On Fri, 23 Aug 2013 07:57:15 +0800
"zhangwei(Jovi)" <jovi.zhang...@huawei.com> wrote:
> >
> > What about creating a per cpu buffer when uprobes are registered, and
> > delete them when they are finished? Basically what trace_printk() does
> > if it detects that there are users of trace_printk() in the kernel.
> > Note, it does not deallocate them when finished, as it is never
> > finished until reboot ;-)
> >
> > -- Steve
> >
> I also thought out this approach, but the issue is we cannot fetch user
> memory into per-cpu buffer, because use per-cpu buffer should under
> preempt disabled, and fetching user memory could sleep.
Actually, we could create a per_cpu mutex to match the per_cpu buffers.
This is not unlike what we do in -rt.
int cpu;
struct mutex *mutex;
void *buf;
/*
* Use per cpu buffers for fastest access, but we might migrate
* So the mutex makes sure we have sole access to it.
*/
cpu = raw_smp_processor_id();
mutex = per_cpu(uprobe_cpu_mutex, cpu);
buf = per_cpu(uprobe_cpu_buffer, cpu);
mutex_lock(mutex);
store_trace_args(..., buf,...);
mutex_unlock(mutex);
-- Steve
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