linux-kernel - Re: [PATCH 4.4 026/124] iwlwifi: pcie: fix race in Rx buffer allocator

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Message-ID: <1536172759.3024.44.camel@codethink.co.uk>
Date:   Wed, 05 Sep 2018 19:39:19 +0100
From:   Ben Hutchings <ben.hutchings@...ethink.co.uk>
To:     Shaul Triebitz <shaul.triebitz@...el.com>,
        Luca Coelho <luciano.coelho@...el.com>
Cc:     stable@...r.kernel.org,
        Sasha Levin <alexander.levin@...rosoft.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 4.4 026/124] iwlwifi: pcie: fix race in Rx buffer
 allocator

On Sat, 2018-08-04 at 11:00 +0200, Greg Kroah-Hartman wrote:
> 4.4-stable review patch.  If anyone has any objections, please let me know.
> 
> ------------------
> 
> From: Shaul Triebitz <shaul.triebitz@...el.com>
> 
> [ Upstream commit 0f22e40053bd5378ad1e3250e65c574fd61c0cd6 ]
> 
> Make sure the rx_allocator worker is canceled before running the
> rx_init routine.  rx_init frees and re-allocates all rxb's pages.  The
> rx_allocator worker also allocates pages for the used rxb's.  Running
> rx_init and rx_allocator simultaniously causes a kernel panic.  Fix
> that by canceling the work in rx_init.
> 
> Signed-off-by: Shaul Triebitz <shaul.triebitz@...el.com>
> Signed-off-by: Luca Coelho <luciano.coelho@...el.com>
> Signed-off-by: Sasha Levin <alexander.levin@...rosoft.com>
> Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
> ---
>  drivers/net/wireless/iwlwifi/pcie/rx.c |    2 ++
>  1 file changed, 2 insertions(+)
> 
> --- a/drivers/net/wireless/iwlwifi/pcie/rx.c
> +++ b/drivers/net/wireless/iwlwifi/pcie/rx.c
> @@ -713,6 +713,8 @@ int iwl_pcie_rx_init(struct iwl_trans *t
>  						WQ_HIGHPRI | WQ_UNBOUND, 1);
>  	INIT_WORK(&rba->rx_alloc, iwl_pcie_rx_allocator_work);
>  
> +	cancel_work_sync(&rba->rx_alloc);
> +
>  	spin_lock(&rba->lock);
>  	atomic_set(&rba->req_pending, 0);
>  	atomic_set(&rba->req_ready, 0);

This seems to be an incomplete fix.  INIT_WORK() will overwrite the
list pointers in the work item, so there is still a race condition.

I think that the RX initialisation and reinitialisation/reset cases
need to be explicitly distinguished.  In the initialisation case the
driver should do only INIT_WORK() and in the reset case it should do
only cancel_work_sync() (although it would be safe to do INIT_WORK()
*after* that).

Ben.

-- 
Ben Hutchings, Software Developer                         Codethink Ltd
https://www.codethink.co.uk/                 Dale House, 35 Dale Street
                                     Manchester, M1 2HF, United Kingdom