As &hc->lock is acquired by both timer _hfcpci_softirq() and hardirq
hfcpci_int(), the timer should disable irq before lock acquisition
otherwise deadlock could happen if the timmer is preemtped by the hadr irq.

Possible deadlock scenario:
hfcpci_softirq() (timer)
    -> _hfcpci_softirq()
    -> spin_lock(&hc->lock);
        <irq interruption>
        -> hfcpci_int()
        -> spin_lock(&hc->lock); (deadlock here)

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

The tentative patch fixes the potential deadlock by spin_lock_irq()
in timer.

Fixes: b36b654a7e82 ("mISDN: Create /sys/class/mISDN")
Signed-off-by: Chengfeng Ye <dg573847474@gmail.com>

Changes in v2
- change dev_kfree_skb() to dev_kfree_skb_any() inside spin_lock_irq()
  critical region
---
 drivers/isdn/hardware/mISDN/hfcpci.c | 10 +++++-----
 1 file changed, 5 insertions(+), 5 deletions(-)

diff --git a/drivers/isdn/hardware/mISDN/hfcpci.c b/drivers/isdn/hardware/mISDN/hfcpci.c
index c0331b268010..fe391de1aba3 100644
--- a/drivers/isdn/hardware/mISDN/hfcpci.c
+++ b/drivers/isdn/hardware/mISDN/hfcpci.c
@@ -839,7 +839,7 @@ hfcpci_fill_fifo(struct bchannel *bch)
 		*z1t = cpu_to_le16(new_z1);	/* now send data */
 		if (bch->tx_idx < bch->tx_skb->len)
 			return;
-		dev_kfree_skb(bch->tx_skb);
+		dev_kfree_skb_any(bch->tx_skb);
 		if (get_next_bframe(bch))
 			goto next_t_frame;
 		return;
@@ -895,7 +895,7 @@ hfcpci_fill_fifo(struct bchannel *bch)
 	}
 	bz->za[new_f1].z1 = cpu_to_le16(new_z1);	/* for next buffer */
 	bz->f1 = new_f1;	/* next frame */
-	dev_kfree_skb(bch->tx_skb);
+	dev_kfree_skb_any(bch->tx_skb);
 	get_next_bframe(bch);
 }
 
@@ -1119,7 +1119,7 @@ tx_birq(struct bchannel *bch)
 	if (bch->tx_skb && bch->tx_idx < bch->tx_skb->len)
 		hfcpci_fill_fifo(bch);
 	else {
-		dev_kfree_skb(bch->tx_skb);
+		dev_kfree_skb_any(bch->tx_skb);
 		if (get_next_bframe(bch))
 			hfcpci_fill_fifo(bch);
 	}
@@ -2277,7 +2277,7 @@ _hfcpci_softirq(struct device *dev, void *unused)
 		return 0;
 
 	if (hc->hw.int_m2 & HFCPCI_IRQ_ENABLE) {
-		spin_lock(&hc->lock);
+		spin_lock_irq(&hc->lock);
 		bch = Sel_BCS(hc, hc->hw.bswapped ? 2 : 1);
 		if (bch && bch->state == ISDN_P_B_RAW) { /* B1 rx&tx */
 			main_rec_hfcpci(bch);
@@ -2288,7 +2288,7 @@ _hfcpci_softirq(struct device *dev, void *unused)
 			main_rec_hfcpci(bch);
 			tx_birq(bch);
 		}
-		spin_unlock(&hc->lock);
+		spin_unlock_irq(&hc->lock);
 	}
 	return 0;
 }
-- 
2.17.1

Hello:

This patch was applied to netdev/net.git (main)
by Jakub Kicinski <kuba@kernel.org>:

On Thu, 27 Jul 2023 08:56:19 +0000 you wrote:
> As &hc->lock is acquired by both timer _hfcpci_softirq() and hardirq
> hfcpci_int(), the timer should disable irq before lock acquisition
> otherwise deadlock could happen if the timmer is preemtped by the hadr irq.
> 
> Possible deadlock scenario:
> hfcpci_softirq() (timer)
>     -> _hfcpci_softirq()
>     -> spin_lock(&hc->lock);
>         <irq interruption>
>         -> hfcpci_int()
>         -> spin_lock(&hc->lock); (deadlock here)
> 
> [...]

Here is the summary with links:
  - [v2] mISDN: hfcpci: Fix potential deadlock on &hc->lock
    https://git.kernel.org/netdev/net/c/56c6be35fcbe

You are awesome, thank you!
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