linux-kernel - [PATCH] net: print proper warning on dst underflow

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Message-Id: <20190924090937.13001-1-Jason@zx2c4.com>
Date:   Tue, 24 Sep 2019 11:09:37 +0200
From:   "Jason A. Donenfeld" <Jason@...c4.com>
To:     netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Cc:     "Jason A. Donenfeld" <Jason@...c4.com>
Subject: [PATCH] net: print proper warning on dst underflow

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@...c4.com>
---
 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