• Jeff Moyer's avatar
    block: don't mark buffers beyond end of disk as mapped · 080399aa
    Jeff Moyer authored
    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: default avatarJeff Moyer <jmoyer@redhat.com>
    Acked-by: default avatarNick Piggin <npiggin@kernel.dk>
    
    --
    
    Changes from v1->v2: re-used max_block, as suggested by Nick Piggin.
    Signed-off-by: default avatarJens Axboe <axboe@kernel.dk>
    080399aa
buffer.c 85.5 KB