On Tue, Aug 23, 2016 at 01:52:46PM -0700, Tim Chen wrote:
> On Tue, 2016-08-23 at 15:55 -0400, Waiman Long wrote:
> > On 08/23/2016 08:46 AM, Peter Zijlstra wrote:
> >
> > I have 2 more comments about the code.
> > 1) There are a couple of places where you only use 0x3 in mutex.c. They
> > should be replaced by the symbolic name instead.
>
> May be easier to read if (owner & 0x3) and
> (owner & ~0x3) are changed to something like
> _owner_flag(owner) and _owner_task(owner).
Yes that would work. Something like the below..
Note the ';' in the last "-" line that currently ensures we always take
the slow path.
----
--- a/kernel/locking/mutex.c
+++ b/kernel/locking/mutex.c
@@ -55,7 +55,17 @@ EXPORT_SYMBOL(__mutex_init);
#define MUTEX_FLAG_WAITERS 0x01
#define MUTEX_FLAG_HANDOFF 0x02
-#define MUTEX_FLAG_ALL 0x03
+#define MUTEX_FLAGS 0x03
+
+static inline struct task_struct *__owner_task(unsigned long owner)
+{
+ return (struct task_struct *)(owner & ~MUTEX_FLAGS);
+}
+
+static inline unsigned long __owner_flags(unsigned long owner)
+{
+ return owner & MUTEX_FLAGS;
+}
/*
* Atomically try to take the lock when it is available
@@ -65,7 +75,7 @@ static inline bool __mutex_trylock(struc
unsigned long owner, new_owner;
owner = atomic_long_read(&lock->owner);
- if (owner & ~0x03)
+ if (__owner_task(owner))
return false;
new_owner = owner | (unsigned long)current;
@@ -466,14 +476,14 @@ void __sched mutex_unlock(struct mutex *
if (owner & MUTEX_FLAG_HANDOFF)
break;
- old = atomic_long_cmpxchg_release(&lock->owner, owner, owner &
0x03);
+ old = atomic_long_cmpxchg_release(&lock->owner, owner,
__owner_flags(owner));
if (old == owner)
break;
owner = old;
}
- if (owner & 0x03);
+ if (__owner_flags(owner))
__mutex_unlock_slowpath(lock, owner);
}
EXPORT_SYMBOL(mutex_unlock);
