Re: [RFC-PATCH 1/2] mm: Add __GFP_NO_LOCKS flag

From: Matthew Wilcox
Date: Thu Aug 13 2020 - 10:32:34 EST

On Thu, Aug 13, 2020 at 03:27:15PM +0200, Thomas Gleixner wrote:
> And guarding it with RT is not working either because then you are back
> to square one with the problem which triggered the discussion in the
> first place:
> raw_spin_lock()
> alloc()
> if (RT && !preemptible()) <- False because RT == false
> goto bail;
> spin_lock(&zone->lock) --> LOCKDEP complains
> So either you convince Paul not to do that or you need to do something
> like I suggested in my other reply.

I'd like to throw in the possibility that we do something like:

if (!spin_trylock(&zone->lock))
if (RT && !preemptible())
goto bail;

would that make us feel more comfortable about converting zone->lock to
a raw spinlock?