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Yet another hugepage bug

PATCH David Gibson 1 participant 1 message Jun 2, 2004

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Memory management Memory mapping
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David Gibson

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Andrew, please apply

Currently, calling msync() on a hugepage area will cause the kernel to blow up with a bad_page() (at least on ppc64, but I think the problem will exist on other archs too). The msync path attempts to walk pagetables which may not be there, or may have an unusual layout for hugepages.

Lucikly we shouldn't need to do anything for an msync on hugetlbfs beyond flushing the cache, so this patch should be sufficient to fix the problem.

mm/msync.c +9 -1
Index: working-2.6/mm/msync.c
===================================================================
@@ -11,6 +11,7 @@
 #include <linux/pagemap.h>
 #include <linux/mm.h>
 #include <linux/mman.h>
+#include <linux/hugetlb.h>
 
 #include <asm/pgtable.h>
 #include <asm/pgalloc.h>

@@ -106,6 +107,13 @@
 
 	dir = pgd_offset(vma->vm_mm, address);
 	flush_cache_range(vma, address, end);
+
+	/* For hugepages we can't go walking the page table normally,
+	 * but that's ok, hugetlbfs is memory based, so we don't need
+	 * to do anything more on an msync() */
+	if (is_vm_hugetlb_page(vma))
+		goto out;
+
 	if (address >= end)
 		BUG();
 	do {

@@ -118,7 +126,7 @@
 	 * dirty bits.
 	 */
 	flush_tlb_range(vma, end - size, end);
-
+ out:
 	spin_unlock(&vma->vm_mm->page_table_lock);
 
 	return error;
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David Gibson			| For every complex problem there is a
david AT gibson.dropbear.id.au	| solution which is simple, neat and
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