This is a note to let you know that I've just added the patch titled net: disable netpoll on fresh napis to the 5.8-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary The filename of the patch is: net-disable-netpoll-on-fresh-napis.patch and it can be found in the queue-5.8 subdirectory. If you, or anyone else, feels it should not be added to the stable tree, please let <stable@xxxxxxxxxxxxxxx> know about it. >From foo@baz Fri Sep 11 09:06:45 AM CEST 2020 From: Jakub Kicinski <kuba@xxxxxxxxxx> Date: Wed, 26 Aug 2020 12:40:06 -0700 Subject: net: disable netpoll on fresh napis From: Jakub Kicinski <kuba@xxxxxxxxxx> [ 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@xxxxxx> Fixes: 2d8bff12699a ("netpoll: Close race condition between poll_one_napi and napi_disable") Signed-off-by: Jakub Kicinski <kuba@xxxxxxxxxx> Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> --- 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 @@ -6609,12 +6609,13 @@ void netif_napi_add(struct net_device *d netdev_err_once(dev, "%s() called with weight %d\n", __func__, weight); 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 @@ -162,7 +162,7 @@ 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); Patches currently in stable-queue which might be from kuba@xxxxxxxxxx are queue-5.8/net-disable-netpoll-on-fresh-napis.patch