[PATCH] mm: prep_zero_page() in irq is a bug

prep_zero_page() uses KM_USER0 and hence may not be used from IRQ context, at
least for highmem pages.

Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Cc: Christoph Lameter <christoph@lameter.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

1 files changed, 5 insertions, 0 deletions

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index bdff85899638..ed91684cb1f5 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -217,6 +217,11 @@ static inline void prep_zero_page(struct page *page, int order, gfp_t gfp_flags)
         int i;
 
         BUG_ON((gfp_flags & (__GFP_WAIT | __GFP_HIGHMEM)) == __GFP_HIGHMEM);
+        /*
+         * clear_highpage() will use KM_USER0, so it's a bug to use __GFP_ZERO
+         * and __GFP_HIGHMEM from hard or soft interrupt context.
+         */
+        BUG_ON((gfp_flags & __GFP_HIGHMEM) && in_interrupt());
         for (i = 0; i < (1 << order); i++)
                 clear_highpage(page + i);
 }