Re: [PATCH 6/8] trace_uprobe/sdt: Fix multiple update of same reference counter

[Oleg Nesterov]

Hi Ravi,

On 03/19, Ravi Bangoria wrote:
>
> On 03/16/2018 11:20 PM, Oleg Nesterov wrote:
> >
> > And it seems that you are trying to confuse yourself, not only me ;) Just
> > suppose that an application does mmap+munmap in a loop and the mapped region
> > contains uprobe but not the counter.
>
> this is fine because ...

Yes, I guess I tried to say "counter but not uprobe" but possibly I was actually
confused.

> Our initial design was to increment counter in install_breakpoint() but
> uprobed instruction gets patched in a very early stage of binary loading
> and vma that holds the counter may not be mapped yet.

Yes, yes, I understand this is not that simple...

> > Btw, why do we need a counter, not a boolean? Who else can modify it?
> > Or different uprobes can share the same counter?
>
> Yes, multiple SDT markers can share the counter.

OK, thanks.

Oleg.