cxgb3: Fix lockdep problems with sge.reg_lock

cxgb3: Fix lockdep problems with sge.reg_lock

[Roland Dreier]

Using iWARP with a Chelsio T3 NIC generates the following lockdep warning:

    =================================
    [ INFO: inconsistent lock state ]
    2.6.25-rc6 #50
    ---------------------------------
    inconsistent {softirq-on-W} -> {in-softirq-W} usage.
    swapper/0 [HC0[0]:SC1[1]:HE0:SE0] takes:
     (&adap->sge.reg_lock){-+..}, at: [<ffffffff880e5ee2>] cxgb_offload_ctl+0x3af/0x507 [cxgb3]

The problem is that reg_lock is used with plain spin_lock() in
drivers/net/cxgb3/sge.c but is used with spin_lock_irqsave() in
drivers/net/cxgb3/cxgb3_offload.c.  This is technically a false
positive, since the uses in sge.c are only in the initialization and
cleanup paths and cannot overlap with any use in interrupt context.

The best fix is probably just to use spin_lock_irq() with reg_lock in
sge.c.  Even though it's not strictly required for correctness, it
avoids triggering lockdep and the extra overhead of disabling
interrupts is not important at all in the initialization and cleanup
slow paths.

Signed-off-by: Roland Dreier <rolandd@cisco.com>
---
diff --git a/drivers/net/cxgb3/sge.c b/drivers/net/cxgb3/sge.c
index 979f3fc..d82f864 100644
--- a/drivers/net/cxgb3/sge.c
+++ b/drivers/net/cxgb3/sge.c
@@ -557,9 +557,9 @@ static void t3_free_qset(struct adapter *adapter, struct sge_qset *q)
 
 	for (i = 0; i < SGE_RXQ_PER_SET; ++i)
 		if (q->fl[i].desc) {
-			spin_lock(&adapter->sge.reg_lock);
+			spin_lock_irq(&adapter->sge.reg_lock);
 			t3_sge_disable_fl(adapter, q->fl[i].cntxt_id);
-			spin_unlock(&adapter->sge.reg_lock);
+			spin_unlock_irq(&adapter->sge.reg_lock);
 			free_rx_bufs(pdev, &q->fl[i]);
 			kfree(q->fl[i].sdesc);
 			dma_free_coherent(&pdev->dev,
@@ -570,9 +570,9 @@ static void t3_free_qset(struct adapter *adapter, struct sge_qset *q)
 
 	for (i = 0; i < SGE_TXQ_PER_SET; ++i)
 		if (q->txq[i].desc) {
-			spin_lock(&adapter->sge.reg_lock);
+			spin_lock_irq(&adapter->sge.reg_lock);
 			t3_sge_enable_ecntxt(adapter, q->txq[i].cntxt_id, 0);
-			spin_unlock(&adapter->sge.reg_lock);
+			spin_unlock_irq(&adapter->sge.reg_lock);
 			if (q->txq[i].sdesc) {
 				free_tx_desc(adapter, &q->txq[i],
 					     q->txq[i].in_use);
@@ -586,9 +586,9 @@ static void t3_free_qset(struct adapter *adapter, struct sge_qset *q)
 		}
 
 	if (q->rspq.desc) {
-		spin_lock(&adapter->sge.reg_lock);
+		spin_lock_irq(&adapter->sge.reg_lock);
 		t3_sge_disable_rspcntxt(adapter, q->rspq.cntxt_id);
-		spin_unlock(&adapter->sge.reg_lock);
+		spin_unlock_irq(&adapter->sge.reg_lock);
 		dma_free_coherent(&pdev->dev,
 				  q->rspq.size * sizeof(struct rsp_desc),
 				  q->rspq.desc, q->rspq.phys_addr);
@@ -2661,7 +2661,7 @@ int t3_sge_alloc_qset(struct adapter *adapter, unsigned int id, int nports,
 		(16 * 1024) - SKB_DATA_ALIGN(sizeof(struct skb_shared_info)) :
 		MAX_FRAME_SIZE + 2 + sizeof(struct cpl_rx_pkt);
 
