[PATCH v3 1/2] mm/vmalloc: fix vmalloc_dump_obj address alignment for last-page lookups

[Ye Liu]

From: Ye Liu <liuye at kylinos.cn>

vmalloc_dump_obj() uses PAGE_ALIGN() to normalize the input address
before looking it up in the per-node busy tree.  PAGE_ALIGN() rounds
up, which can push an address in the last page of a vmalloc allocation
to va_end -- outside the [va_start, va_end) range that
__find_vmap_area() searches.  This causes the lookup to miss the VA
and return false, degrading diagnostic output in OOM dumps and KASAN
reports to the less informative "vmalloc memory" fallback.

The upward alignment can also change the addr_to_node() mapping when
the page boundary crosses a vmap zone boundary, causing the search to
hit the wrong node entirely.

Use PAGE_ALIGN_DOWN() instead, which rounds down to the page
containing the address.  This keeps the address within the VA range
and preserves the correct node mapping.

Signed-off-by: Ye Liu <liuye at kylinos.cn>
Reviewed-by: Uladzislau Rezki (Sony) <urezki at gmail.com>
---
 mm/vmalloc.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/mm/vmalloc.c b/mm/vmalloc.c
index 859e6d2d57a3..df42d8a6f058 100644
--- a/mm/vmalloc.c
+++ b/mm/vmalloc.c
@@ -5277,7 +5277,7 @@ bool vmalloc_dump_obj(void *object)
 	unsigned long addr;
 	unsigned long nr_pages;
 
-	addr = PAGE_ALIGN((unsigned long) object);
+	addr = PAGE_ALIGN_DOWN((unsigned long) object);
 	vn = addr_to_node(addr);
 
 	if (!spin_trylock(&vn->busy.lock))

-- 
2.25.1