Boot stalls in v4.9.y to v5.4.y stable queues

[Guenter Roeck <linux@xxxxxxxxxxxx>]

Hi,

all stable release queues from v4.9.y up to v5.4.y have boot stall
problems. The culprit is the backport of commit d7ea0d9df2a6 ("net:
remove two BUG() from skb_checksum_help()"), specifically the following
code.

diff --git a/net/core/dev.c b/net/core/dev.c
index 47468fc5d0c9..d725ca4d4455 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -2518,11 +2518,15 @@ int skb_checksum_help(struct sk_buff *skb)
...
-       BUG_ON(offset >= skb_headlen(skb));
+       ret = -EINVAL;
        ^^^^^^^^^^^^^^
+       if (WARN_ON_ONCE(offset >= skb_headlen(skb)))
+               goto out;
+

While that works fine in the upstream kernel since ret is subsequently
always overwritten, that is not the case in older kernels. In those,
the function now always returns -EINVAL.

Guenter