netdev - Re: [net-2.6 PATCH 5/6] net: fix sock locking for sk

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Message-Id: <20090917.182745.230999703.davem@davemloft.net>
Date:	Thu, 17 Sep 2009 18:27:45 -0700 (PDT)
From:	David Miller <davem@...emloft.net>
To:	jeffrey.t.kirsher@...el.com
Cc:	netdev@...r.kernel.org, gospo@...hat.com,
	linux-scsi@...r.kernel.org, john.r.fastabend@...el.com
Subject: Re: [net-2.6 PATCH 5/6] net: fix sock locking for sk_err field in
 netlink.

From: Jeff Kirsher <jeffrey.t.kirsher@...el.com>
Date: Thu, 17 Sep 2009 17:58:32 -0700

> From: John Fastabend <john.r.fastabend@...el.com>
> 
> This adds the sock lock around setting the sk_err field
> in sock struct. Without the lock multiple threads may
> write to this field.
> 
> Signed-off-by: John Fastabend <john.r.fastabend@...el.com>
> Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@...el.com>

This isn't right.

Writes to sk->sk_err can occur asynchronously just fine and
without any locking.

The only requirement is that consumers of the sk_err value
use sock_error() which uses xchg() to get and clear the
value atomically.
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