Commit 01ac33c1 authored Apr 08, 2015 by Jason Low Committed by Ingo Molnar Apr 09, 2015

locking/mutex: Further simplify mutex_spin_on_owner()



Similar to what Linus suggested for rwsem_spin_on_owner(), in
mutex_spin_on_owner() instead of having while (true) and
breaking out of the spin loop on lock->owner != owner, we can
have the loop directly check for while (lock->owner == owner) to
improve the readability of the code.

It also shrinks the code a bit:

   text    data     bss     dec     hex filename
   3721       0       0    3721     e89 mutex.o.before
   3705       0       0    3705     e79 mutex.o.after

Signed-off-by: Jason Low <jason.low2@hp.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Aswin Chandramouleeswaran <aswin@hp.com>
Cc: Davidlohr Bueso <dave@stgolabs.net>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Tim Chen <tim.c.chen@linux.intel.com>
Link: http://lkml.kernel.org/r/1428521960-5268-2-git-send-email-jason.low2@hp.com


[ Added code generation info. ]
Signed-off-by: Ingo Molnar <mingo@kernel.org>

parent 7bd3e239

kernel/locking/mutex.c

+4 −10

Original line number	Diff line number	Diff line
		@@ -224,20 +224,14 @@ ww_mutex_set_context_slowpath(struct ww_mutex *lock,
		static noinline
		bool mutex_spin_on_owner(struct mutex lock, struct task_struct owner)
		{
		bool ret;
		bool ret = true;

		rcu_read_lock();
		while (true) {
		/* Return success when the lock owner changed */
		if (lock->owner != owner) {
		ret = true;
		break;
		}

		while (lock->owner == owner) {
		/*
		* Ensure we emit the owner->on_cpu, dereference _after_
		* checking lock->owner still matches owner, if that fails,
		* owner might point to free()d memory, if it still matches,
		* checking lock->owner still matches owner. If that fails,
		* owner might point to freed memory. If it still matches,
		* the rcu_read_lock() ensures the memory stays valid.
		*/
		barrier();