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[24.6.151.244]) by smtp.gmail.com with ESMTPSA id 98e67ed59e1d1-2e9a5f52cacsm10867477a91.6.2024.11.12.09.12.30 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 12 Nov 2024 09:12:32 -0800 (PST) Date: Tue, 12 Nov 2024 09:12:29 -0800 From: Joe Damato To: Paolo Abeni Cc: netdev@vger.kernel.org, mkarsten@uwaterloo.ca, skhawaja@google.com, sdf@fomichev.me, bjorn@rivosinc.com, amritha.nambiar@intel.com, sridhar.samudrala@intel.com, willemdebruijn.kernel@gmail.com, edumazet@google.com, Jakub Kicinski , Donald Hunter , "David S. Miller" , Jesper Dangaard Brouer , Mina Almasry , Xuan Zhuo , open list Subject: Re: [net-next v6 6/9] netdev-genl: Support setting per-NAPI config values Message-ID: Mail-Followup-To: Joe Damato , Paolo Abeni , netdev@vger.kernel.org, mkarsten@uwaterloo.ca, skhawaja@google.com, sdf@fomichev.me, bjorn@rivosinc.com, amritha.nambiar@intel.com, sridhar.samudrala@intel.com, willemdebruijn.kernel@gmail.com, edumazet@google.com, Jakub Kicinski , Donald Hunter , "David S. Miller" , Jesper Dangaard Brouer , Mina Almasry , Xuan Zhuo , open list References: <20241011184527.16393-1-jdamato@fastly.com> <20241011184527.16393-7-jdamato@fastly.com> <719083c2-e277-447b-b6ea-ca3acb293a03@redhat.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <719083c2-e277-447b-b6ea-ca3acb293a03@redhat.com> On Tue, Nov 12, 2024 at 10:17:40AM +0100, Paolo Abeni wrote: > On 10/11/24 20:45, Joe Damato wrote: > > +int netdev_nl_napi_set_doit(struct sk_buff *skb, struct genl_info *info) > > +{ > > + struct napi_struct *napi; > > + unsigned int napi_id; > > + int err; > > + > > + if (GENL_REQ_ATTR_CHECK(info, NETDEV_A_NAPI_ID)) > > + return -EINVAL; > > + > > + napi_id = nla_get_u32(info->attrs[NETDEV_A_NAPI_ID]); > > + > > + rtnl_lock(); > > + > > + napi = napi_by_id(napi_id); > > AFAICS the above causes a RCU splat in the selftests: > > https://netdev-3.bots.linux.dev/vmksft-net-dbg/results/856342/61-busy-poll-test-sh/stderr > > because napi_by_id() only checks for the RCU lock. > > Could you please have a look? Thanks for letting me know. I rebuilt my kernel with CONFIG_PROVE_RCU_LIST and a couple other debugging options and I was able to reproduce the splat you mentioned. I took a look and it looks like there might be two things: - netdev_nl_napi_set_doit needs to call rcu_read_lock / rcu_read_unlock, which would be a Fixes on the commit in the series just merged, and - netdev_nl_napi_get_doit also has the same issue and should be fixed in a separate commit with its own fixes tag. If that sounds right to you, I'll propose a short series of 2 patches, 1 to fix each. Let me know if that sounds OK? In the meantime, I'm rebuilding a kernel now to ensure my proposed fix fixes the splat.