On 21.10.2014 00:50, Oleg Nesterov wrote: > On 10/21, Kirill Tkhai wrote: >> >> I think generic helper is a good idea. The prototype looks OK. >> >> But I'm a little doubt about retry loop. If this helper is generic and >> one day it may move to ./include directory, > > Well, if we add a generic helper I think it should be exported even if > it has a single caller. But I agree this probably needs a justification > too. > >> isn't there a probability >> people will use it wrong? This loop may bring delays or something bad. > > Yes, I thought about livelock too. OK, we can remove it, just > s/goto retry/return NULL/. Or, perhaps better, return ERR_PTR(-EAGAIN) > so that the caller can know that retry is possible. > > I do not really mind, and we can reconsider this later. And I will not > argue if you prefer to add the rq->curr specific hack (like your patch > does). > >> And since we still depends on RCU, I'd suggest to add its lockdep assert. > > Agreed. > > Let me explain what I personally dislike in v3: > > - I think that we do not have enough reasons for > SLAB_DESTROY_BY_RCU. This is the serious change. > > probe_kernel_read() looks better to me, and hopefully > IS_ENABLED(DEBUG_PAGEALLOC) can make it conditional. > > - PF_EXITING was fine in task_numa_compare(), but if we > move this logic into a helper (even if it is not exported) > then I think we need a more specific check. sighand == NULL > looks better to me because it clearly connects to > release_task() which makes this task_struct "rcu-unsafe". > > - Again, perhaps we should start we a simple and stupid fix. > We can do get_task_struct() under rq->lock or, if nothing > else, just > > raw_spin_lock_irq(&rq->lock); > cur = rq->curr; > if (is_idle_task(cur) || (cur->flags & PF_EXITING)) > cur = NULL; > raw_spin_unlock_irq(&rq->lock); > > Either way, I hope you will send v4 ;)
No, I won't send. Please do this. Your idea and your patch is almost ready. Thanks :) > But probably you should wait for for Peter's opinion first. Yeah. Kirill -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
