[PATCH] net: print proper warning on dst underflow

[Jason A. Donenfeld]

Proper warnings with stack traces make it much easier to figure out
what's doing the double free and create more meaningful bug reports from
users.

Signed-off-by: Jason A. Donenfeld <Jason@xxxxxxxxx>
---
 net/core/dst.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/net/core/dst.c b/net/core/dst.c
index 1325316d9eab..193af526e908 100644
--- a/net/core/dst.c
+++ b/net/core/dst.c
@@ -172,7 +172,7 @@ void dst_release(struct dst_entry *dst)
 		int newrefcnt;
 
 		newrefcnt = atomic_dec_return(&dst->__refcnt);
-		if (unlikely(newrefcnt < 0))
+		if (WARN_ONCE(newrefcnt < 0, "dst_release underflow"))
 			net_warn_ratelimited("%s: dst:%p refcnt:%d\n",
 					     __func__, dst, newrefcnt);
 		if (!newrefcnt)
@@ -187,7 +187,7 @@ void dst_release_immediate(struct dst_entry *dst)
 		int newrefcnt;
 
 		newrefcnt = atomic_dec_return(&dst->__refcnt);
-		if (unlikely(newrefcnt < 0))
+		if (WARN_ONCE(newrefcnt < 0, "dst_release_immediate underflow"))
 			net_warn_ratelimited("%s: dst:%p refcnt:%d\n",
 					     __func__, dst, newrefcnt);
 		if (!newrefcnt)
-- 
2.21.0