netdev - Re: [Bonding-devel] [PATCH] bonding: fix WARN_ON when writing to bond

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Date:	Mon, 4 Oct 2010 22:26:17 -0400
From:	Neil Horman <nhorman@...driver.com>
To:	Stephen Hemminger <shemminger@...tta.com>
Cc:	netdev@...r.kernel.org, fubar@...ibm.com,
	bonding-devel@...ts.sourceforge.net, davem@...emloft.net
Subject: Re: [Bonding-devel] [PATCH] bonding: fix WARN_ON when writing to
 bond_master sysfs file

On Tue, Oct 05, 2010 at 09:57:13AM +0900, Stephen Hemminger wrote:
> On Mon, 4 Oct 2010 16:21:12 -0400
> Neil Horman <nhorman@...driver.com> wrote:
> 
> > Fix a WARN_ON failure in bond_masters sysfs file
> > 
> > Got a report of this warning recently
> > 
> > bonding: bond0 is being created...
> > ------------[ cut here ]------------
> > WARNING: at fs/proc/generic.c:590 proc_register+0x14d/0x185()
> > Hardware name: ProLiant BL465c G1
> > proc_dir_entry 'bonding/bond0' already registered
> > Modules linked in: bonding ipv6 tg3 bnx2 shpchp amd64_edac_mod edac_core
> > ipmi_si
> > ipmi_msghandler serio_raw i2c_piix4 k8temp edac_mce_amd hpwdt microcode hpsa
> > cc
> > iss radeon ttm drm_kms_helper drm i2c_algo_bit i2c_core [last unloaded:
> > scsi_wai
> > t_scan]
> > Pid: 935, comm: ifup-eth Not tainted 2.6.33.5-124.fc13.x86_64 #1
> > Call Trace:
> > [<ffffffff8104b54c>] warn_slowpath_common+0x77/0x8f
> > [<ffffffff8104b5b1>] warn_slowpath_fmt+0x3c/0x3e
> > [<ffffffff8114bf0b>] proc_register+0x14d/0x185
> > [<ffffffff8114c20c>] proc_create_data+0x87/0xa1
> > [<ffffffffa0211e9b>] bond_create_proc_entry+0x55/0x95 [bonding]
> > [<ffffffffa0215e5d>] bond_init+0x95/0xd0 [bonding]
> > [<ffffffff8138cd97>] register_netdevice+0xdd/0x29e
> > [<ffffffffa021240b>] bond_create+0x8e/0xb8 [bonding]
> > [<ffffffffa021c4be>] bonding_store_bonds+0xb3/0x1c1 [bonding]
> > [<ffffffff812aec85>] class_attr_store+0x27/0x29
> > [<ffffffff8115423d>] sysfs_write_file+0x10f/0x14b
> > [<ffffffff81101acf>] vfs_write+0xa9/0x106
> > [<ffffffff81101be2>] sys_write+0x45/0x69
> > [<ffffffff81009b02>] system_call_fastpath+0x16/0x1b
> > ---[ end trace a677c3f7f8b16b1e ]---
> > bonding: Bond creation failed.
> > 
> > It happens because a user space writer to bond_master can try to register and
> > already existing bond interface name.  Fix it by teaching bond_create to check
> > for the existance of devices with that name first in cases where a non-NULL name
> > parameter has been passed in
> > 
> > Signed-off-by: Neil Horman <nhorman@...driver.com>
> > 
> > bond_main.c |   16 +++++++++++++++-
> > 1 file changed, 15 insertions(+), 1 deletion(-)
> > 
> > diff --git a/drivers/net/bonding/bond_main.c b/drivers/net/bonding/bond_main.c
> > index fb70c3e..10e4ffe 100644
> > --- a/drivers/net/bonding/bond_main.c
> > +++ b/drivers/net/bonding/bond_main.c
> > @@ -5148,7 +5148,7 @@ static struct rtnl_link_ops bond_link_ops __read_mostly = {
> >   */
> >  int bond_create(struct net *net, const char *name)
> >  {
> > -	struct net_device *bond_dev;
> > +	struct net_device *bond_dev, *check_dev;
> >  	int res;
> >  
> >  	rtnl_lock();
> > @@ -5168,6 +5168,20 @@ int bond_create(struct net *net, const char *name)
> >  		res = dev_alloc_name(bond_dev, "bond%d");
> >  		if (res < 0)
> >  			goto out;
> > +	} else {
> > +		/*
> > +		 * If we're given a name to register
> > +		 * we need to ensure that its not already
> > +		 * registered
> > +		 */
> > +		check_dev = dev_get_by_name(net, name);
> > +
> > +		res = (check_dev) ? 0 : -EEXIST;
> > +
> > +		dev_put(check_dev);
> > +
> > +		if (res)
> > +			goto out;
> >  	}
> >  
> >  	res = register_netdevice(bond_dev);
> 
> Why is this necessary?
> register_netdevice does already check for duplicate name so please
> use it's return value instead
> 
No, its the call to register_netdev that causes the WARN_ON.  Check the stack
trace, register_netdev call bond_init which in turn registers a proc interface
by an existing name, which causes the WARN_ON

> If that doesn't work then use __dev_get_by_name to avoid
> ref count (ie dev_put).
> 
Yeah, thats a good idea.  I'll respin this in the AM.  Thanks!

Regards
Neil

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