Re: [syzbot] INFO: rcu detected stall in syscall_exit_to_user_mode (2)

[Hillf Danton <hdanton@sina.com>]

On Sun, 25 Dec 2022 17:42:37 -0800
> syzbot has found a reproducer for the following issue on:
> 
> HEAD commit:    72a85e2b0a1e Merge tag 'spi-fix-v6.2-rc1' of git://git.ker..
> git tree:       upstream
> C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=12569d7f880000

#syz test https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git  master

--- x/drivers/media/rc/imon.c
+++ y/drivers/media/rc/imon.c
@@ -1758,6 +1758,7 @@ static void usb_rx_callback_intf0(struct
 
 	switch (urb->status) {
 	case -ENOENT:		/* usbcore unlink successful! */
+	case -EPROTO:
 		return;
 
 	case -ESHUTDOWN:	/* transport endpoint was shut down */
--- x/net/batman-adv/network-coding.c
+++ y/net/batman-adv/network-coding.c
@@ -397,6 +397,7 @@ static void batadv_nc_purge_orig_hash(st
 	struct hlist_head *head;
 	struct batadv_orig_node *orig_node;
 	u32 i;
+	int loop = 0;
 
 	if (!hash)
 		return;
@@ -406,9 +407,14 @@ static void batadv_nc_purge_orig_hash(st
 		head = &hash->table[i];
 
 		rcu_read_lock();
-		hlist_for_each_entry_rcu(orig_node, head, hash_entry)
+		hlist_for_each_entry_rcu(orig_node, head, hash_entry) {
 			batadv_nc_purge_orig(bat_priv, orig_node,
 					     batadv_nc_to_purge_nc_node);
+			if (++loop > 20) {
+				rcu_read_unlock();
+				return;
+			}
+		}
 		rcu_read_unlock();
 	}
 }
@@ -433,6 +439,7 @@ static void batadv_nc_purge_paths(struct
 	struct batadv_nc_path *nc_path;
 	spinlock_t *lock; /* Protects lists in hash */
 	u32 i;
+	int loop = 0;
 
 	for (i = 0; i < hash->size; i++) {
 		head = &hash->table[i];
@@ -441,6 +448,10 @@ static void batadv_nc_purge_paths(struct
 		/* For each nc_path in this bin */
 		spin_lock_bh(lock);
 		hlist_for_each_entry_safe(nc_path, node_tmp, head, hash_entry) {
+			if (++loop > 20) {
+				spin_unlock_bh(lock);
+				return;
+			}
 			/* if an helper function has been passed as parameter,
 			 * ask it if the entry has to be purged or not
 			 */
@@ -675,6 +686,7 @@ batadv_nc_process_nc_paths(struct batadv
 	struct batadv_nc_path *nc_path;
 	bool ret;
 	int i;
+	int loop = 0;
 
 	if (!hash)
 		return;
@@ -686,6 +698,10 @@ batadv_nc_process_nc_paths(struct batadv
 		/* Loop coding paths */
 		rcu_read_lock();
 		hlist_for_each_entry_rcu(nc_path, head, hash_entry) {
+			if (++loop > 20) {
+				rcu_read_unlock();
+				return;
+			}
 			/* Loop packets */
 			spin_lock_bh(&nc_path->packet_list_lock);
 			list_for_each_entry_safe(nc_packet, nc_packet_tmp,
--