-	spin_lock(&adapter->sge.reg_lock);
+	spin_lock_irq(&adapter->sge.reg_lock);
 
 	/* FL threshold comparison uses < */
 	ret = t3_sge_init_rspcntxt(adapter, q->rspq.cntxt_id, irq_vec_idx,
@@ -2705,7 +2705,7 @@ int t3_sge_alloc_qset(struct adapter *adapter, unsigned int id, int nports,
 			goto err_unlock;
 	}
 
-	spin_unlock(&adapter->sge.reg_lock);
+	spin_unlock_irq(&adapter->sge.reg_lock);
 
 	q->adap = adapter;
 	q->netdev = dev;
@@ -2722,7 +2722,7 @@ int t3_sge_alloc_qset(struct adapter *adapter, unsigned int id, int nports,
 	return 0;
 
       err_unlock:
-	spin_unlock(&adapter->sge.reg_lock);
+	spin_unlock_irq(&adapter->sge.reg_lock);
       err:
 	t3_free_qset(adapter, q);
 	return ret;

Re: cxgb3: Fix lockdep problems with sge.reg_lock

[Divy Le Ray]

Roland Dreier wrote:
> Using iWARP with a Chelsio T3 NIC generates the following lockdep warning:
>
>     =================================
>     [ INFO: inconsistent lock state ]
>     2.6.25-rc6 #50
>     ---------------------------------
>     inconsistent {softirq-on-W} -> {in-softirq-W} usage.
>     swapper/0 [HC0[0]:SC1[1]:HE0:SE0] takes:
>      (&adap->sge.reg_lock){-+..}, at: [<ffffffff880e5ee2>] cxgb_offload_ctl+0x3af/0x507 [cxgb3]
>
> The problem is that reg_lock is used with plain spin_lock() in
> drivers/net/cxgb3/sge.c but is used with spin_lock_irqsave() in
> drivers/net/cxgb3/cxgb3_offload.c.  This is technically a false
> positive, since the uses in sge.c are only in the initialization and
> cleanup paths and cannot overlap with any use in interrupt context.
>
> The best fix is probably just to use spin_lock_irq() with reg_lock in
> sge.c.  Even though it's not strictly required for correctness, it
> avoids triggering lockdep and the extra overhead of disabling
> interrupts is not important at all in the initialization and cleanup
> slow paths.
>
> Signed-off-by: Roland Dreier <rolandd@cisco.com>
>   
Acked-by: Divy Le Ray <divy@chelsio.com>

As you mention, the current code is correct even if lockdep disagrees.


Cheers,
Divy

Re: cxgb3: Fix lockdep problems with sge.reg_lock

[Jeff Garzik]

Roland Dreier wrote:
> Using iWARP with a Chelsio T3 NIC generates the following lockdep warning:
> 
>     =================================
>     [ INFO: inconsistent lock state ]
>     2.6.25-rc6 #50
>     ---------------------------------
>     inconsistent {softirq-on-W} -> {in-softirq-W} usage.
>     swapper/0 [HC0[0]:SC1[1]:HE0:SE0] takes:
>      (&adap->sge.reg_lock){-+..}, at: [<ffffffff880e5ee2>] cxgb_offload_ctl+0x3af/0x507 [cxgb3]
> 
> The problem is that reg_lock is used with plain spin_lock() in
> drivers/net/cxgb3/sge.c but is used with spin_lock_irqsave() in
> drivers/net/cxgb3/cxgb3_offload.c.  This is technically a false
> positive, since the uses in sge.c are only in the initialization and
> cleanup paths and cannot overlap with any use in interrupt context.
> 
> The best fix is probably just to use spin_lock_irq() with reg_lock in
> sge.c.  Even though it's not strictly required for correctness, it
> avoids triggering lockdep and the extra overhead of disabling
> interrupts is not important at all in the initialization and cleanup
> slow paths.
> 
> Signed-off-by: Roland Dreier <rolandd@cisco.com>

applied