[PATCH] thp+memcg-numa: fix BUG at include/linux/mm.h:370!

[Hugh Dickins <hughd@google.com>]

THP's collapse_huge_page() has an understandable but ugly difference
in when its huge page is allocated: inside if NUMA but outside if not.
It's hardly surprising that the memcg failure path forgot that, freeing
the page in the non-NUMA case, then hitting a VM_BUG_ON in get_page()
(or even worse, using the freed page).

Signed-off-by: Hugh Dickins <hughd@google.com>
---

 mm/huge_memory.c |    6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

--- 2.6.38-rc8/mm/huge_memory.c	2011-03-08 09:27:16.000000000 -0800
+++ linux/mm/huge_memory.c	2011-03-13 18:26:21.000000000 -0700
@@ -1762,6 +1762,10 @@ static void collapse_huge_page(struct mm
 #ifndef CONFIG_NUMA
 	VM_BUG_ON(!*hpage);
 	new_page = *hpage;
+	if (unlikely(mem_cgroup_newpage_charge(new_page, mm, GFP_KERNEL))) {
+		up_read(&mm->mmap_sem);
+		return;
+	}
 #else
 	VM_BUG_ON(*hpage);
 	/*
@@ -1781,12 +1785,12 @@ static void collapse_huge_page(struct mm
 		*hpage = ERR_PTR(-ENOMEM);
 		return;
 	}
-#endif
 	if (unlikely(mem_cgroup_newpage_charge(new_page, mm, GFP_KERNEL))) {
 		up_read(&mm->mmap_sem);
 		put_page(new_page);
 		return;
 	}
+#endif
 
 	/* after allocating the hugepage upgrade to mmap_sem write mode */
 	up_read(&mm->mmap_sem);

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