Messages in this thread | | | Subject | Re: [PATCH v2] mm/page_isolation: fix a deadlock with printk() | From | David Hildenbrand <> | Date | Thu, 10 Oct 2019 20:59:35 +0200 |
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On 10.10.19 20:06, Michal Hocko wrote: > On Thu 10-10-19 13:48:06, Qian Cai wrote: >> On Thu, 2019-10-10 at 19:30 +0200, Michal Hocko wrote: >>> On Thu 10-10-19 10:47:38, Qian Cai wrote: >>>> On Thu, 2019-10-10 at 16:18 +0200, Michal Hocko wrote: >>>>> On Thu 10-10-19 09:11:52, Qian Cai wrote: >>>>>> On Thu, 2019-10-10 at 12:59 +0200, Michal Hocko wrote: >>>>>>> On Thu 10-10-19 05:01:44, Qian Cai wrote: >>>>>>>> >>>>>>>> >>>>>>>>> On Oct 9, 2019, at 12:23 PM, Michal Hocko <mhocko@kernel.org> wrote: >>>>>>>>> >>>>>>>>> If this was only about the memory offline code then I would agree. But >>>>>>>>> we are talking about any printk from the zone->lock context and that is >>>>>>>>> a bigger deal. Besides that it is quite natural that the printk code >>>>>>>>> should be more universal and allow to be also called from the MM >>>>>>>>> contexts as much as possible. If there is any really strong reason this >>>>>>>>> is not possible then it should be documented at least. >>>>>>>> >>>>>>>> Where is the best place to document this? I am thinking about under >>>>>>>> the “struct zone” definition’s lock field in mmzone.h. >>>>>>> >>>>>>> I am not sure TBH and I do not think we have reached the state where >>>>>>> this would be the only way forward. >>>>>> >>>>>> How about I revised the changelog to focus on memory offline rather than making >>>>>> a rule that nobody should call printk() with zone->lock held? >>>>> >>>>> If you are to remove the CONFIG_DEBUG_VM printk then I am all for it. I >>>>> am still not convinced that fiddling with dump_page in the isolation >>>>> code is justified though. >>>> >>>> No, dump_page() there has to be fixed together for memory offline to be useful. >>>> What's the other options it has here? >>> >>> I would really prefer to not repeat myself >>> http://lkml.kernel.org/r/20191010074049.GD18412@dhcp22.suse.cz >> >> Care to elaborate what does that mean? I am confused on if you finally agree on >> no printk() while held zone->lock or not. You said "If there is absolutely >> no way around that then we might have to bite a bullet and consider some >> of MM locks a land of no printk." which makes me think you agreed, but your >> stance from the last reply seems you were opposite to it. > > I really do mean that the first step is to remove the dependency from > the printk and remove any allocation from the console callbacks. If that > turns out to be infeasible then we have to bite the bullet and think of > a way to drop all printks from all locks that participate in an atomic > allocation requests. >
I second that and dropping the useless printk() as Michal mentioned. I would beg to not uglify the offlining/isolation code with __nolock variants or dropping locks somewhere down in a function. If everything fails, I rather want to see the prinkt's gone or returning details in a struct back to the caller, that can print it instead.
e.g.,
struct unmovable_page_info { const char *reason; struct page *page; ... };
You should get the idea.
--
Thanks,
David / dhildenb
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