From: Jason Low Date: Wed, 8 Apr 2015 19:39:19 +0000 (-0700) Subject: locking/mutex: Further simplify mutex_spin_on_owner() X-Git-Tag: submit/tizen/20160607.132125~2717^2~3 X-Git-Url: http://review.tizen.org/git/?a=commitdiff_plain;h=01ac33c1f907b366dcc50551316b372f1519cca9;p=sdk%2Femulator%2Femulator-kernel.git 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 Cc: Andrew Morton Cc: Aswin Chandramouleeswaran Cc: Davidlohr Bueso Cc: Linus Torvalds Cc: Paul E. McKenney Cc: Peter Zijlstra Cc: Thomas Gleixner Cc: Tim Chen 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 --- diff --git a/kernel/locking/mutex.c b/kernel/locking/mutex.c index 16b2d3c..4cccea6 100644 --- a/kernel/locking/mutex.c +++ b/kernel/locking/mutex.c @@ -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();