Messages in this thread | | | Date | Tue, 10 Mar 2015 09:11:48 +0100 | From | Ingo Molnar <> | Subject | Re: [PATCH] locking/mutex: Refactor mutex_spin_on_owner() |
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* Jason Low <jason.low2@hp.com> wrote:
> This patch applies on top of tip. > > ------------------------------------------------------------------- > 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). This improves the > readability of the code. > > Signed-off-by: Jason Low <jason.low2@hp.com> > --- > kernel/locking/mutex.c | 17 +++++------------ > 1 files changed, 5 insertions(+), 12 deletions(-) > > diff --git a/kernel/locking/mutex.c b/kernel/locking/mutex.c > index 16b2d3c..1c3b7c5 100644 > --- a/kernel/locking/mutex.c > +++ b/kernel/locking/mutex.c > @@ -224,16 +224,8 @@ 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; > - > 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, > @@ -242,16 +234,17 @@ bool mutex_spin_on_owner(struct mutex *lock, struct task_struct *owner) > */ > barrier(); > > + /* Stop spinning when need_resched or owner is not running. */ > if (!owner->on_cpu || need_resched()) { > - ret = false; > - break; > + rcu_read_unlock(); > + return false; > } > > cpu_relax_lowlatency(); > } > rcu_read_unlock(); > > - return ret; > + return true;
A nit: having multiple return statements in a function is not the cleanest approach, especially when we are holding locks.
It's better to add an 'out_unlock' label to before the rcu_read_unlock() and use that plus 'ret'.
Thanks,
Ingo
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