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From:   Chengfeng Ye <dg573847474@gmail.com>
To:     3chas3@gmail.com, davem@davemloft.net
Cc:     linux-atm-general@lists.sourceforge.net, netdev@vger.kernel.org,
        linux-kernel@vger.kernel.org, Chengfeng Ye <dg573847474@gmail.com>
Subject: [PATCH] atm: solos-pci: Fix potential deadlock on &cli_queue_lock and &tx_queue_lock
Date:   Tue, 26 Sep 2023 10:44:42 +0000
Message-Id: <20230926104442.8684-1-dg573847474@gmail.com>
Precedence: bulk

As &card->cli_queue_lock and &card->tx_queue_lock are acquired under
softirq context along the following call chain from solos_bh(), other
acquisition of the same lock inside process context should disable
at least bh to avoid double lock.

<deadlock #1>
console_show()
--> spin_lock(&card->cli_queue_lock)
<interrupt>
   --> solos_bh()
   --> spin_lock(&card->cli_queue_lock)

<deadlock #2>
pclose()
--> spin_lock(&card->tx_queue_lock)
<interrupt>
   --> solos_bh()
   --> fpga_tx()
   --> spin_lock(&card->tx_queue_lock)

This flaw was found by an experimental static analysis tool I am
developing for irq-related deadlock.

To prevent the potential deadlock, the patch uses spin_lock_irqsave()
on the two locks under process context code consistently to prevent
the possible deadlock scenario.

Signed-off-by: Chengfeng Ye <dg573847474@gmail.com>
---
 drivers/atm/solos-pci.c | 10 ++++++----
 1 file changed, 6 insertions(+), 4 deletions(-)

diff --git a/drivers/atm/solos-pci.c b/drivers/atm/solos-pci.c
index 94fbc3abe60e..247e9200e312 100644
--- a/drivers/atm/solos-pci.c
+++ b/drivers/atm/solos-pci.c
@@ -447,11 +447,12 @@ static ssize_t console_show(struct device *dev, struct device_attribute *attr,
 	struct atm_dev *atmdev = container_of(dev, struct atm_dev, class_dev);
 	struct solos_card *card = atmdev->dev_data;
 	struct sk_buff *skb;
+	unsigned long flags;
 	unsigned int len;
 
-	spin_lock(&card->cli_queue_lock);
+	spin_lock_irqsave(&card->cli_queue_lock, flags);
 	skb = skb_dequeue(&card->cli_queue[SOLOS_CHAN(atmdev)]);
-	spin_unlock(&card->cli_queue_lock);
+	spin_unlock_irqrestore(&card->cli_queue_lock, flags);
 	if(skb == NULL)
 		return sprintf(buf, "No data.\n");
 
@@ -954,16 +955,17 @@ static void pclose(struct atm_vcc *vcc)
 	unsigned char port = SOLOS_CHAN(vcc->dev);
 	struct sk_buff *skb, *tmpskb;
 	struct pkt_hdr *header;
+	unsigned long flags;
 
 	/* Remove any yet-to-be-transmitted packets from the pending queue */
-	spin_lock(&card->tx_queue_lock);
+	spin_lock_irqsave(&card->tx_queue_lock, flags);
 	skb_queue_walk_safe(&card->tx_queue[port], skb, tmpskb) {
 		if (SKB_CB(skb)->vcc == vcc) {
 			skb_unlink(skb, &card->tx_queue[port]);
 			solos_pop(vcc, skb);
 		}
 	}
-	spin_unlock(&card->tx_queue_lock);
+	spin_unlock_irqrestore(&card->tx_queue_lock, flags);
 
 	skb = alloc_skb(sizeof(*header), GFP_KERNEL);
 	if (!skb) {
-- 
2.17.1