net: page_pool: report when page pool was destroyed

Report when page pool was destroyed. Together with the inflight
/ memory use reporting this can serve as a replacement for the
warning about leaked page pools we currently print to dmesg.

Example output for a fake leaked page pool using some hacks
in netdevsim (one "live" pool, and one "leaked" on the same dev):

$ ./cli.py --no-schema --spec netlink/specs/netdev.yaml \
--dump page-pool-get
[{'id': 2, 'ifindex': 3},
{'id': 1, 'ifindex': 3, 'destroyed': 133, 'inflight': 1}]

Tested-by: Dragos Tatulea <[e-mail]>
Reviewed-by: Eric Dumazet <[e-mail]>
Acked-by: Jesper Dangaard Brouer <[e-mail]>
Signed-off-by: Jakub Kicinski <[e-mail]>
Signed-off-by: Paolo Abeni <[e-mail]>

Documentation/netlink/specs/netdev.yaml

···
         type: uint
         doc: |
           Amount of memory held by inflight pages.
+      -
+        name: detach-time
+        type: uint
+        doc: |
+          Seconds in CLOCK_BOOTTIME of when Page Pool was detached by
+          the driver. Once detached Page Pool can no longer be used to
+          allocate memory.
+          Page Pools wait for all the memory allocated from them to be freed
+          before truly disappearing. "Detached" Page Pools cannot be
+          "re-attached", they are just waiting to disappear.
+          Attribute is absent if Page Pool has not been detached, and
+          can still be used to allocate new memory.
 
 operations:
   list:
···
             - napi-id
             - inflight
             - inflight-mem
+            - detach-time
       dump:
         reply: *pp-reply
       config-cond: page-pool

include/net/page_pool/types.h

···
 	/* User-facing fields, protected by page_pools_lock */
 	struct {
 		struct hlist_node list;
+		u64 detach_time;
 		u32 napi_id;
 		u32 id;
 	} user;

include/uapi/linux/netdev.h

···
 	NETDEV_A_PAGE_POOL_NAPI_ID,
 	NETDEV_A_PAGE_POOL_INFLIGHT,
 	NETDEV_A_PAGE_POOL_INFLIGHT_MEM,
+	NETDEV_A_PAGE_POOL_DETACH_TIME,
 
 	__NETDEV_A_PAGE_POOL_MAX,
 	NETDEV_A_PAGE_POOL_MAX = (__NETDEV_A_PAGE_POOL_MAX - 1)

net/core/page_pool.c

···
 	if (!page_pool_release(pool))
 		return;
 
+	page_pool_detached(pool);
 	pool->defer_start = jiffies;
 	pool->defer_warn  = jiffies + DEFER_WARN_INTERVAL;
 

net/core/page_pool_priv.h

···
 s32 page_pool_inflight(const struct page_pool *pool, bool strict);
 
 int page_pool_list(struct page_pool *pool);
+void page_pool_detached(struct page_pool *pool);
 void page_pool_unlist(struct page_pool *pool);
 
 #endif

net/core/page_pool_user.c

···
 	    nla_put_uint(rsp, NETDEV_A_PAGE_POOL_INFLIGHT_MEM,
 			 inflight * refsz))
 		goto err_cancel;
+	if (pool->user.detach_time &&
+	    nla_put_uint(rsp, NETDEV_A_PAGE_POOL_DETACH_TIME,
+			 pool->user.detach_time))
+		goto err_cancel;
 
 	genlmsg_end(rsp, hdr);
 
···
 err_unlock:
 	mutex_unlock(&page_pools_lock);
 	return err;
+}
+
+void page_pool_detached(struct page_pool *pool)
+{
+	mutex_lock(&page_pools_lock);
+	pool->user.detach_time = ktime_get_boottime_seconds();
+	netdev_nl_page_pool_event(pool, NETDEV_CMD_PAGE_POOL_CHANGE_NTF);
+	mutex_unlock(&page_pools_lock);
 }
 
 void page_pool_unlist(struct page_pool *pool)