On Wed, 2010-06-16 at 18:41 +0200, stephane eranian wrote:
> On Wed, Jun 16, 2010 at 4:52 PM, Peter Zijlstra <pet...@infradead.org> wrote:
> > On Wed, 2010-06-16 at 16:40 +0200, Stephane Eranian wrote:
> >> This leads me to another point. For per-thread sampling, why
> >> do we need to record mmap() events happening *outside* of
> >> the process? I can understand the exception of kernel modules.
> >
> > How does that happen? The per-thread events should be on the per-task
> > context, so another task's mmap() events should never end up there.
> >
>
> I don't see the test that says the vma does not belong to the current task.
> I also don't see anything in perf_event_mmap_match().
>
> It does seem to work as you said in recent kernels, though. So I am certainly
> missing something here.
vma's are always part of the current task, its impossible to call mmap()
on another process's address space.
Look at the tail of perf_event_mmap_event(), it does:
rcu_read_lock();
cpuctx = &get_cpu_var(perf_cpu_context);
perf_event_mmap_ctx(&cpuctx->ctx, mmap_event, vma->vm_flags & VM_EXEC);
ctx = rcu_dereference(current->perf_event_ctxp);
if (ctx)
perf_event_mmap_ctx(ctx, mmap_event, vma->vm_flags & VM_EXEC);
put_cpu_var(perf_cpu_context);
rcu_read_unlock();
There it traverses the per-cpu context and the per-task context.
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