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mm: don't dereference struct page fields of invalid pages

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The VM_BUG_ON() check in move_freepages() checks whether the node id of
a page matches the node id of its zone.  However, it does this before
having checked whether the struct page pointer refers to a valid struct
page to begin with.  This is guaranteed in most cases, but may not be
the case if CONFIG_HOLES_IN_ZONE=y.

So reorder the VM_BUG_ON() with the pfn_valid_within() check.

Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: Ard Biesheuvel <[email protected]>
Acked-by: Will Deacon <[email protected]>
Cc: Catalin Marinas <[email protected]>
Cc: Hanjun Guo <[email protected]>
Cc: Yisheng Xie <[email protected]>
Cc: Robert Richter <[email protected]>
Cc: James Morse <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>
This commit is contained in:
Ard Biesheuvel 2017-01-10 16:58:00 -08:00 • committed by Linus Torvalds
commit f073bdc517
1 changed files with 3 additions and 3 deletions
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6
mm/page_alloc.c
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@ -1864,14 +1864,14 @@ int move_freepages(struct zone *zone,
#endif
for (page = start_page; page <= end_page;) {
/* Make sure we are not inadvertently changing nodes */
VM_BUG_ON_PAGE(page_to_nid(page) != zone_to_nid(zone), page);
if (!pfn_valid_within(page_to_pfn(page))) {
page++;
continue;
}
/* Make sure we are not inadvertently changing nodes */
VM_BUG_ON_PAGE(page_to_nid(page) != zone_to_nid(zone), page);
if (!PageBuddy(page)) {
page++;
continue;