netdev - Re: [PATCH] drop_monitor: prevent init path from scheduling on the wrong cpu

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Message-Id: <20120502.210258.1086419954037969029.davem@davemloft.net>
Date:	Wed, 02 May 2012 21:02:58 -0400 (EDT)
From:	David Miller <davem@...emloft.net>
To:	nhorman@...driver.com
Cc:	netdev@...r.kernel.org
Subject: Re: [PATCH] drop_monitor: prevent init path from scheduling on the
 wrong cpu

From: Neil Horman <nhorman@...driver.com>
Date: Tue,  1 May 2012 14:18:02 -0400

> I just noticed after some recent updates, that the init path for the drop
> monitor protocol has a minor error.  drop monitor maintains a per cpu structure,
> that gets initalized from a single cpu.  Normally this is fine, as the protocol
> isn't in use yet, but I recently made a change that causes a failed skb
> allocation to reschedule itself .  Given the current code, the implication is
> that this workqueue reschedule will take place on the wrong cpu.  If drop
> monitor is used early during the boot process, its possible that two cpus will
> access a single per-cpu structure in parallel, possibly leading to data
> corruption.
> 
> This patch fixes the situation, by storing the cpu number that a given instance
> of this per-cpu data should be accessed from.  In the case of a need for a
> reschedule, the cpu stored in the struct is assigned the rescheule, rather than
> the currently executing cpu
> 
> Tested successfully by myself.
> 
> Signed-off-by: Neil Horman <nhorman@...driver.com>

Applied, thanks Neil.
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