[PATCH 6.12.y] mm/vmalloc: take vmap_purge_lock in shrinker

[Sasha Levin <sashal@kernel.org>]

From: "Uladzislau Rezki (Sony)" <urezki@gmail.com>

[ Upstream commit ec05f51f1e65bce95528543eb73fda56fd201d94 ]

decay_va_pool_node() can be invoked concurrently from two paths:
__purge_vmap_area_lazy() when pools are being purged, and the shrinker via
vmap_node_shrink_scan().

However, decay_va_pool_node() is not safe to run concurrently, and the
shrinker path currently lacks serialization, leading to races and possible
leaks.

Protect decay_va_pool_node() by taking vmap_purge_lock in the shrinker
path to ensure serialization with purge users.

Link: https://lore.kernel.org/20260413192646.14683-1-urezki@gmail.com
Fixes: 7679ba6b36db ("mm: vmalloc: add a shrinker to drain vmap pools")
Signed-off-by: Uladzislau Rezki (Sony) <urezki@gmail.com>
Reviewed-by: Baoquan He <baoquan.he@linux.dev>
Cc: chenyichong <chenyichong@uniontech.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
[ kept index-based loop instead of for_each_vmap_node() helper ]
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 mm/vmalloc.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/mm/vmalloc.c b/mm/vmalloc.c
index 1d2262fb54185..d4a42980b4d02 100644
--- a/mm/vmalloc.c
+++ b/mm/vmalloc.c
@@ -5204,6 +5204,7 @@ vmap_node_shrink_scan(struct shrinker *shrink, struct shrink_control *sc)
 {
 	int i;
 
+	guard(mutex)(&vmap_purge_lock);
 	for (i = 0; i < nr_vmap_nodes; i++)
 		decay_va_pool_node(&vmap_nodes[i], true);
 
-- 
2.53.0