• Yan, Zheng's avatar
    ceph: fix race in concurrent readdir · 84583cfb
    Yan, Zheng authored
    For a large directory, program needs to issue multiple readdir
    syscalls to get all dentries. When there are multiple programs
    read the directory concurrently. Following sequence of events
    can happen.
    
     - program calls readdir with pos = 2. ceph sends readdir request
       to mds. The reply contains N1 entries. ceph adds these N1 entries
       to readdir cache.
     - program calls readdir with pos = N1+2. The readdir is satisfied
       by the readdir cache, N2 entries are returned. (Other program
       calls readdir in the middle, which fills the cache)
     - program calls readdir with pos = N1+N2+2. ceph sends readdir
       request to mds. The reply contains N3 entries and it reaches
       directory end. ceph adds these N3 entries to the readdir cache
       and marks directory complete.
    
    The second readdir call does not update fi->readdir_cache_idx.
    ceph add the last N3 entries to wrong places.
    
    Cc: stable@vger.kernel.org # v4.3+
    Signed-off-by: default avatar"Yan, Zheng" <zyan@redhat.com>
    Signed-off-by: default avatarIlya Dryomov <idryomov@gmail.com>
    84583cfb
dir.c 39.9 KB