netdev - [RFC -next 0/3] Re: [PATCH net 1/2] net: disable netpoll on fresh napis

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Message-Id: <20200827223250.2045503-1-kuba@kernel.org>
Date:   Thu, 27 Aug 2020 15:32:47 -0700
From:   Jakub Kicinski <kuba@...nel.org>
To:     eric.dumazet@...il.com
Cc:     davem@...emloft.net, netdev@...r.kernel.org, kernel-team@...com,
        Jakub Kicinski <kuba@...nel.org>
Subject: [RFC -next 0/3] Re: [PATCH net 1/2] net: disable netpoll on fresh napis

On Thu, 27 Aug 2020 10:47:53 -0700 Jakub Kicinski wrote:
> > Oh, I really thought list_for_each_entry_rcu() was only checking standard rcu.
> > 
> > I might have been confused because we do have hlist_for_each_entry_rcu_bh() helper.
> > 
> > Anyway, when looking at the patch I was not at ease because we do not have proper
> > rcu grace period when a napi is removed from dev->napi_list. A driver might
> > free the napi struct right after calling netif_napi_del()  
> 
> Ugh, you're right. I didn't look closely enough at netif_napi_del():
> 
> 	if (napi_hash_del(napi))
> 		synchronize_net();
> 	list_del_init(&napi->dev_list);
> 
> Looks like I can reorder these.. and perhaps make all dev->napi_list
> accesses RCU, for netpoll?

So I had a look and looks like some reshuffling may be required
to get out of this pickle. The objective is for drivers to observe
RCU grace period after netif_napi_del() not just napi_hash_del().

Sending as RFC because IDK if the churn vs improvement ratio
is acceptable here.

Jakub Kicinski (3):
  net: remove napi_hash_del() from driver-facing API
  net: manage napi add/del idempotence explicitly
  net: make sure napi_list is safe for RCU traversal

 .../net/ethernet/broadcom/bnx2x/bnx2x_cmn.h   |  8 ++---
 drivers/net/ethernet/broadcom/bnxt/bnxt.c     |  5 ++-
 drivers/net/ethernet/cisco/enic/enic_main.c   | 12 ++++---
 drivers/net/ethernet/intel/ixgbe/ixgbe_lib.c  |  4 +--
 .../net/ethernet/myricom/myri10ge/myri10ge.c  |  5 ++-
 drivers/net/veth.c                            |  3 +-
 drivers/net/virtio_net.c                      |  7 ++--
 include/linux/netdevice.h                     | 36 +++++++++----------
 net/core/dev.c                                | 32 ++++++++---------
 net/core/netpoll.c                            |  2 +-
 10 files changed, 55 insertions(+), 59 deletions(-)

-- 
2.26.2