• Sachin Prabhu's avatar
    cifs: Wait for writebacks to complete before attempting write. · c11f1df5
    Sachin Prabhu authored
    Problem reported in Red Hat bz 1040329 for strict writes where we cache
    only when we hold oplock and write direct to the server when we don't.
    
    When we receive an oplock break, we first change the oplock value for
    the inode in cifsInodeInfo->oplock to indicate that we no longer hold
    the oplock before we enqueue a task to flush changes to the backing
    device. Once we have completed flushing the changes, we return the
    oplock to the server.
    
    There are 2 ways here where we can have data corruption
    1) While we flush changes to the backing device as part of the oplock
    break, we can have processes write to the file. These writes check for
    the oplock, find none and attempt to write directly to the server.
    These direct writes made while we are flushing from cache could be
    overwritten by data being flushed from the cache causing data
    corruption.
    2) While a thread runs in cifs_strict_writev, the machine could receive
    and process an oplock break after the thread has checked the oplock and
    found that it allows us to cache and before we have made changes to the
    cache. In that case, we end up with a dirty page in cache when we
    shouldn't have any. This will be flushed later and will overwrite all
    subsequent writes to the part of the file represented by this page.
    
    Before making any writes to the server, we need to confirm that we are
    not in the process of flushing data to the server and if we are, we
    should wait until the process is complete before we attempt the write.
    We should also wait for existing writes to complete before we process
    an oplock break request which changes oplock values.
    
    We add a version specific  downgrade_oplock() operation to allow for
    differences in the oplock values set for the different smb versions.
    
    Cc: stable@vger.kernel.org
    Signed-off-by: default avatarSachin Prabhu <sprabhu@redhat.com>
    Reviewed-by: default avatarJeff Layton <jlayton@redhat.com>
    Reviewed-by: default avatarPavel Shilovsky <piastry@etersoft.ru>
    Signed-off-by: default avatarSteve French <smfrench@gmail.com>
    c11f1df5
misc.c 18.2 KB