fs/locks: Replace lg_local with a per-cpu spinlock

As Oleg suggested, replace file_lock_list with a structure containing
the hlist head and a spinlock.

This completely removes the lglock from fs/locks.

Suggested-by: Oleg Nesterov <oleg@redhat.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Al Viro <viro@ZenIV.linux.org.uk>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: dave@stgolabs.net
Cc: der.herr@hofr.at
Cc: paulmck@linux.vnet.ibm.com
Cc: riel@redhat.com
Cc: tj@kernel.org
Cc: linux-kernel@vger.kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>

fs/Kconfig

@@ -79,6 +79,7 @@ config EXPORTFS_BLOCK_OPS
 config FILE_LOCKING
 	bool "Enable POSIX file locking API" if EXPERT
 	default y
+	select PERCPU_RWSEM
 	help
 	  This option enables standard file locking support, required
           for filesystems like NFS and for the flock() system