[PATCH 4.4 62/62] net: disable netpoll on fresh napis

Greg Kroah-Hartman
2020-09-11T17:27:10Z

From: Jakub Kicinski <kuba@kernel.org>

[ Upstream commit 96e97bc07e90f175a8980a22827faf702ca4cb30 ]

napi_disable() makes sure to set the NAPI_STATE_NPSVC bit to prevent
netpoll from accessing rings before init is complete. However, the
same is not done for fresh napi instances in netif_napi_add(),
even though we expect NAPI instances to be added as disabled.

This causes crashes during driver reconfiguration (enabling XDP,
changing the channel count) - if there is any printk() after
netif_napi_add() but before napi_enable().

To ensure memory ordering is correct we need to use RCU accessors.

Reported-by: Rob Sherwood <rsher@fb.com>
Fixes: 2d8bff12699a ("netpoll: Close race condition between poll_one_napi and napi_disable")
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
net/core/dev.c | 3 ++-
net/core/netpoll.c | 2 +-
2 files changed, 3 insertions(+), 2 deletions(-)

--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -4849,13 +4849,14 @@ void netif_napi_add(struct net_device *d
pr_err_once("netif_napi_add() called with weight %d on device %s\n",
weight, dev->name);
napi->weight = weight;
- list_add(&napi->dev_list, &dev->napi_list);
napi->dev = dev;
#ifdef CONFIG_NETPOLL
spin_lock_init(&napi->poll_lock);
napi->poll_owner = -1;
#endif
set_bit(NAPI_STATE_SCHED, &napi->state);
+ set_bit(NAPI_STATE_NPSVC, &napi->state);
+ list_add_rcu(&napi->dev_list, &dev->napi_list);
}
EXPORT_SYMBOL(netif_napi_add);

--- a/net/core/netpoll.c
+++ b/net/core/netpoll.c
@@ -178,7 +178,7 @@ static void poll_napi(struct net_device
{
struct napi_struct *napi;

- list_for_each_entry(napi, &dev->napi_list, dev_list) {
+ list_for_each_entry_rcu(napi, &dev->napi_list, dev_list) {
if (napi->poll_owner != smp_processor_id() &&
spin_trylock(&napi->poll_lock)) {
poll_one_napi(napi);