* Jason Low <jason.l...@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.l...@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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