• Jan Kara's avatar
    loop: Fix mount(2) failure due to race with LOOP_SET_FD · 89e524c0
    Jan Kara authored
    Commit 33ec3e53 ("loop: Don't change loop device under exclusive
    opener") made LOOP_SET_FD ioctl acquire exclusive block device reference
    while it updates loop device binding. However this can make perfectly
    valid mount(2) fail with EBUSY due to racing LOOP_SET_FD holding
    temporarily the exclusive bdev reference in cases like this:
    
    for i in {a..z}{a..z}; do
            dd if=/dev/zero of=$i.image bs=1k count=0 seek=1024
            mkfs.ext2 $i.image
            mkdir mnt$i
    done
    
    echo "Run"
    for i in {a..z}{a..z}; do
            mount -o loop -t ext2 $i.image mnt$i &
    done
    
    Fix the problem by not getting full exclusive bdev reference in
    LOOP_SET_FD but instead just mark the bdev as being claimed while we
    update the binding information. This just blocks new exclusive openers
    instead of failing them with EBUSY thus fixing the problem.
    
    Fixes: 33ec3e53 ("loop: Don't change loop device under exclusive opener")
    Cc: stable@vger.kernel.org
    Tested-by: default avatarKai-Heng Feng <kai.heng.feng@canonical.com>
    Signed-off-by: default avatarJan Kara <jack@suse.cz>
    Signed-off-by: default avatarJens Axboe <axboe@kernel.dk>
    89e524c0
fs.h 115 KB