unix_gc() assumes that candidate sockets can never gain an external
reference (i.e. be installed into an fd) while the unix_gc_lock is
held. Except for MSG_PEEK this is guaranteed by modifying inflight
count under the unix_gc_lock.
MSG_PEEK does not touch any variable protected by unix_gc_lock (file
count is not), yet it needs to be serialized with garbage collection.
Do this by locking/unlocking unix_gc_lock:
1) increment file count
2) lock/unlock barrier to make sure incremented file count is visible
to garbage collection
3) install file into fd
This is a lock barrier (unlike smp_mb()) that ensures that garbage
collection is run completely before or completely after the barrier.
Cc: <stable@vger.kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
cbcf01128d