Re: [PATCH v2 7/9] trace_uprobe/sdt: Fix multiple update of same reference counter

[Ravi Bangoria]

Hi Oleg,

On 04/10/2018 04:36 PM, Oleg Nesterov wrote:
> Hi Ravi,
>
> On 04/10, Ravi Bangoria wrote:
>>> and what if __mmu_notifier_register() fails simply because signal_pending() == T?
>>> see mm_take_all_locks().
>>>
>>> at first glance this all look suspicious and sub-optimal,
>> Yes. I should have added checks for failure cases.
>> Will fix them in v3.
> And what can you do if it fails? Nothing except report the problem. But
> signal_pending() is not the unlikely or error condition, it should not
> cause the tracing errors.

...

> Plus mm_take_all_locks() is very heavy... BTW, uprobe_mmap_callback() is
> called unconditionally. Whatever it does, can we at least move it after
> the no_uprobe_events() check? Can't we also check MMF_HAS_UPROBES?

Sure, I'll move it after these conditions.

> Either way, I do not feel that mmu_notifier is the right tool... Did you
> consider the uprobe_clear_state() hook we already have?

Ah! This is really a good idea. We don't need mmu_notifier then.

Thanks for suggestion,
Ravi