Messages in this thread | | | Date | Mon, 20 Oct 2014 15:46:34 -0400 | From | Johannes Weiner <> | Subject | Re: [patch] mm: memcontrol: update mem_cgroup_page_lruvec() documentation |
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On Mon, Oct 20, 2014 at 09:12:56PM +0200, Michal Hocko wrote: > On Sun 19-10-14 11:30:16, Johannes Weiner wrote: > > 7512102cf64d ("memcg: fix GPF when cgroup removal races with last > > exit") added a pc->mem_cgroup reset into mem_cgroup_page_lruvec() to > > prevent a crash where an anon page gets uncharged on unmap, the memcg > > is released, and then the final LRU isolation on free dereferences the > > stale pc->mem_cgroup pointer. > > > > But since 0a31bc97c80c ("mm: memcontrol: rewrite uncharge API"), pages > > are only uncharged AFTER that final LRU isolation, which guarantees > > the memcg's lifetime until then. pc->mem_cgroup now only needs to be > > reset for swapcache readahead pages. > > Do we want VM_BUG_ON_PAGE(!PageSwapCache, page) into the fixup path?
While that is what we expect as of right now, it's not really a requirement for this function. Should somebody later add other page types they might trigger this assertion and scratch their head about it and wonder if they're missing some non-obvious dependency.
> > Update the comment and callsite requirements accordingly. > > > > Signed-off-by: Johannes Weiner <hannes@cmpxchg.org> > > Acked-by: Michal Hocko <mhocko@suse.cz>
Thanks!
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