From: Eric Dumazet <edumazet@google.com>
To: Vladimir Oltean <olteanv@gmail.com>
Cc: Stephen Hemminger <stephen@networkplumber.org>,
Eric Dumazet <eric.dumazet@gmail.com>,
Jakub Kicinski <kuba@kernel.org>, netdev <netdev@vger.kernel.org>,
Paul Gortmaker <paul.gortmaker@windriver.com>,
Jiri Benc <jbenc@redhat.com>, Or Gerlitz <ogerlitz@mellanox.com>,
Cong Wang <xiyou.wangcong@gmail.com>,
Jamal Hadi Salim <jhs@mojatatu.com>, Andrew Lunn <andrew@lunn.ch>,
Florian Fainelli <f.fainelli@gmail.com>
Subject: Re: Correct usage of dev_base_lock in 2020
Date: Mon, 30 Nov 2020 22:46:00 +0100 [thread overview]
Message-ID: <CANn89iJGA8qWBJ97nnNGNOuLNUYF5WPnL+qi722KYCD7kvKyCg@mail.gmail.com> (raw)
In-Reply-To: <20201130211158.37ay2uvdwcnegw45@skbuf>
On Mon, Nov 30, 2020 at 10:12 PM Vladimir Oltean <olteanv@gmail.com> wrote:
>
> On Mon, Nov 30, 2020 at 10:00:16PM +0100, Eric Dumazet wrote:
> > On Mon, Nov 30, 2020 at 9:50 PM Vladimir Oltean <olteanv@gmail.com> wrote:
> > >
> > > On Mon, Nov 30, 2020 at 09:43:01PM +0100, Eric Dumazet wrote:
> > > > Understood, but really dev_base_lock can only be removed _after_ we
> > > > convert all usages to something else (mutex based, and preferably not
> > > > the global RTNL)
> > >
> > > Sure.
> > > A large part of getting rid of dev_base_lock seems to be just:
> > > - deleting the bogus usage from mlx4 infiniband and friends
> > > - converting procfs, sysfs and friends to netdev_lists_mutex
> > > - renaming whatever is left into something related to the RFC 2863
> > > operstate.
> > >
> > > > Focusing on dev_base_lock seems a distraction really.
> > >
> > > Maybe.
> > > But it's going to be awkward to explain in words what the locking rules
> > > are, when the read side can take optionally the dev_base_lock, RCU, or
> > > netdev_lists_lock, and the write side can take optionally the dev_base_lock,
> > > RTNL, or netdev_lists_lock. Not to mention that anybody grepping for
> > > dev_base_lock will see the current usage and not make a lot out of it.
> > >
> > > I'm not really sure how to order this rework to be honest.
> >
> > We can not have a mix of RCU /rwlock/mutex. It must be one, because of
> > bonding/teaming.
> >
> > So all existing uses of rwlock / RCU need to be removed.
> >
> > This is probably not trivial.
>
> Now, "it's going to look nasty" is one thing, whereas "it won't work" is
> completely different. I think it would work though, so could you expand
> on why you're saying we can't have the mix?
You can not use dev_base_lock() or RCU and call an ndo_get_stats64()
that could sleep.
You can not for example start changing bonding, since bond_get_stats()
could be called from non-sleepable context (net/core/net-procfs.c)
I am still referring to your patch adding :
+ if (!rtnl_locked)
+ rtnl_lock();
This is all I said.
next prev parent reply other threads:[~2020-11-30 21:46 UTC|newest]
Thread overview: 28+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <20201129182435.jgqfjbekqmmtaief@skbuf>
2020-11-29 20:58 ` Correct usage of dev_base_lock in 2020 Vladimir Oltean
2020-11-30 5:12 ` Stephen Hemminger
2020-11-30 10:41 ` Eric Dumazet
2020-11-30 18:14 ` Jakub Kicinski
2020-11-30 18:30 ` Eric Dumazet
2020-11-30 18:48 ` Vladimir Oltean
2020-11-30 19:00 ` Eric Dumazet
2020-11-30 19:03 ` Vladimir Oltean
2020-11-30 19:22 ` Eric Dumazet
2020-11-30 19:32 ` Vladimir Oltean
2020-11-30 21:41 ` Florian Fainelli
2020-11-30 19:46 ` Vladimir Oltean
2020-11-30 20:18 ` Eric Dumazet
2020-11-30 20:21 ` Stephen Hemminger
2020-11-30 20:26 ` Vladimir Oltean
2020-11-30 20:29 ` Eric Dumazet
2020-11-30 20:36 ` Vladimir Oltean
2020-11-30 20:43 ` Eric Dumazet
2020-11-30 20:50 ` Vladimir Oltean
2020-11-30 21:00 ` Eric Dumazet
2020-11-30 21:11 ` Vladimir Oltean
2020-11-30 21:46 ` Eric Dumazet [this message]
2020-11-30 21:53 ` Vladimir Oltean
2020-11-30 22:20 ` Eric Dumazet
2020-11-30 22:41 ` Vladimir Oltean
2020-12-01 14:42 ` Pablo Neira Ayuso
2020-12-01 18:58 ` Vladimir Oltean
2020-12-10 4:32 ` [PATCH] net: bonding: retrieve device statistics under RTNL, not RCU kernel test robot
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