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Wed, 16 Mar 2022 20:46:49 +0000 Received: from SN6PR11MB3229.namprd11.prod.outlook.com ([fe80::d484:c3ff:3689:fe81]) by SN6PR11MB3229.namprd11.prod.outlook.com ([fe80::d484:c3ff:3689:fe81%6]) with mapi id 15.20.5061.028; Wed, 16 Mar 2022 20:46:49 +0000 Message-ID: <1e22c10f-1814-10fc-b0bd-e086eccf3e71@intel.com> Date: Wed, 16 Mar 2022 13:46:46 -0700 User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:91.0) Gecko/20100101 Thunderbird/91.7.0 Subject: Re: [PATCH net 1/3] ice: fix NULL pointer dereference in ice_update_vsi_tx_ring_stats() Content-Language: en-US To: Alexander Duyck CC: "kuba@kernel.org" , lkp , "Karlsson, Magnus" , "davem@davemloft.net" , "Lobakin, Alexandr" , "Fijalkowski, Maciej" , "dan.carpenter@oracle.com" , "pabeni@redhat.com" , "netdev@vger.kernel.org" , "G, GurucharanX" References: <20220315211225.2923496-1-anthony.l.nguyen@intel.com> <20220315211225.2923496-2-anthony.l.nguyen@intel.com> <20220315202941.64319c5e@kicinski-fedora-pc1c0hjn.dhcp.thefacebook.com> From: Tony Nguyen In-Reply-To: Content-Type: text/plain; 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>>>> >>>> ring = READ_ONCE(rings[i]); >>> Not really related to this patch but why is there a read_once() here? >>> Aren't stats read under rtnl_lock? What is this protecting against? >> It looks like it was based on a patch from i40e [1]. From the commit, I >> gather this is the reason: >> >> "Previously the stats were 64 bit but highly racy due to the fact that >> 64 bit transactions are not atomic on 32 bit systems." >> >> Thanks, >> >> Tony >> >> [1] >> https://git.kernel.org/pub/scm/linux/kernel/git/netdev/net-next.git/commit/?id=980e9b1186424fa3eb766d59fc91003d0ed1ed6a >> >> >> (Resending as some non-text formatting snuck in to my reply. Sorry for >> the spam) > Actually the rcu locking and READ_ONCE has to do with the fact that > the driver code for the igb/ixgbe/i40e driver had a bunch of code that > could kick in from the sysfs and/or PCIe paths that would start > tearing things down without necessarily holding the rtnl_lock as it > should have. > > It might make sense to reevaluate the usage of the READ_ONCE and rcu > locking to determine if it is actually needed since much of that is a > hold over from when we were doing this in the watchdog and not while > holding the rtnl_lock in the stats call. Thanks for clarifying Alex. I'll ask the teams to look into this.