• Miklos Szeredi's avatar
    [PATCH] remove steal_locks() · c89681ed
    Miklos Szeredi authored
    This patch removes the steal_locks() function.
    
    steal_locks() doesn't work correctly with any filesystem that does it's own
    lock management, including NFS, CIFS, etc.
    
    In addition it has weird semantics on local filesystems in case tasks
    sharing file-descriptor tables are doing POSIX locking operations in
    parallel to execve().
    
    The steal_locks() function has an effect on applications doing:
    
    clone(CLONE_FILES)
      /* in child */
      lock
      execve
      lock
    
    POSIX locks acquired before execve (by "child", "parent" or any further
    task sharing files_struct) will after the execve be owned exclusively by
    "child".
    
    According to Chris Wright some LSB/LTP kind of suite triggers without the
    stealing behavior, but there's no known real-world application that would
    also fail.
    
    Apps using NPTL are not affected, since all other threads are killed before
    execve.
    
    Apps using LinuxThreads are only affected if they
    
      - have multiple threads during exec (LinuxThreads doesn't kill other
        threads, the app may do it with pthread_kill_other_threads_np())
      - rely on POSIX locks being inherited across exec
    
    Both conditions are documented, but not their interaction.
    
    Apps using clone() natively are affected if they
    
      - use clone(CLONE_FILES)
      - rely on POSIX locks being inherited across exec
    
    The above scenarios are unlikely, but possible.
    
    If the patch is vetoed, there's a plan B, that involves mostly keeping the
    weird stealing semantics, but changing the way lock ownership is handled so
    that network and local filesystems work consistently.
    
    That would add more complexity though, so this solution seems to be
    preferred by most people.
    Signed-off-by: default avatarMiklos Szeredi <miklos@szeredi.hu>
    Cc: Trond Myklebust <trond.myklebust@fys.uio.no>
    Cc: Matthew Wilcox <willy@debian.org>
    Cc: Chris Wright <chrisw@sous-sol.org>
    Cc: Christoph Hellwig <hch@lst.de>
    Cc: Steven French <sfrench@us.ibm.com>
    Signed-off-by: default avatarAndrew Morton <akpm@osdl.org>
    Signed-off-by: default avatarLinus Torvalds <torvalds@osdl.org>
    c89681ed
exec.c 35.1 KB