[PATCH] remove steal_locks()

[PATCH] remove steal_locks()

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: Miklos 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: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>