netdev - Re: [PATCH] Fix deadlock between boomerang_interrupt and boomerang_start

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Date:	Mon, 23 Aug 2010 22:01:34 +0200
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Neil Horman <nhorman@...driver.com>
Cc:	netdev@...r.kernel.org
Subject: Re: [PATCH] Fix deadlock between boomerang_interrupt and
 boomerang_start_tx in 3c59x

Le mercredi 11 août 2010 à 11:12 -0400, Neil Horman a écrit :
> If netconsole is in use, there is a possibility for deadlock in 3c59x between
> boomerang_interrupt and boomerang_start_xmit.  Both routines take the vp->lock,
> and if netconsole is in use, a pr_* call from the boomerang_interrupt routine
> will result in the netconsole code attempting to trnasmit an skb, which can try
> to take the same spin lock, resulting in deadlock.
> 
> The fix is pretty straightforward.  This patch allocats a bit in the 3c59x
> private structure to indicate that its handling an interrupt.  If we get into
> the transmit routine and that bit is set, we can be sure that we have recursed
> and will deadlock if we continue, so instead we just return NETDEV_TX_BUSY, so
> the stack requeues the skb to try again later.
> 
> Signed-off-by: Neil Horman <nhorman@...driver.com>
> ---
>  drivers/net/3c59x.c |   15 ++++++++++++++-
>  1 files changed, 14 insertions(+), 1 deletions(-)
> 
> diff --git a/drivers/net/3c59x.c b/drivers/net/3c59x.c
> index c754d88..c685a55 100644
> --- a/drivers/net/3c59x.c
> +++ b/drivers/net/3c59x.c
> @@ -633,7 +633,8 @@ struct vortex_private {
>  		open:1,
>  		medialock:1,
>  		must_free_region:1,				/* Flag: if zero, Cardbus owns the I/O region */
> -		large_frames:1;			/* accept large frames */
> +		large_frames:1,			/* accept large frames */
> +		handling_irq:1;			/* private in_irq indicator */


It would be safer and faster to use a dedicated 'int' instead of a
bitfield.



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