Messages in this thread | | | Date | Mon, 21 Aug 2017 09:02:18 -0400 | From | Johannes Weiner <> | Subject | Re: kernel panic on null pointer on page->mem_cgroup |
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On Thu, Aug 10, 2017 at 01:56:05PM +0200, Michal Hocko wrote: > On Wed 09-08-17 14:38:25, Johannes Weiner wrote: > > The issue is that writeback doesn't hold a page reference and the page > > might get freed after PG_writeback is cleared (and the mapping is > > unlocked) in test_clear_page_writeback(). The stat functions looking > > up the page's node or zone are safe, as those attributes are static > > across allocation and free cycles. But page->mem_cgroup is not, and it > > will get cleared if we race with truncation or migration. > > Is there anything that prevents us from holding a reference on a page > under writeback?
Hm, I'm hesitant to add redundant life-time management to the page there just for memcg, which is not always configured in.
Pinning the memcg instead is slightly more complex, but IMO has the complexity in a preferrable place.
Would you agree?
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