RE: [PATCH RFC] bonding: rate-limit bonding driver inspect messages

[Praveen Kannoju]

> -----Original Message-----
> From: Hangbin Liu <liuhangbin@xxxxxxxxx>
> Sent: 16 February 2024 02:33 PM
> To: Praveen Kannoju <praveen.kannoju@xxxxxxxxxx>
> Cc: j.vosburgh@xxxxxxxxx; andy@xxxxxxxxxxxxx; davem@xxxxxxxxxxxxx; edumazet@xxxxxxxxxx; kuba@xxxxxxxxxx;
> pabeni@xxxxxxxxxx; netdev@xxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx; Rajesh Sivaramasubramaniom
> <rajesh.sivaramasubramaniom@xxxxxxxxxx>; Rama Nichanamatlu <rama.nichanamatlu@xxxxxxxxxx>; Manjunath Patil
> <manjunath.b.patil@xxxxxxxxxx>
> Subject: Re: [PATCH RFC] bonding: rate-limit bonding driver inspect messages
> 
> On Thu, Feb 15, 2024 at 10:55:54PM +0530, Praveen Kumar Kannoju wrote:
> > Rate limit bond driver log messages, to prevent a log flood in a
> > run-away situation, e.g couldn't get rtnl lock. Message flood leads to
> > instability of system and loss of other crucial messages.
> 
> Hi Praveen,
> 
> The patch looks good to me. But would you please help explain why these
> slave_info() are chosen under net_ratelimit?
> 
> Thanks
> Hangbin

Thank you, Hangbin.

The routine bond_mii_monitor() periodically inspects the slave carrier state in order to detect for state changes, on a state change internally records it and does the state change action.

Parked-to-Parked state changes goes through transient state. As an example for Up to Down, BOND_LINK_UP to BOND_LINK_DOWN, is thru BOND_LINK_FAIL.  In order to attain next parked state or transient state bond needs rtnl mutex If in a situation it cannot get it, a state change wouldn't happen.  In order to achieve a state change as quickly as possible  bond_mii_monitor() reschedules itself to come around after 1 msec. And every single come around reinspects the link and sees a state change compared to its internally recorded, which in reality internal state could be not changed earlier as failed to get rtnl lock, and throws again log indicating it sees a state change If attaining rtnl mutex take long say hypothetical 5 secs, then bond logs 5000 state change message. 1 message at every 1 msec. 

And in production environments we have seen bond taking long to achieve a state as someone else holding rtnl. Many processes do get rtnl lock.  As an example we can see eth drivers. They hold rtnl mutex for the entire duration while performing a fault recovery. There are many such scenarios.

This patch doesn't change -how- bond functions. It only simply limits this kind of log flood. 

-
Praveen.
> >
> > v2: Use exising net_ratelimit() instead of introducing new rate-limit
> > parameter.
> >
> > Signed-off-by: Praveen Kumar Kannoju <praveen.kannoju@xxxxxxxxxx>
> > ---
> >  drivers/net/bonding/bond_main.c | 36
> > ++++++++++++++++++++----------------
> >  1 file changed, 20 insertions(+), 16 deletions(-)
> >
> > diff --git a/drivers/net/bonding/bond_main.c
> > b/drivers/net/bonding/bond_main.c index 4e0600c..e92eba1 100644
> > --- a/drivers/net/bonding/bond_main.c
> > +++ b/drivers/net/bonding/bond_main.c
> > @@ -2610,12 +2610,13 @@ static int bond_miimon_inspect(struct bonding *bond)
> >  			commit++;
> >  			slave->delay = bond->params.downdelay;
> >  			if (slave->delay) {
> > -				slave_info(bond->dev, slave->dev, "link status down for %sinterface, disabling it in %d ms\n",
> > -					   (BOND_MODE(bond) ==
> > -					    BOND_MODE_ACTIVEBACKUP) ?
> > -					    (bond_is_active_slave(slave) ?
> > -					     "active " : "backup ") : "",
> > -					   bond->params.downdelay * bond->params.miimon);
> > +				if (net_ratelimit())
> > +					slave_info(bond->dev, slave->dev, "link status down for %sinterface, disabling it in %d ms\n",
> > +						   (BOND_MODE(bond) ==
> > +						   BOND_MODE_ACTIVEBACKUP) ?
> > +						   (bond_is_active_slave(slave) ?
> > +						   "active " : "backup ") : "",
> > +						   bond->params.downdelay * bond->params.miimon);
> >  			}
> >  			fallthrough;
> >  		case BOND_LINK_FAIL:
> > @@ -2623,9 +2624,10 @@ static int bond_miimon_inspect(struct bonding *bond)
> >  				/* recovered before downdelay expired */
> >  				bond_propose_link_state(slave, BOND_LINK_UP);
> >  				slave->last_link_up = jiffies;
> > -				slave_info(bond->dev, slave->dev, "link status up again after %d ms\n",
> > -					   (bond->params.downdelay - slave->delay) *
> > -					   bond->params.miimon);
> > +				if (net_ratelimit())
> > +					slave_info(bond->dev, slave->dev, "link status up again after %d ms\n",
> > +						   (bond->params.downdelay - slave->delay) *
> > +						   bond->params.miimon);
> >  				commit++;
> >  				continue;
> >  			}
> > @@ -2648,18 +2650,20 @@ static int bond_miimon_inspect(struct bonding *bond)
> >  			slave->delay = bond->params.updelay;
> >
> >  			if (slave->delay) {
> > -				slave_info(bond->dev, slave->dev, "link status up, enabling it in %d ms\n",
> > -					   ignore_updelay ? 0 :
> > -					   bond->params.updelay *
> > -					   bond->params.miimon);
> > +				if (net_ratelimit())
> > +					slave_info(bond->dev, slave->dev, "link status up, enabling it in %d ms\n",
> > +						   ignore_updelay ? 0 :
> > +						   bond->params.updelay *
> > +						   bond->params.miimon);
> >  			}
> >  			fallthrough;
> >  		case BOND_LINK_BACK:
> >  			if (!link_state) {
> >  				bond_propose_link_state(slave, BOND_LINK_DOWN);
> > -				slave_info(bond->dev, slave->dev, "link status down again after %d ms\n",
> > -					   (bond->params.updelay - slave->delay) *
> > -					   bond->params.miimon);
> > +				if (net_ratelimit())
> > +					slave_info(bond->dev, slave->dev, "link status down again after %d ms\n",
> > +						   (bond->params.updelay - slave->delay) *
> > +						   bond->params.miimon);
> >  				commit++;
> >  				continue;
> >  			}
> > --
> > 1.8.3.1
> >