Messages in this thread | | | Date | Fri, 4 Oct 2019 14:57:01 +0200 | From | Michal Hocko <> | Subject | Re: [PATCH v2] mm/slub: fix a deadlock in show_slab_objects() |
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On Fri 04-10-19 08:31:49, Qian Cai wrote: > Long time ago, there fixed a similar deadlock in show_slab_objects() > [1]. However, it is apparently due to the commits like 01fb58bcba63 > ("slab: remove synchronous synchronize_sched() from memcg cache > deactivation path") and 03afc0e25f7f ("slab: get_online_mems for > kmem_cache_{create,destroy,shrink}"), this kind of deadlock is back by > just reading files in /sys/kernel/slab which will generate a lockdep > splat below. > > Since the "mem_hotplug_lock" here is only to obtain a stable online node > mask while racing with NUMA node hotplug, in the worst case, the results > may me miscalculated while doing NUMA node hotplug, but they shall be > corrected by later reads of the same files.
I think it is important to mention that this doesn't expose the show_slab_objects to use-after-free. There is only a single path that might really race here and that is the slab hotplug notifier callback __kmem_cache_shrink (via slab_mem_going_offline_callback) but that path doesn't really destroy kmem_cache_node data structures.
Thanks! -- Michal Hocko SUSE Labs
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