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	<20101214212904.17022.16604.stgit@mike.mtv.corp.google.com>
Date: Wed, 15 Dec 2010 00:15:23 +0100
Message-ID: <AANLkTi=reqRMrv4k5EZKdj7pmsomApw9=Kwh9nxfKCuJ@mail.gmail.com>
Subject: Re: [PATCH v3 02/22] netconsole: Introduce locking over the netpoll fields
From: =?ISO-8859-2?Q?Micha=B3_Miros=B3aw?= <mirqus@gmail.com>
To: Mike Waychison <mikew@google.com>
Cc: simon.kagstrom@netinsight.net, davem@davemloft.net, nhorman@tuxdriver.com,
        Matt Mackall <mpm@selenic.com>, adurbin@google.com,
        linux-kernel@vger.kernel.org, chavey@google.com,
        Greg KH <greg@kroah.com>, netdev@vger.kernel.org,
        =?ISO-8859-1?Q?Am=E9rico_Wang?= <xiyou.wangcong@gmail.com>,
        akpm@linux-foundation.org, linux-api@vger.kernel.org
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2010/12/14 Mike Waychison <mikew@google.com>:
> The netconsole driver currently doesn't do any locking over its
> configuration fields. ?This can cause problems if we were to ever have
> concurrent writing to fields while somebody is enabling the service.
>
> For simplicity, this patch extends targets_list_lock to cover all
> configuration fields within the targets. ?Macros are also added here to
> wrap accessors so that we check whether the target has been enabled with
> locking handled.
>
> Signed-off-by: Mike Waychison <mikew@google.com>
> Acked-by: Matt Mackall <mpm@selenic.com>
> ---
> ?drivers/net/netconsole.c | ?114 ++++++++++++++++++++++++++--------------------
> ?1 files changed, 64 insertions(+), 50 deletions(-)
>
> diff --git a/drivers/net/netconsole.c b/drivers/net/netconsole.c
> index c87a49e..6e16888 100644
> --- a/drivers/net/netconsole.c
> +++ b/drivers/net/netconsole.c
> @@ -327,6 +327,7 @@ static ssize_t store_enabled(struct netconsole_target *nt,
> ? ? ? ? ? ? ? ? ? ? ? ? ? ? const char *buf,
> ? ? ? ? ? ? ? ? ? ? ? ? ? ? size_t count)
> ?{
> + ? ? ? unsigned long flags;
> ? ? ? ?int err;
> ? ? ? ?long enabled;
>
> @@ -335,6 +336,10 @@ static ssize_t store_enabled(struct netconsole_target *nt,
> ? ? ? ? ? ? ? ?return enabled;
>
> ? ? ? ?if (enabled) { ?/* 1 */
> + ? ? ? ? ? ? ? spin_lock_irqsave(&target_list_lock, flags);
> + ? ? ? ? ? ? ? if (nt->enabled)
> + ? ? ? ? ? ? ? ? ? ? ? goto busy;
> + ? ? ? ? ? ? ? spin_unlock_irqrestore(&target_list_lock, flags);
>

This looks wrong. Unless there is another lock or mutex covering this
function, at this point (after spin_unlock_irqrestore()) another
thread might set nt->enabled = 1.

Best Regards,
Micha? Miros?aw
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