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From:   Chengfeng Ye <dg573847474@gmail.com>
To:     3chas3@gmail.com, davem@davemloft.net, horms@kernel.org
Cc:     linux-atm-general@lists.sourceforge.net, netdev@vger.kernel.org,
        linux-kernel@vger.kernel.org, Chengfeng Ye <dg573847474@gmail.com>
Subject: [PATCH v2 2/2] atm: solos-pci: Fix potential deadlock on &tx_queue_lock
Date:   Thu,  5 Oct 2023 07:49:17 +0000
Message-Id: <20231005074917.65161-1-dg573847474@gmail.com>
Precedence: bulk

As &card->tx_queue_lock is 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 #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 &card->tx_queue_lock under process context code consistently to
prevent the possible deadlock scenario.

Fixes: 213e85d38912 ("solos-pci: clean up pclose() function")
Signed-off-by: Chengfeng Ye <dg573847474@gmail.com>
---
V2: add fix tag, and split into two patches

 drivers/atm/solos-pci.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/drivers/atm/solos-pci.c b/drivers/atm/solos-pci.c
index 48cf9b36b61a..247e9200e312 100644
--- a/drivers/atm/solos-pci.c
+++ b/drivers/atm/solos-pci.c
@@ -955,16 +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