Re: [PATCH -mm 3/3] proc: make task_sig() lockless

[David Howells <dhowells@redhat.com>]

Oleg Nesterov <oleg@redhat.com> wrote:

> > Except that the data returned might then be inconsistent because you don't
> > hold a lock as you read the various bits of it.
> 
> Yes. From the changelog:
> 
> 	Of course, this means we read pending/blocked/etc nonatomically,
> 	but I hope this is OK for fs/proc.

Ah, yes.  I read that as you meant how procfs accessed the actual data
structures, not how the user accessed procfs.  It might be worth clarifying
that.

> But I don't think the returned data could be "really" inconsistent
> from the /bin/ps pov. Yes, it is possible that, say, some signal is
> seen as both pending and ignored without ->siglock. Or we can report
> user->sigpending != 0 while pending/shpending are empty.
> 
> But this looks harmless to me. We never guaranteed /proc/pid/status
> can't report the "intermediate" state, and I don't think we can
> confuse the user-space.
> 
> Do you agree? Or do you think this can make problems ?

I don't know of anything this will affect adversely.  In fact, I'm not sure
there was a guarantee that it would be atomic anyway.

So as far as I'm concerned, you can add:

Acked-by: David Howells <dhowells@redhat.com>

> > Probably we can change do_task_stat() to avod ->siglock too, except
> > we can't get tty_nr lockless.

Btw, avoid has an 'i' in it... :-)