Subject: Re: [PATCH / RFC 2/2] fec: fixup spinlocks.

From: Greg Ungerer <[email-masked]>
Date: Fri, 28 Mar 2008 16:58:09 +1000

Hi Sebastion,

Sebastian Siewior wrote:
> 1. Initialize the spinlock
> 2. Fix the following spinlock recursion:
> 
> |BUG: spinlock recursion on CPU#0, swapper/1
> | lock: 00253484, .magic: dead4ead, .owner: swapper/1, .owner_cpu: 0
> |Stack from 00219d04:
> |        0002951e 00144b04 000afaca 00253484 001753a2 00002704 000c5ef6 00253484
> |        00800000 0025302d 002533e0 0002951e 00253000 0004857a 00144baa 00253484
> |        00000000 000c5550 00253484 00172acd 000c5ef6 0017689c 0014aca3 00253484
> |        00020013 00252000 002533e0 40001000 000c602e 00253000 600e0000 000c5ef6
> |        001a6d68 40001000 000c57c0 00020013 00253000 00172acd 000c5faa 00176a11
> |        0014ac96 000c5faa 00000000 00000000 0000005d 00000033 00219eaa 00000001
> |Possible Call Trace:
> | printk+0x0/0x20
> | _spin_unlock+0x0/0x6
> | _raw_spin_lock+0xfc/0x160
> | mii_discover_phy3+0x0/0xb4
> | printk+0x0/0x20
> | note_interrupt+0x0/0x28a
> | _spin_lock_irqsave+0x16/0x1e
> | mii_queue+0x4c/0x124
> | mii_discover_phy3+0x0/0xb4
> | _start+0x13/0x7c
> | mii_discover_phy+0x84/0x90
> | mii_discover_phy3+0x0/0xb4
> | fec_enet_interrupt+0x158/0x472
> 
> We call from inet context (fec_enet_interrupt, holding the spinlock) the
> first callback (which is mii_discover_phy(), initialized in fec_enet_init()).
> mii_discover_phy() calls mii_queue() which takes the spinlock again, boom.
> The fix is to drop the spinlock in interrupt context after the list
> modification.
> 
> 3. Use spin_unlock_irq / spin_lock_irq in the IRQ functions (IRQ is not
> registered with the IRQ off flag) and  dev->hard_start_xmit callback.
> 4. Use the .*_irqsave variant in that part which may be called from IRQ or
> user mode.

I couldn't see any changes here that switched to use *_irqsave?

Regards
Greg

> Signed-off-by: Sebastian Siewior <[email-masked]>
> --- a/drivers/net/fec.c
> +++ b/drivers/net/fec.c
> @@ -117,9 +117,11 @@ static unsigned char	fec_mac_default[] =
>  /* Forward declarations of some structures to support different PHYs
>  */
>  
> +typedef void (mii_func)(uint val, struct net_device *dev);
> +
>  typedef struct {
>  	uint mii_data;
> -	void (*funct)(uint mii_reg, struct net_device *dev);
> +	mii_func *funct;
>  } phy_cmd_t;
>  
>  typedef struct {
> @@ -261,7 +263,7 @@ static mii_list_t	*mii_head;
>  static mii_list_t	*mii_tail;
>  
>  static int	mii_queue(struct net_device *dev, int request,
> -				void (*func)(uint, struct net_device *));
> +				mii_func *func);
>  
>  /* Make MII read/write commands for the FEC.
>  */
> @@ -503,7 +505,7 @@ fec_enet_tx(struct net_device *dev)
>  	struct	sk_buff	*skb;
>  
>  	fep = netdev_priv(dev);
> -	spin_lock(&fep->lock);
> +	spin_lock_irq(&fep->lock);
>  	bdp = fep->dirty_tx;
>  
>  	while (((status = bdp->cbd_sc) & BD_ENET_TX_READY) == 0) {
> @@ -562,7 +564,7 @@ fec_enet_tx(struct net_device *dev)
>  		}
>  	}
>  	fep->dirty_tx = (cbd_t *)bdp;
> -	spin_unlock(&fep->lock);
> +	spin_unlock_irq(&fep->lock);
>  }
>  
>  
> @@ -705,12 +707,13 @@ fec_enet_mii(struct net_device *dev)
>  	volatile fec_t	*ep;
>  	mii_list_t	*mip;
>  	uint		mii_reg;
> +	mii_func *mii_func = NULL;
>  
>  	fep = netdev_priv(dev);
>  	ep = fep->hwp;
>  	mii_reg = ep->fec_mii_data;
>  
> -	spin_lock(&fep->lock);
> +	spin_lock_irq(&fep->lock);
>  
>  	if ((mip = mii_head) == NULL) {
>  		printk("MII and no head!\n");
> @@ -718,7 +721,7 @@ fec_enet_mii(struct net_device *dev)
>  	}
>  
>  	if (mip->mii_func != NULL)
> -		(*(mip->mii_func))(mii_reg, dev);
> +		mii_func = *(mip->mii_func);
>  
>  	mii_head = mip->mii_next;
>  	mip->mii_next = mii_free;
> @@ -728,11 +731,13 @@ fec_enet_mii(struct net_device *dev)
>  		ep->fec_mii_data = mip->mii_regval;
>  
>  unlock:
> -	spin_unlock(&fep->lock);
> +	spin_unlock_irq(&fep->lock);
> +	if (mii_func)
> +		mii_func(mii_reg, dev);
>  }
>  
>  static int
> -mii_queue(struct net_device *dev, int regval, void (*func)(uint, struct net_device *))
> +mii_queue(struct net_device *dev, int regval, mii_func *func)
>  {
>  	struct fec_enet_private *fep;
>  	unsigned long	flags;
> @@ -2343,6 +2348,7 @@ int __init fec_enet_init(struct net_devi
>  	*/
>  	fecp = (volatile fec_t *) fec_hw[index];
>  
> +	spin_lock_init(&fep->lock);
>  	fep->index = index;
>  	fep->hwp = fecp;
>  	fep->netdev = dev;
> 

-- 
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Greg Ungerer  --  Chief Software Dude       EMAIL:     [email-masked]
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