page_pool: disable direct recycling based on pool->cpuid on destroy

Now that direct recycling is performed basing on pool->cpuid when set,
memory leaks are possible:

1. A pool is destroyed.
2. Alloc cache is emptied (it's done only once).
3. pool->cpuid is still set.
4. napi_pp_put_page() does direct recycling basing on pool->cpuid.
5. Now alloc cache is not empty, but it won't ever be freed.

In order to avoid that, rewrite pool->cpuid to -1 when unlinking NAPI to
make sure no direct recycling will be possible after emptying the cache.
This involves a bit of overhead as pool->cpuid now must be accessed
via READ_ONCE() to avoid partial reads.
Rename page_pool_unlink_napi() -> page_pool_disable_direct_recycling()
to reflect what it actually does and unexport it.

Signed-off-by: Alexander Lobakin <aleksander.lobakin@intel.com>
Reviewed-by: Toke Høiland-Jørgensen <toke@redhat.com>
Link: https://lore.kernel.org/r/20240215113905.96817-1-aleksander.lobakin@intel.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

1 files changed, 7 insertions, 3 deletions

diff --git a/net/core/page_pool.c b/net/core/page_pool.c
index 89c835fcf094..e8b9399d8e32 100644
--- a/net/core/page_pool.c
+++ b/net/core/page_pool.c
@@ -949,8 +949,13 @@ void page_pool_use_xdp_mem(struct page_pool *pool, void (*disconnect)(void *),
 	pool->xdp_mem_id = mem->id;
 }
 
-void page_pool_unlink_napi(struct page_pool *pool)
+static void page_pool_disable_direct_recycling(struct page_pool *pool)
 {
+	/* Disable direct recycling based on pool->cpuid.
+	 * Paired with READ_ONCE() in napi_pp_put_page().
+	 */
+	WRITE_ONCE(pool->cpuid, -1);
+
 	if (!pool->p.napi)
 		return;
 
@@ -962,7 +967,6 @@ void page_pool_unlink_napi(struct page_pool *pool)
 
 	WRITE_ONCE(pool->p.napi, NULL);
 }
-EXPORT_SYMBOL(page_pool_unlink_napi);
 
 void page_pool_destroy(struct page_pool *pool)
 {
@@ -972,7 +976,7 @@ void page_pool_destroy(struct page_pool *pool)
 	if (!page_pool_put(pool))
 		return;
 
-	page_pool_unlink_napi(pool);
+	page_pool_disable_direct_recycling(pool);
 	page_pool_free_frag(pool);
 
 	if (!page_pool_release(pool))