On 2020-07-16 16:47:28 [+0200], Uladzislau Rezki wrote: > On Thu, Jul 16, 2020 at 04:25:37PM +0200, Sebastian Andrzej Siewior wrote: > > On 2020-07-16 11:19:13 [+0200], Uladzislau Rezki wrote: > > > Sebastian, could you please confirm that if that patch that is in > > > question fixes it? > > > > > > It would be appreciated! > > > > So that preempt disable should in terms any warnings. However I don't > > think that it is strictly needed and from scheduling point of view you > > forbid a CPU migration which might be good otherwise. > > > Please elaborate your point regarding "i do not think it is strictly needed". > > Actually i can rework the patch to remove even such preempt_enable/disable > to stay on the same CPU, but i do not see the point of doing it. > > Do you see the point? You disable preemption for what reason? It is not documented, it is not obvious - why is it required? > As for scheduling point of view. Well, there are many places when there > is a demand in memory or pages from atomic context. Also, getting a page > is not considered as a hot path in the kfree_rcu(). If you disable preemption than you assume that you wouldn't be atomic otherwise. You say that at this point it is not a hot path so if this is not *that* important why not allow preemption and allow the schedule to place you somewhere else if the scheduler decides that it is a good idea. > > Also if interrupts and everything is enabled then someone else might > > invoke kfree_rcu() from BH context for instance. > > > And what? What is a problem here, please elaborate if you see any > issues. That the kfree_rcu() caller from BH context will end up here as well, asking for a page. Sebastian
