• Vladimir Davydov's avatar
    cleancache: forbid overriding cleancache_ops · 53d85c98
    Vladimir Davydov authored
    
    
    Currently, cleancache_register_ops returns the previous value of
    cleancache_ops to allow chaining.  However, chaining, as it is
    implemented now, is extremely dangerous due to possible pool id
    collisions.  Suppose, a new cleancache driver is registered after the
    previous one assigned an id to a super block.  If the new driver assigns
    the same id to another super block, which is perfectly possible, we will
    have two different filesystems using the same id.  No matter if the new
    driver implements chaining or not, we are likely to get data corruption
    with such a configuration eventually.
    
    This patch therefore disables the ability to override cleancache_ops
    altogether as potentially dangerous.  If there is already cleancache
    driver registered, all further calls to cleancache_register_ops will
    return EBUSY.  Since no user of cleancache implements chaining, we only
    need to make minor changes to the code outside the cleancache core.
    Signed-off-by: default avatarVladimir Davydov <vdavydov@parallels.com>
    Cc: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
    Cc: Boris Ostrovsky <boris.ostrovsky@oracle.com>
    Cc: David Vrabel <david.vrabel@citrix.com>
    Cc: Mark Fasheh <mfasheh@suse.com>
    Cc: Joel Becker <jlbec@evilplan.org>
    Cc: Stefan Hengelein <ilendir@googlemail.com>
    Cc: Florian Schmaus <fschmaus@gmail.com>
    Cc: Andor Daam <andor.daam@googlemail.com>
    Cc: Dan Magenheimer <dan.magenheimer@oracle.com>
    Cc: Bob Liu <lliubbo@gmail.com>
    Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
    Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
    53d85c98