From: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
To: Cong Wang <xiyou.wangcong@gmail.com>
Cc: Rolf Neugebauer <rolf.neugebauer@docker.com>,
LKML <linux-kernel@vger.kernel.org>,
Linux Kernel Network Developers <netdev@vger.kernel.org>,
Justin Cormack <justin.cormack@docker.com>,
Ian Campbell <ian.campbell@docker.com>
Subject: Re: Long delays creating a netns after deleting one (possibly RCU related)
Date: Mon, 14 Nov 2016 08:24:17 -0800 [thread overview]
Message-ID: <20161114162417.GJ4127@linux.vnet.ibm.com> (raw)
In-Reply-To: <CAM_iQpUq14GsvGyz2xA1PkDq5YO743T68Zh2zm=NJZQ9S2Ahqg@mail.gmail.com>
On Sun, Nov 13, 2016 at 10:47:01PM -0800, Cong Wang wrote:
> On Fri, Nov 11, 2016 at 4:55 PM, Cong Wang <xiyou.wangcong@gmail.com> wrote:
> > On Fri, Nov 11, 2016 at 4:23 PM, Paul E. McKenney
> > <paulmck@linux.vnet.ibm.com> wrote:
> >>
> >> Ah! This net_mutex is different than RTNL. Should synchronize_net() be
> >> modified to check for net_mutex being held in addition to the current
> >> checks for RTNL being held?
> >>
> >
> > Good point!
> >
> > Like commit be3fc413da9eb17cce0991f214ab0, checking
> > for net_mutex for this case seems to be an optimization, I assume
> > synchronize_rcu_expedited() and synchronize_rcu() have the same
> > behavior...
>
> Thinking a bit more, I think commit be3fc413da9eb17cce0991f
> gets wrong on rtnl_is_locked(), the lock could be locked by other
> process not by the current one, therefore it should be
> lockdep_rtnl_is_held() which, however, is defined only when LOCKDEP
> is enabled... Sigh.
>
> I don't see any better way than letting callers decide if they want the
> expedited version or not, but this requires changes of all callers of
> synchronize_net(). Hm.
I must confess that I don't understand how it would help to use an
expedited grace period when some other process is holding RTNL.
In contrast, I do well understand how it helps when the current process
is holding RTNL.
So what am I missing here?
Thanx, Paul
next prev parent reply other threads:[~2016-11-14 16:24 UTC|newest]
Thread overview: 17+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-11-09 15:42 Long delays creating a netns after deleting one (possibly RCU related) Rolf Neugebauer
2016-11-10 17:37 ` Cong Wang
2016-11-10 21:24 ` Paul E. McKenney
2016-11-11 13:11 ` Rolf Neugebauer
2016-11-12 0:23 ` Paul E. McKenney
2016-11-12 0:55 ` Cong Wang
2016-11-14 6:47 ` Cong Wang
2016-11-14 16:24 ` Paul E. McKenney [this message]
2016-11-14 17:44 ` Cong Wang
2016-11-14 18:14 ` Paul E. McKenney
2016-11-14 22:12 ` Eric W. Biederman
2016-11-14 22:46 ` Eric Dumazet
2016-11-14 23:09 ` Eric Dumazet
2016-11-18 0:31 ` Jarno Rajahalme
2016-11-19 0:38 ` Jarno Rajahalme
2016-11-19 0:41 ` Eric Dumazet
2016-11-14 17:29 ` Hannes Frederic Sowa
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