linux-kernel - RE: [PATCH] bonding: avoid repeated display of same link status change

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Message-ID: <78bf3185-fbd1-4a6c-ae32-70da0af2cbb4@default>
Date:   Mon, 17 Sep 2018 22:05:44 -0700 (PDT)
From:   Manish Kumar Singh <mk.singh@...cle.com>
To:     Eric Dumazet <eric.dumazet@...il.com>, netdev@...r.kernel.org
Cc:     Jay Vosburgh <j.vosburgh@...il.com>,
        Veaceslav Falico <vfalico@...il.com>,
        Andy Gospodarek <andy@...yhouse.net>,
        "David S. Miller" <davem@...emloft.net>,
        linux-kernel@...r.kernel.org
Subject: RE: [PATCH] bonding: avoid repeated display of same link status
 change



> -----Original Message-----
> From: Eric Dumazet [mailto:eric.dumazet@...il.com]
> Sent: 17 सितम्बर 2018 20:08
> To: Manish Kumar Singh; netdev@...r.kernel.org
> Cc: Jay Vosburgh; Veaceslav Falico; Andy Gospodarek; David S. Miller; linux-
> kernel@...r.kernel.org
> Subject: Re: [PATCH] bonding: avoid repeated display of same link status
> change
> 
> 
> 
> On 09/17/2018 12:20 AM, mk.singh@...cle.com wrote:
> > From: Manish Kumar Singh <mk.singh@...cle.com>
> >
> > When link status change needs to be committed and rtnl lock couldn't be
> > taken, avoid redisplay of same link status change message.
> >
> > Signed-off-by: Manish Kumar Singh <mk.singh@...cle.com>
> > ---
> >  drivers/net/bonding/bond_main.c | 6 ++++--
> >  include/net/bonding.h           | 1 +
> >  2 files changed, 5 insertions(+), 2 deletions(-)
> >
> > diff --git a/drivers/net/bonding/bond_main.c
> b/drivers/net/bonding/bond_main.c
> > index 217b790d22ed..fb4e3aff1677 100644
> > --- a/drivers/net/bonding/bond_main.c
> > +++ b/drivers/net/bonding/bond_main.c
> > @@ -2087,7 +2087,7 @@ static int bond_miimon_inspect(struct bonding
> *bond)
> >  			bond_propose_link_state(slave, BOND_LINK_FAIL);
> >  			commit++;
> >  			slave->delay = bond->params.downdelay;
> > -			if (slave->delay) {
> > +			if (slave->delay && !bond->rtnl_needed) {
> >  				netdev_info(bond->dev, "link status down for
> %sinterface %s, disabling it in %d ms\n",
> >  					    (BOND_MODE(bond) ==
> >  					     BOND_MODE_ACTIVEBACKUP) ?
> > @@ -2127,7 +2127,7 @@ static int bond_miimon_inspect(struct bonding
> *bond)
> >  			commit++;
> >  			slave->delay = bond->params.updelay;
> >
> > -			if (slave->delay) {
> > +			if (slave->delay && !bond->rtnl_needed) {
> >  				netdev_info(bond->dev, "link status up for
> interface %s, enabling it in %d ms\n",
> >  					    slave->dev->name,
> >  					    ignore_updelay ? 0 :
> > @@ -2301,9 +2301,11 @@ static void bond_mii_monitor(struct
> work_struct *work)
> >  		if (!rtnl_trylock()) {
> >  			delay = 1;
> >  			should_notify_peers = false;
> > +			bond->rtnl_needed = true;
> 
> How can you set a shared variable with no synchronization ?
Thanks Eric for reviewing the patch. rtnl_needed is not a shared variable, it is part of bonding structure, that is one per bonding driver instance. There can't be two parallel instances of bond_miimon_inspect for a single  bonding driver instance at any given point of time. and only bond_miimon_inspect updates it. That’s why I think there is no need of any synchronization here.  

> 
> A bool is particularly dangerous here, at least on some arches.
Thank you for cautioning us on bool usage. even a u8 can meet our requirement.  we will change it.  but; if time permits can you share more on "particularly dangerous here, at least on some arches".

F
> 
> >  			goto re_arm;
> >  		}
> >
> > +		bond->rtnl_needed = false;
> >  		bond_for_each_slave(bond, slave, iter) {
> >  			bond_commit_link_state(slave,
> BOND_SLAVE_NOTIFY_LATER);
> >  		}
> > diff --git a/include/net/bonding.h b/include/net/bonding.h
> > index 808f1d167349..50d61cf77855 100644
> > --- a/include/net/bonding.h
> > +++ b/include/net/bonding.h
> > @@ -234,6 +234,7 @@ struct bonding {
> >  	struct	 dentry *debug_dir;
> >  #endif /* CONFIG_DEBUG_FS */
> >  	struct rtnl_link_stats64 bond_stats;
> > +	bool rtnl_needed;
> >  };
> >
> >  #define bond_slave_get_rcu(dev) \
> >