit=277408
> [   43.106131] Buffer I/O error on device loop0, logical block 138711
> [   43.106135] attempt to access beyond end of device
> [   43.106139] loop0: rw=0, want=277426, limit=277408
> [   43.106143] Buffer I/O error on device loop0, logical block 138712
> [   43.106147] attempt to access beyond end of device
> [   43.106151] loop0: rw=0, want=277428, limit=277408
> [   43.106154] Buffer I/O error on device loop0, logical block 138713
> [   43.106158] attempt to access beyond end of device
> [   43.106162] loop0: rw=0, want=277430, limit=277408
> [   43.106166] attempt to access beyond end of device
> [   43.106169] loop0: rw=0, want=277432, limit=277408
> ...
> [   43.106307] attempt to access beyond end of device
> [   43.106311] loop0: rw=0, want=277470, limit=2774
>
> Squashfs manages to read in the end block(s) of the disk during the
> mount operation.  Then, when dd reads the block device, it leads to
> block_read_full_page being called with buffers that are beyond end of
> disk, but are marked as mapped.  Thus, it would end up submitting read
> I/O against them, resulting in the errors mentioned above.  I fixed the
> problem by modifying init_page_buffers to only set the buffer mapped if
> it fell inside of i_size.
>
> Cheers,
> Jeff
>
> Signed-off-by: Jeff Moyer <jmoyer@redhat.com>
> Acked-by: Nick Piggin <npiggin@kernel.dk>
>
> --
>
> Changes from v1->v2: re-used max_block, as suggested by Nick Piggin.
>
> diff --git a/fs/block_dev.c b/fs/block_dev.c
> index e08f6a2..ba11c30 100644
> --- a/fs/block_dev.c
> +++ b/fs/block_dev.c
> @@ -70,7 +70,7 @@ static void bdev_inode_switch_bdi(struct inode *inode,
>  	spin_unlock(&dst->wb.list_lock);
>  }
>  
> -static sector_t max_block(struct block_device *bdev)
> +sector_t blkdev_max_block(struct block_device *bdev)
>  {
>  	sector_t retval = ~((sector_t)0);
>  	loff_t sz = i_size_read(bdev->bd_inode);
> @@ -163,7 +163,7 @@ static int
>  blkdev_get_block(struct inode *inode, sector_t iblock,
>  		struct buffer_head *bh, int create)
>  {
> -	if (iblock >= max_block(I_BDEV(inode))) {
> +	if (iblock >= blkdev_max_block(I_BDEV(inode))) {
>  		if (create)
>  			return -EIO;
>  
> @@ -185,7 +185,7 @@ static int
>  blkdev_get_blocks(struct inode *inode, sector_t iblock,
>  		struct buffer_head *bh, int create)
>  {
> -	sector_t end_block = max_block(I_BDEV(inode));
> +	sector_t end_block = blkdev_max_block(I_BDEV(inode));
>  	unsigned long max_blocks = bh->b_size >> inode->i_blkbits;
>  
>  	if ((iblock + max_blocks) > end_block) {
> diff --git a/fs/buffer.c b/fs/buffer.c
> index 351e18e..ad5938c 100644
> --- a/fs/buffer.c
> +++ b/fs/buffer.c
> @@ -921,6 +921,7 @@ init_page_buffers(struct page *page, struct block_device *bdev,
>  	struct buffer_head *head = page_buffers(page);
>  	struct buffer_head *bh = head;
>  	int uptodate = PageUptodate(page);
> +	sector_t end_block = blkdev_max_block(I_BDEV(bdev->bd_inode));
>  
>  	do {
>  		if (!buffer_mapped(bh)) {
> @@ -929,7 +930,8 @@ init_page_buffers(struct page *page, struct block_device *bdev,
>  			bh->b_blocknr = block;
>  			if (uptodate)
>  				set_buffer_uptodate(bh);
> -			set_buffer_mapped(bh);
> +			if (block < end_block)
> +				set_buffer_mapped(bh);
>  		}
>  		block++;
>  		bh = bh->b_this_page;
> diff --git a/include/linux/fs.h b/include/linux/fs.h
> index 8de6755..25c40b9 100644
> --- a/include/linux/fs.h
> +++ b/include/linux/fs.h
> @@ -2051,6 +2051,7 @@ extern void unregister_blkdev(unsigned int, const char *);
>  extern struct block_device *bdget(dev_t);
>  extern struct block_device *bdgrab(struct block_device *bdev);
>  extern void bd_set_size(struct block_device *, loff_t size);
> +extern sector_t blkdev_max_block(struct block_device *bdev);
>  extern void bd_forget(struct inode *inode);
>  extern void bdput(struct block_device *);
>  extern void invalidate_bdev(struct block_device *);
> --
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