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 @@ -6196,12 +6196,13 @@ 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 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); napi_hash_add(napi); } EXPORT_SYMBOL(netif_napi_add); --- a/net/core/netpoll.c +++ b/net/core/netpoll.c @@ -161,7 +161,7 @@ static void poll_napi(struct net_device struct napi_struct *napi; int cpu = smp_processor_id();
- list_for_each_entry(napi, &dev->napi_list, dev_list) { + list_for_each_entry_rcu(napi, &dev->napi_list, dev_list) { if (cmpxchg(&napi->poll_owner, -1, cpu) == -1) { poll_one_napi(napi); smp_store_release(&napi->poll_owner, -1);