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Message-ID: <20160311124238.GN6375@twins.programming.kicks-ass.net>
Date: Fri, 11 Mar 2016 13:42:38 +0100
From: Peter Zijlstra <peterz@...radead.org>
To: Juergen Gross <jgross@...e.com>
Cc: linux-kernel@...r.kernel.org, xen-devel@...ts.xenproject.org,
konrad.wilk@...cle.com, boris.ostrovsky@...cle.com,
david.vrabel@...rix.com, mingo@...hat.com,
Douglas_Warzecha@...l.com, pali.rohar@...il.com, jdelvare@...e.com,
linux@...ck-us.net, tglx@...utronix.de, hpa@...or.com,
x86@...nel.org
Subject: Re: [PATCH 2/6] sched: add function to execute a function
synchronously on a physical cpu
On Fri, Mar 11, 2016 at 01:19:50PM +0100, Peter Zijlstra wrote:
> On Fri, Mar 11, 2016 at 12:59:30PM +0100, Juergen Gross wrote:
> > +int call_sync_on_phys_cpu(unsigned cpu, int (*func)(void *), void *par)
> > +{
> > + cpumask_var_t old_mask;
> > + int ret;
> > +
> > + if (cpu >= nr_cpu_ids)
> > + return -EINVAL;
> > +
> > + if (!alloc_cpumask_var(&old_mask, GFP_KERNEL))
> > + return -ENOMEM;
> > +
> > + cpumask_copy(old_mask, ¤t->cpus_allowed);
> > + ret = set_cpus_allowed_ptr(current, cpumask_of(cpu));
> > + if (ret)
> > + goto out;
>
> So what happens if someone does sched_setaffinity() right about here?
>
> > +
> > + ret = func(par);
> > +
> > + set_cpus_allowed_ptr(current, old_mask);
> > +
> > +out:
> > + free_cpumask_var(old_mask);
> > + return ret;
> > +}
> > +EXPORT_SYMBOL_GPL(call_sync_on_phys_cpu);
>
> This is disgusting, and you're adding this to !Xen kernels too.
how about something like:
struct xen_callback_struct {
struct work_struct work;
struct completion done;
void * data;
int ret;
};
static void xen_callback_f(struct work_struct *work)
{
struct xen_callback_struct *xcs = container_of(work, struct xen_callback_struct, work);
xcs->ret = xcs->func(xcs->data);
complete(&xcs->done);
}
xen_call_on_cpu_sync(int cpu, int (*func)(void *), void *data)
{
struct xen_callback_state xcs = {
.work = __WORK_INITIALIZER(xcs.work, xen_callback_f);
.done = COMPLETION_INITIALIZER_ONSTACK(xcs.done),
.data = data,
};
queue_work_on(&work, cpu);
wait_for_completion(&xcs.done);
return xcs.ret;
}
No mucking about with the scheduler state, no new exported functions
etc..
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