On Wed, Jun 19, 2019 at 3:50 PM Dave Hansen <dave.hansen@xxxxxxxxx> wrote: > > I have a bit of a grievance to file. :) > > I'm seeing "Cannot create slab..." panic()s coming from > kmem_cache_open() when trying to create memory cgroups on a Fedora > system running 5.2-rc's. The panic()s happen when failing to create > memcg-specific slabs because the memcg code passes through the > root_cache->flags, which can include SLAB_PANIC. > > I haven't tracked down the root cause yet, or where this behavior > started. But, the end-user experience is that systemd tries to create a > cgroup and ends up with a kernel panic. That's rather sad, especially > for the poor sod that's trying to debug it. > > Should memcg_create_kmem_cache() be, perhaps filtering out SLAB_PANIC > from root_cache->flags, for instance? That might make the system a bit > less likely to turn into a doorstop if and when something goes mildly > wrong. I've hacked out the panic()s and the system actually seems to > boot OK. You must be using CONFIG_SLUB and I see that in kmem_cache_open() in SLUB doing a SLAB_PANIC check. I think we should remove that altogether from SLUB as SLAB does not do this and failure in memcg kmem cache creation can and should be handled gracefully. I can send a patch to remove that check. Shakeel
