On Fri 20-09-19 17:10:42, Andrew Morton wrote: > On Sat, 20 Jul 2019 20:29:23 +0900 Tetsuo Handa <penguin-kernel@xxxxxxxxxxxxxxxxxxx> wrote: > > > > > > >> ) under RCU and this patch is one of them (except that we can't remove > > >> printk() for dump_tasks() case). > > > > > > No, this one adds a complexity for something that is not clearly a huge > > > win or the win is not explained properly. > > > > > > > The win is already explained properly by the past commits. Avoiding RCU stalls > > (even without slow consoles) is a clear win. The duration of RCU stall avoided > > by this patch is roughly the same with commit b2b469939e934587. > > > > We haven't succeeded making printk() asynchronous (and potentially we won't > > succeed making printk() asynchronous because we need synchronous printk() > > when something critical is undergoing outside of out_of_memory()). Thus, > > bringing printk() to outside of RCU section is a clear win we can make for now. > > It's actually not a complex patch and moving all that printing outside > the rcu section makes sense. So I'll sit on the patch for a few more > days but am inclined to send it upstream. Look, I am quite tired of arguing about this and other changes following the similar pattern. In short a problematic code is shuffled around and pretend to solve some problem. In this particular case it is a RCU stall which in itself is not a fatal condition. Sure it sucks and the primary reason is that printk can take way too long. This is something that is currently a WIP to be address. What is more important though there is no sign of any _real world_ workload that would require a quick workaround to justify a hacky stop gap solution. So again, why do we want to add more code for something which is not clear to be a real life problem and that will add a maintenance burden for future? -- Michal Hocko SUSE Labs
