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 <[email protected]>
Reviewed-by: Toke Høiland-Jørgensen <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Jakub Kicinski <[email protected]>

include/net/page_pool/types.h

@@ -210,17 +210,12 @@ struct page_pool *page_pool_create_percpu(const struct page_pool_params *params,
 struct xdp_mem_info;
 
 #ifdef CONFIG_PAGE_POOL
-void page_pool_unlink_napi(struct page_pool *pool);
 void page_pool_destroy(struct page_pool *pool);
 void page_pool_use_xdp_mem(struct page_pool *pool, void (*disconnect)(void *),
 			   struct xdp_mem_info *mem);
 void page_pool_put_page_bulk(struct page_pool *pool, void **data,
 			     int count);
 #else
-static inline void page_pool_unlink_napi(struct page_pool *pool)
-{
-}
-
 static inline void page_pool_destroy(struct page_pool *pool)
 {
 }

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))

net/core/skbuff.c

@@ -1018,7 +1018,7 @@ bool napi_pp_put_page(struct page *page, bool napi_safe)
 		unsigned int cpuid = smp_processor_id();
 
 		allow_direct = napi && READ_ONCE(napi->list_owner) == cpuid;
-		allow_direct |= (pp->cpuid == cpuid);
+		allow_direct |= READ_ONCE(pp->cpuid) == cpuid;
 	}
 
 	/* Driver set this to memory recycling info. Reset it on recycle.