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SubjectRe: [PATCH] sched: correct testing need_resched in mutex_spin_on_owner()
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On Tue, 2011-06-07 at 21:41 +0800, Hillf Danton wrote:
> It is suppose to check the owner task that is not absolutly running on the
> local CPU,

Oh, why do you think so?

> and if NEED_RESCHED is happenly set on the current task of local
> CPU, we get incorrect result.

Only if your above assumption holds, which it doesn't. It explicitly
checks to see if _this_ cpu needs a resched while spinning, if so it
bails the spinning and calls schedule in the lock slow path.

If the owner cpu reschedules, owner will leave the rq and
owner_running() will return false, also breaking the loop.

>
> Signed-off-by: Hillf Danton <dhillf@gmail.com>
> ---
> kernel/sched.c | 2 +-
> 1 files changed, 1 insertions(+), 1 deletions(-)
>
> diff --git a/kernel/sched.c b/kernel/sched.c
> index fd18f39..3ea64fe 100644
> --- a/kernel/sched.c
> +++ b/kernel/sched.c
> @@ -4326,7 +4326,7 @@ int mutex_spin_on_owner(struct mutex *lock,
> struct task_struct *owner)
> return 0;
>
> while (owner_running(lock, owner)) {
> - if (need_resched())
> + if (test_tsk_need_resched(owner))
> return 0;
>
> arch_mutex_cpu_relax();



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