You should be CCing WQ maintainers on changes like this one (now added).
On Tue 30-05-23 11:52:37, Marcelo Tosatti wrote:
> Add a schedule_on_each_cpumask function, equivalent to
> schedule_on_each_cpu but accepting a cpumask to operate.
IMHO it is preferable to add a new function along with its user so that
the usecase is more clear.
> Signed-off-by: Marcelo Tosatti <mtosatti@xxxxxxxxxx>
>
> ---
>
> Index: linux-vmstat-remote/kernel/workqueue.c
> ===================================================================
> --- linux-vmstat-remote.orig/kernel/workqueue.c
> +++ linux-vmstat-remote/kernel/workqueue.c
> @@ -3455,6 +3455,56 @@ int schedule_on_each_cpu(work_func_t fun
> return 0;
> }
>
> +
> +/**
> + * schedule_on_each_cpumask - execute a function synchronously on each
> + * CPU in "cpumask", for those which are online.
> + *
> + * @func: the function to call
> + * @mask: the CPUs which to call function on
> + *
> + * schedule_on_each_cpu() executes @func on each specified CPU that is online,
> + * using the system workqueue and blocks until all such CPUs have completed.
> + * schedule_on_each_cpu() is very slow.
> + *
> + * Return:
> + * 0 on success, -errno on failure.
> + */
> +int schedule_on_each_cpumask(work_func_t func, cpumask_t *cpumask)
> +{
> + int cpu;
> + struct work_struct __percpu *works;
> + cpumask_var_t effmask;
> +
> + works = alloc_percpu(struct work_struct);
> + if (!works)
> + return -ENOMEM;
> +
> + if (!alloc_cpumask_var(&effmask, GFP_KERNEL)) {
> + free_percpu(works);
> + return -ENOMEM;
> + }
> +
> + cpumask_and(effmask, cpumask, cpu_online_mask);
> +
> + cpus_read_lock();
> +
> + for_each_cpu(cpu, effmask) {
Is the cpu_online_mask dance really necessary? Why cannot you simply do
for_each_online_cpu here? flush_work on unqueued work item should just
return, no?
Also there is no synchronization with the cpu hotplug so cpu_online_mask
can change under your feet so this construct seem unsafe to me.
> + struct work_struct *work = per_cpu_ptr(works, cpu);
> +
> + INIT_WORK(work, func);
> + schedule_work_on(cpu, work);
> + }
> +
> + for_each_cpu(cpu, effmask)
> + flush_work(per_cpu_ptr(works, cpu));
> +
> + cpus_read_unlock();
> + free_percpu(works);
> + free_cpumask_var(effmask);
> + return 0;
> +}
> +
> /**
> * execute_in_process_context - reliably execute the routine with user context
> * @fn: the function to execute
> Index: linux-vmstat-remote/include/linux/workqueue.h
> ===================================================================
> --- linux-vmstat-remote.orig/include/linux/workqueue.h
> +++ linux-vmstat-remote/include/linux/workqueue.h
> @@ -450,6 +450,7 @@ extern void __flush_workqueue(struct wor
> extern void drain_workqueue(struct workqueue_struct *wq);
>
> extern int schedule_on_each_cpu(work_func_t func);
> +extern int schedule_on_each_cpumask(work_func_t func, cpumask_t *cpumask);
>
> int execute_in_process_context(work_func_t fn, struct execute_work *);
>
>
--
Michal Hocko
SUSE Labs
