[PATCH] mm: Make vb_alloc() more foolproof

[Jan Kara <jack@suse.cz>]

If someone calls vb_alloc() (or vm_map_ram() for that matter) to allocate
0 bytes (0 pages), get_order() returns BITS_PER_LONG - PAGE_CACHE_SHIFT
and interesting stuff happens. So make debugging such problems easier and
warn about 0-size allocation.

Signed-off-by: Jan Kara <jack@suse.cz>
---
 mm/vmalloc.c |    9 +++++++++
 1 files changed, 9 insertions(+), 0 deletions(-)

diff --git a/mm/vmalloc.c b/mm/vmalloc.c
index 2aad499..bebee70 100644
--- a/mm/vmalloc.c
+++ b/mm/vmalloc.c
@@ -904,6 +904,15 @@ static void *vb_alloc(unsigned long size, gfp_t gfp_mask)
 
 	BUG_ON(size & ~PAGE_MASK);
 	BUG_ON(size > PAGE_SIZE*VMAP_MAX_ALLOC);
+	if (size == 0) {
+		/*
+		 * Allocating 0 bytes isn't what caller wants since
+		 * get_order(0) returns funny result. Just warn and terminate
+		 * early.
+		 */
+		WARN_ON(1);
+		return NULL;
+	}
 	order = get_order(size);
 
 again:
-- 
1.7.1

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