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Date: Tue, 8 Dec 2020 16:17:37 -0800 From: Jakub Kicinski <kuba@...nel.org> To: Vladimir Oltean <vladimir.oltean@....com> Cc: "David S . Miller" <davem@...emloft.net>, "netdev@...r.kernel.org" <netdev@...r.kernel.org>, Andrew Lunn <andrew@...n.ch>, Florian Fainelli <f.fainelli@...il.com>, Paul Gortmaker <paul.gortmaker@...driver.com>, Pablo Neira Ayuso <pablo@...filter.org>, Jiri Benc <jbenc@...hat.com>, Cong Wang <xiyou.wangcong@...il.com>, Jamal Hadi Salim <jhs@...atatu.com>, Stephen Hemminger <stephen@...workplumber.org>, Eric Dumazet <edumazet@...gle.com>, George McCollister <george.mccollister@...il.com>, Oleksij Rempel <o.rempel@...gutronix.de>, Jay Vosburgh <j.vosburgh@...il.com>, Veaceslav Falico <vfalico@...il.com>, Andy Gospodarek <andy@...yhouse.net> Subject: Re: [RFC PATCH net-next 05/13] net: bonding: hold the netdev lists lock when retrieving device statistics On Wed, 9 Dec 2020 00:03:56 +0000 Vladimir Oltean wrote: > On Tue, Dec 08, 2020 at 03:57:44PM -0800, Jakub Kicinski wrote: > > On Mon, 7 Dec 2020 01:00:40 +0000 Vladimir Oltean wrote: > > > - ensuring through convention that user space always takes > > > net->netdev_lists_lock when calling dev_get_stats, and documenting > > > that, and therefore making it unnecessary to lock in bonding. > > > > This seems like the better option to me. Makes the locking rules pretty > > clear. > > It is non-obvious to me that top-level callers of dev_get_stats should > hold a lock as specific as the one protecting the lists of network > interfaces. In the vast majority of implementations of dev_get_stats, > that lock would not actually protect anything, which would lead into > just one more lock that is used for more than it should be. In my tree I > had actually already switched over to mutex_lock_nested. Nonetheless, I > am still open if you want to make the case that simplicity should prevail > over specificity. What are the locking rules you have in mind then? Caller may hold RTNL or ifc mutex? > But in that case, maybe we should just keep on using the RTNL mutex. That's a wasted opportunity, RTNL lock is pretty busy.
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