Hi Song,

On 08/13/2018 10:42 PM, Song Liu wrote:

On Mon, Aug 13, 2018 at 6:17 AM, Oleg Nesterov [off-list ref] wrote:

quoted

On 08/13, Ravi Bangoria wrote:

quoted

quoted

But damn, process creation (exec) is trivial. We could add a new uprobe_exec()
hook and avoid delayed_uprobe_install() in uprobe_mmap().

I'm sorry. I didn't get this.

Sorry for confusion...

I meant, if only exec*( could race with _register(), we could add another uprobe
hook which updates all (delayed) counters before return to user-mode.

quoted

quoted

Afaics, the really problematic case is dlopen() which can race with _register()
too, right?

dlopen() should internally use mmap() right? So what is the problem here? Can
you please elaborate.

What I tried to say is that we can't avoid uprobe_mmap()->delayed_uprobe_install()
because dlopen() can race with _register() too, just like exec.

Oleg.

How about we do delayed_uprobe_install() per file? Say we keep a list
of delayed_uprobe
in load_elf_binary(). Then we can install delayed_uprobe after loading
all sections of the
file.

I'm not sure if I totally understood the idea. But how this approach can
solve dlopen() race with _register()?

Rather, making delayed_uprobe_list an mm field seems simple and effective
idea to me. The only overhead will be list_empty(mm->delayed_list) check.

Please let me know if I misunderstood you.

Thanks,
Ravi