netdev - Re: netdev: question on ndo_set_rx

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Date:	Mon, 21 Sep 2015 13:15:26 -0400
From:	Murali Karicheri <m-karicheri2@...com>
To:	open list: TI NETCP ETHERNET DRIVER <netdev@...r.kernel.org>,
	David Miller <davem@...emloft.net>, ;
Subject: Re: netdev: question on ndo_set_rx_mode() API

On 09/18/2015 01:07 PM, Murali Karicheri wrote:
> Hello Netdev experts,
>
> I am seeing an issue with netcp driver that has a mutex lock/unlock()
> call. When kernel hack debug options are enabled, I see a warning that
> this function is taking a mutex that can sleep and is not allowed. I am
> working to fix this. Looking at other drivers, I see many drivers such
> as e1000_main.c are not holding any driver specific lock as part of the
> API implementation. So my first attempt is to remove the mutex. But
> wondering what kind of synchronization is required in this API to run it
> properly on an SMP kernel. Based on my search following files are
> calling dev_change_flags() which in turn calls ndo_set_rx_mode()
>
> Set-1
> ======
> net/ipv4/devinet.c
> net/ipv4/ipconfig.c
> net/core/dev_ioctl.c
>
> Set-2
> =====
> net/8021q/vlan.c
> net/core/rtnetlink.c
>
> Set-1 seems to call this with rtnl_lock (mutex) held. So there is
> already protection between processes that calls this function and driver
> doesn't need to provide any explicit synchronization. Is this correct?
>
> For Set-2, I can't figure out in what context this is calling this API
> Can someone help me understand this?
>
> However I see below.
>
> Documentation/networking/netdevices.txt explains,
>
> ndo_set_rx_mode:
> Synchronization: netif_addr_lock spinlock.
> Context: BHs disabled
>
> So is there any synchronization required from the driver perspective? If
> yes, what kind of synchronization is needed? Thanks in advance for your
> response.
>
Any help??

Thanks.

-- 
Murali Karicheri
Linux Kernel, Keystone
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