From: Subash Abhinov Kasiviswanathan <subashab@codeaurora•org>
To: David Miller <davem@davemloft•net>
Cc: netdev@vger•kernel.org, fengguang.wu@intel•com, dcbw@redhat•com,
jiri@resnulli•us, stephen@networkplumber•org,
David.Laight@aculab•com, marcel@holtmann•org, andrew@lunn•ch
Subject: Re: [PATCH net-next 3/3 v9] drivers: net: ethernet: qualcomm: rmnet: Initial implementation
Date: Mon, 28 Aug 2017 11:40:39 -0600 [thread overview]
Message-ID: <86de09154bfe0b4e13ac5fcc9090389a@codeaurora.org> (raw)
In-Reply-To: <20170825.200623.1467784779129980276.davem@davemloft.net>
>
> In these code paths where you are the writer, you have to rely upon
> the RTNL mutex (or some other mutual exclusion mechanism) to protect
> the update operation. RCU locking itself does not provide this.
>
> So you should use something like rcu_dereference_rtnl() or similar.
>
> So this would be rmnet_force_unassociate_device() and rmnet_dellink()
>
> RCU is subtle and the writer paths have the be handled differently
> from the reader paths. Please take some time to study how RCU should
> be applied properly in these situations rather than just slapping a
> patch together overnight.
>
> Thank you.
Sorry about the mess David.
Can you tell me if the following design is correct -
The shared resource which needs to be protected is
real_dev->rx_handler_data.
For the writer path, this needs to be protected using rtnl_lock() and
rcu.
The writer paths are rmnet_newlink(), rmnet_delink() and
rmnet_force_unassociate_device(). These paths are already called with
rtnl_lock() acquired in, so we just need to acquire the rcu_read_lock().
To
dereference here, we will need to use rtnl_dereference().
For the reader path, the real_dev->rx_handler_data is called in the TX /
RX
path. We only need rcu_read_lock() for these scenarios. In these cases,
the rcu_read_lock() is held in __dev_queue_xmit() and
netif_receive_skb_internal(), so readers need to use
rcu_dereference_rtnl()
to get the relevant information.
prev parent reply other threads:[~2017-08-28 17:40 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-08-25 4:39 [PATCH net-next 0/3 v9] Add support for rmnet driver Subash Abhinov Kasiviswanathan
2017-08-25 4:39 ` [PATCH net-next 1/3 v9] net: ether: Add support for multiplexing and aggregation type Subash Abhinov Kasiviswanathan
2017-08-28 22:22 ` Dan Williams
2017-08-29 3:00 ` Subash Abhinov Kasiviswanathan
2017-08-25 4:39 ` [PATCH net-next 2/3 v9] net: arp: Add support for raw IP device Subash Abhinov Kasiviswanathan
2017-08-25 4:39 ` [PATCH net-next 3/3 v9] drivers: net: ethernet: qualcomm: rmnet: Initial implementation Subash Abhinov Kasiviswanathan
2017-08-26 3:06 ` David Miller
2017-08-28 17:40 ` Subash Abhinov Kasiviswanathan [this message]
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