netdev - Re: [PATCH net] mlx4_core: fix race on comm channel

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Date:	Sun, 18 Mar 2012 05:55:51 -0700
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Yevgeny Petrilin <yevgenyp@...lanox.co.il>
Cc:	davem@...emloft.net, netdev@...r.kernel.org, eugenia@...lanox.co.il
Subject: Re: [PATCH net] mlx4_core: fix race on comm channel

Le dimanche 18 mars 2012 à 14:18 +0200, Yevgeny Petrilin a écrit :
> From: Eugenia Emantayev <eugenia@...lanox.co.il>
> 
> Prevent race condition between commands on comm channel.
> Happened while unloading the driver when switching from
> event to polling mode. VF got completion on the last command
> before switching to polling mode, but toggle was not changed.
> After the fix - VF will not write the next command before
> toggle is updated.
> 
> Signed-off-by: Eugenia Emantayev <eugenia@...lanox.co.il>
> ---
>  drivers/net/ethernet/mellanox/mlx4/cmd.c |    8 ++++++++
>  1 files changed, 8 insertions(+), 0 deletions(-)
> 
> diff --git a/drivers/net/ethernet/mellanox/mlx4/cmd.c b/drivers/net/ethernet/mellanox/mlx4/cmd.c
> index eaf09d4..2f1f4a1 100644
> --- a/drivers/net/ethernet/mellanox/mlx4/cmd.c
> +++ b/drivers/net/ethernet/mellanox/mlx4/cmd.c
> @@ -239,6 +239,7 @@ static int mlx4_comm_cmd_wait(struct mlx4_dev *dev, u8 op,
>  {
>  	struct mlx4_cmd *cmd = &mlx4_priv(dev)->cmd;
>  	struct mlx4_cmd_context *context;
> +	unsigned long end;
>  	int err = 0;
>  
>  	down(&cmd->event_sem);
> @@ -268,6 +269,13 @@ static int mlx4_comm_cmd_wait(struct mlx4_dev *dev, u8 op,
>  	}
>  
>  out:
> +	/* wait for comm channel ready
> +	   this is necessary for prevention the race
> +	   when switching between event to polling mode */
> +	end = msecs_to_jiffies(timeout) + jiffies;
> +	while (comm_pending(dev) && time_before(jiffies, end))
> +		cond_resched();
> +
>  	spin_lock(&cmd->context_lock);
>  	context->next = cmd->free_head;
>  	cmd->free_head = context - cmd->context;

David wants your comment like this :

	/* dfgdgg rertert cxvcvcxv 
	 * sddsf sdfsdfdsf sfddfd dfdfd fdfdfdfd df
	 * bxvqir sdjqpo cqljcdlskjs d.
	 */

(I wont comment on the grammar)


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