On Thu, Aug 13, 2020 at 04:34:57PM +0200, Thomas Gleixner wrote: > Michal Hocko <mhocko@xxxxxxxx> writes: > > On Thu 13-08-20 15:22:00, Thomas Gleixner wrote: > >> It basically requires to convert the wait queue to something else. Is > >> the waitqueue strict single waiter? > > > > I would have to double check. From what I remember only kswapd should > > ever sleep on it. > > That would make it trivial as we could simply switch it over to rcu_wait. > > >> So that should be: > >> > >> if (!preemptible() && gfp == GFP_RT_NOWAIT) > >> > >> which is limiting the damage to those callers which hand in > >> GFP_RT_NOWAIT. > >> > >> lockdep will yell at invocations with gfp != GFP_RT_NOWAIT when it hits > >> zone->lock in the wrong context. And we want to know about that so we > >> can look at the caller and figure out how to solve it. > > > > Yes, that would have to somehow need to annotate the zone_lock to be ok > > in those paths so that lockdep doesn't complain. > > That opens the worst of all cans of worms. If we start this here then > Joe programmer and his dog will use these lockdep annotation to evade > warnings and when exposed to RT it will fall apart in pieces. Just that > at that point Joe programmer moved on to something else and the usual > suspects can mop up the pieces. We've seen that all over the place and > some people even disable lockdep temporarily because annotations don't > help. > > PeterZ might have opinions about that too I suspect. PeterZ is mightily confused by all of this -- also heat induced brain melt. I thought the rule was: - No allocators (alloc/free) inside raw_spinlock_t, full-stop. Why are we trying to craft an exception?
