Re: [added to the 4.1 stable tree] switchdev: Require RTNL mutex to be held when sending FDB notifications

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From: Ido Schimmel <idosch@xxxxxxxxxxxx>
Date: Thu, 3 Mar 2016 11:35:31 +0200

> Hi Sasha,
> 
> Wed, Mar 02, 2016 at 10:23:52PM IST, sasha.levin@xxxxxxxxxx wrote:
>>From: Ido Schimmel <idosch@xxxxxxxxxxxx>
>>
>>This patch has been added to the 4.1 stable tree. If you have any
>>objections, please let us know.
>>
>>===============
>>
>>[ Upstream commit 4f2c6ae5c64c353fb1b0425e4747e5603feadba1 ]
>>
>>When switchdev drivers process FDB notifications from the underlying
>>device they resolve the netdev to which the entry points to and notify
>>the bridge using the switchdev notifier.
>>
>>However, since the RTNL mutex is not held there is nothing preventing
>>the netdev from disappearing in the middle, which will cause
>>br_switchdev_event() to dereference a non-existing netdev.
>>
>>Make switchdev drivers hold the lock at the beginning of the
>>notification processing session and release it once it ends, after
>>notifying the bridge.
>>
>>Also, remove switchdev_mutex and fdb_lock, as they are no longer needed
>>when RTNL mutex is held.
> 
> You removed the fdb_lock bits from the commit below since they aren't
> present in kernel 4.1. Can you remove it from the description as well?
> Should probably be:
> 
> "Also, remove switchdev_mutex, as it's no longer needed when RTNL mutex
> is held."

No, I did this, and I do not think editing the commit log message
contents are appropriate for stable backports ever!

You can add notes in a "[]" bracketed section, but that's it.
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