linux-kernel - Re: [PATCH v2 3/3] pppoatm: protect against freeing of vcc

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Message-ID: <1354141115.21562.101.camel@shinybook.infradead.org>
Date:	Wed, 28 Nov 2012 22:18:35 +0000
From:	David Woodhouse <dwmw2@...radead.org>
To:	David Laight <David.Laight@...LAB.COM>
Cc:	chas williams - CONTRACTOR <chas@....nrl.navy.mil>,
	Krzysztof Mazur <krzysiek@...lesie.net>, davem@...emloft.net,
	netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
	nathan@...verse.com.au
Subject: Re: [PATCH v2 3/3] pppoatm: protect against freeing of vcc

On Wed, 2012-11-28 at 09:21 +0000, David Laight wrote:
> Even when it might make sense to sleep in close until tx drains
> there needs to be a finite timeout before it become abortive.

You are, of course, right. We should never wait for hardware for ever.
And just to serve me right, I seem to have hit a bug in the latest Solos
firmware (1.11) which makes it sometimes lock up when I reboot. So it
never responds to the PKT_PCLOSE packet... and thus it deadlocks when I
try to kill pppd and unload the module to reset it :)

New version...

From 53dd01c08fec5b26006a009b25e4210127fdb27a Mon Sep 17 00:00:00 2001
From: David Woodhouse <David.Woodhouse@...el.com>
Date: Tue, 27 Nov 2012 23:49:24 +0000
Subject: [PATCH] solos-pci: Wait for pending TX to complete when releasing
 vcc

We should no longer be calling the old pop routine for the vcc, after
vcc_release() has completed. Make sure we wait for any pending TX skbs
to complete, by waiting for our own PKT_PCLOSE control skb to be sent.

Signed-off-by: David Woodhouse <David.Woodhouse@...el.com>
---
 drivers/atm/solos-pci.c | 17 +++++++++++++++--
 1 file changed, 15 insertions(+), 2 deletions(-)

diff --git a/drivers/atm/solos-pci.c b/drivers/atm/solos-pci.c
index 9851093..3720670 100644
--- a/drivers/atm/solos-pci.c
+++ b/drivers/atm/solos-pci.c
@@ -92,6 +92,7 @@ struct pkt_hdr {
 };
 
 struct solos_skb_cb {
+	struct completion c;
 	struct atm_vcc *vcc;
 	uint32_t dma_addr;
 };
@@ -881,11 +882,18 @@ static void pclose(struct atm_vcc *vcc)
 	header->vci = cpu_to_le16(vcc->vci);
 	header->type = cpu_to_le16(PKT_PCLOSE);
 
+	init_completion(&SKB_CB(skb)->c);
+
 	fpga_queue(card, SOLOS_CHAN(vcc->dev), skb, NULL);
 
 	clear_bit(ATM_VF_ADDR, &vcc->flags);
 	clear_bit(ATM_VF_READY, &vcc->flags);
 
+	if (!wait_for_completion_timeout(&SKB_CB(skb)->c,
+					 jiffies + msecs_to_jiffies(5000)))
+		dev_warn(&card->dev->dev, "Timeout waiting for VCC close on port %d\n",
+			 SOLOS_CHAN(vcc->dev));
+
 	/* Hold up vcc_destroy_socket() (our caller) until solos_bh() in the
 	   tasklet has finished processing any incoming packets (and, more to
 	   the point, using the vcc pointer). */
@@ -1011,9 +1019,12 @@ static uint32_t fpga_tx(struct solos_card *card)
 			if (vcc) {
 				atomic_inc(&vcc->stats->tx);
 				solos_pop(vcc, oldskb);
-			} else
+			} else {
+				struct pkt_hdr *header = (void *)oldskb->data;
+				if (le16_to_cpu(header->type) == PKT_PCLOSE)
+					complete(&SKB_CB(oldskb)->c);
 				dev_kfree_skb_irq(oldskb);
-
+			}
 		}
 	}
 	/* For non-DMA TX, write the 'TX start' bit for all four ports simultaneously */
@@ -1345,6 +1356,8 @@ static struct pci_driver fpga_driver = {
 
 static int __init solos_pci_init(void)
 {
+	BUILD_BUG_ON(sizeof(struct solos_skb_cb) > sizeof(((struct sk_buff *)0)->cb));
+
 	printk(KERN_INFO "Solos PCI Driver Version %s\n", VERSION);
 	return pci_register_driver(&fpga_driver);
 }
-- 
1.8.0


-- 
dwmw2


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