[PATCH v2 2/3] mm/vmalloc: fix vmalloc_dump_obj cross-zone VA lookup

[Ye Liu]

From: Ye Liu <liuye at kylinos.cn>

vmalloc_dump_obj() searches only one vmap node (addr_to_node(addr)),
but a vmalloc allocation may span multiple vmap zones.  The VA is
stored in only one node's rb-tree (addr_to_node(va_start)), so an
object pointer in a different zone than va_start maps to a different
node and the search misses.  This affects any allocation larger than
vmap_zone_size (64 KiB) on multi-CPU systems.

Iterate all vmap nodes using for_each_vmap_node, like find_vmap_area()
does, but with spin_trylock instead of spin_lock as this function can
be called from atomic dump contexts (OOM, KASAN, RCU).

Signed-off-by: Ye Liu <liuye at kylinos.cn>
---
 mm/vmalloc.c | 24 ++++++++++++++++++------
 1 file changed, 18 insertions(+), 6 deletions(-)

diff --git a/mm/vmalloc.c b/mm/vmalloc.c
index df42d8a6f058..30c610f678dc 100644
--- a/mm/vmalloc.c
+++ b/mm/vmalloc.c
@@ -5278,17 +5278,29 @@ bool vmalloc_dump_obj(void *object)
 	unsigned long nr_pages;
 
 	addr = PAGE_ALIGN_DOWN((unsigned long) object);
-	vn = addr_to_node(addr);
 
-	if (!spin_trylock(&vn->busy.lock))
-		return false;
+	/*
+	 * A vmalloc allocation may span multiple vmap zones, so the
+	 * node whose rb-tree holds the VA may differ from the node
+	 * the address maps to.  Search all nodes.  Use trylock as
+	 * this function can be called from atomic dump contexts.
+	 */
+	va = NULL;
+	for_each_vmap_node(vn) {
+		if (!spin_trylock(&vn->busy.lock))
+			continue;
+
+		va = __find_vmap_area(addr, &vn->busy.root);
+		if (va && va->vm)
+			break;
 
-	va = __find_vmap_area(addr, &vn->busy.root);
-	if (!va || !va->vm) {
 		spin_unlock(&vn->busy.lock);
-		return false;
+		va = NULL;
 	}
 
+	if (!va)
+		return false;
+
 	vm = va->vm;
 	addr = (unsigned long) vm->addr;
 	caller = vm->caller;

-- 
2.25.1