Re: [PATCH] mm/hwpoison: fix race between soft_offline_page and unpoison_memory

[Wanpeng Li]

On 8/14/15 3:54 PM, Wanpeng Li wrote:
> [...]
> > OK, then I rethink of handling the race in unpoison_memory().
> >
> > Currently properly contained/hwpoisoned pages should have page refcount 1
> > (when the memory error hits LRU pages or hugetlb pages) or refcount 0
> > (when the memory error hits the buddy page.) And current unpoison_memory()
> > implicitly assumes this because otherwise the unpoisoned page has no place
> > to go and it's just leaked.
> > So to avoid the kernel panic, adding prechecks of refcount and mapcount
> > to limit the page to unpoison for only unpoisonable pages looks OK to me.
> > The page under soft offlining always has refcount >=2 and/or mapcount > 0,
> > so such pages should be filtered out.
> >
> > Here's a patch. In my testing (run soft offline stress testing then repeat
> > unpoisoning in background,) the reported (or similar) bug doesn't happen.
> > Can I have your comments?
> As page_action() prints out page maybe still referenced by some users,
> however, PageHWPoison has already set. So you will leak many poison pages.

Anyway, the bug is still there.

[  944.387559] BUG: Bad page state in process expr  pfn:591e3
[  944.393053] page:ffffea00016478c0 count:-1 mapcount:0 
mapping:          (null) index:0x2
[  944.401147] flags: 0x1fffff80000000()
[  944.404819] page dumped because: nonzero _count

Regards,
Wanpeng Li
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