From: David S. Miller Date: Wed, 31 Aug 2016 21:33:09 +0000 (-0700) Subject: Merge branch 'ppp-recursion' X-Git-Tag: v4.9-rc1~127^2~329 X-Git-Url: http://git.cascardo.info/?p=cascardo%2Flinux.git;a=commitdiff_plain;h=127661a47915f7b4c46586d02d771c5ee9a803bb Merge branch 'ppp-recursion' Guillaume Nault says: ==================== ppp: fix deadlock upon recursive xmit This series fixes the issue reported by Feng where packets looping through a ppp device makes the module deadlock: https://marc.info/?l=linux-netdev&m=147134567319038&w=2 The problem can occur on virtual interfaces (e.g. PPP over L2TP, or PPPoE on vxlan devices), when a PPP packet is routed back to the PPP interface. PPP's xmit path isn't reentrant, so patch #1 uses a per-cpu variable to detect and break recursion. Patch #2 sets the NETIF_F_LLTX flag to avoid lock inversion issues between ppp and txqueue locks. There are multiple entry points to the PPP xmit path. This series has been tested with lockdep and should address recursion issues no matter how the packet entered the path. A similar issue in L2TP is not covered by this series: l2tp_xmit_skb() also isn't reentrant, and it can be called as part of PPP's xmit path (pppol2tp_xmit()), or directly from the L2TP socket (l2tp_ppp_sendmsg()). If a packet is sent by l2tp_ppp_sendmsg() and routed to the parent PPP interface, then it's going to hit l2tp_xmit_skb() again. Breaking recursion as done in ppp_generic is not enough, because we'd still have a lock inversion issue (locking in l2tp_xmit_skb() can happen before or after locking in ppp_generic). The best approach would be to use the ip_tunnel functions and remove the socket locking in l2tp_xmit_skb(). But that'd be something for net-next. ==================== Signed-off-by: David S. Miller --- 127661a47915f7b4c46586d02d771c5ee9a803bb