Re: possible deadlock in lru_add_drain_all

[Dmitry Vyukov]

On Wed, Feb 14, 2018 at 4:44 PM, Michal Hocko <mhocko@xxxxxxxxxx> wrote:
>> >> > > > [...]
>> >> > > > > If we want to save those stacks; we have to save a stacktrace on _every_
>> >> > > > > lock acquire, simply because we never know ahead of time if there will
>> >> > > > > be a new link. Doing this is _expensive_.
>> >> > > > >
>> >> > > > > Furthermore, the space into which we store stacktraces is limited;
>> >> > > > > since memory allocators use locks we can't very well use dynamic memory
>> >> > > > > for lockdep -- that would give recursive and robustness issues.
>> >> >
>> >> > I agree with all you said.
>> >> >
>> >> > But, I have a better idea, that is, to save only the caller's ip of each
>> >> > acquisition as an additional information? Of course, it's not enough in
>> >> > some cases, but it's cheep and better than doing nothing.
>> >> >
>> >> > For example, when building A->B, let's save not only full stack of B,
>> >> > but also caller's ip of A together, then use them on warning like:
>> >>
>> >> Like said; I've never really had trouble finding where we take A. And
>> >
>> > Me, either, since I know the way. But I've seen many guys who got
>> > confused with it, which is why I suggested it.
>> >
>> > But, leave it if you don't think so.
>> >
>> >> for the most difficult cases, just the IP isn't too useful either.
>> >>
>> >> So that would solve a non problem while leaving the real problem.
>>
>>
>> Hi,
>>
>> What's the status of this? Was any patch submitted for this?
>
> This http://lkml.kernel.org/r/20171116120535.23765-1-mhocko@xxxxxxxxxx?

Thanks

Let's tell syzbot:

#syz fix: mm: drop hotplug lock from lru_add_drain_all()