From 080399aaaf3531f5b8761ec0ac30ff98891e8686 Mon Sep 17 00:00:00 2001 From: Jeff Moyer Date: Fri, 11 May 2012 16:34:10 +0200 Subject: [PATCH] block: don't mark buffers beyond end of disk as mapped 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 Acked-by: Nick Piggin -- Changes from v1->v2: re-used max_block, as suggested by Nick Piggin. Signed-off-by: Jens Axboe --- fs/block_dev.c | 6 +++--- fs/buffer.c | 4 +++- include/linux/fs.h | 1 + 3 files changed, 7 insertions(+), 4 deletions(-) diff --git a/fs/block_dev.c b/fs/block_dev.c index e08f6a20a5bb..ba11c30f302d 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 351e18ea2e53..ad5938ca357c 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 8de675523e46..25c40b9f848a 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 *); -- 2.30.2