• Dave Wysochanski's avatar
    cifs: Fix cifsInodeInfo lock_sem deadlock when reconnect occurs · d46b0da7
    Dave Wysochanski authored
    There's a deadlock that is possible and can easily be seen with
    a test where multiple readers open/read/close of the same file
    and a disruption occurs causing reconnect.  The deadlock is due
    a reader thread inside cifs_strict_readv calling down_read and
    obtaining lock_sem, and then after reconnect inside
    cifs_reopen_file calling down_read a second time.  If in
    between the two down_read calls, a down_write comes from
    another process, deadlock occurs.
    
            CPU0                    CPU1
            ----                    ----
    cifs_strict_readv()
     down_read(&cifsi->lock_sem);
                                   _cifsFileInfo_put
                                      OR
                                   cifs_new_fileinfo
                                    down_write(&cifsi->lock_sem);
    cifs_reopen_file()
     down_read(&cifsi->lock_sem);
    
    Fix the above by changing all down_write(lock_sem) calls to
    down_write_trylock(lock_sem)/msleep() loop, which in turn
    makes the second down_read call benign since it will never
    block behind the writer while holding lock_sem.
    Signed-off-by: default avatarDave Wysochanski <dwysocha@redhat.com>
    Suggested-by: default avatarRonnie Sahlberg <lsahlber@redhat.com>
    Reviewed--by: default avatarRonnie Sahlberg <lsahlber@redhat.com>
    Reviewed-by: default avatarPavel Shilovsky <pshilov@microsoft.com>
    d46b0da7
smb2file.c 7.88 KB