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
