netdev - [PATCH] ks8851: Fix deadlock with the SPI chip variant

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Message-ID: <20240703160053.9892-1-rwahl@gmx.de>
Date: Wed,  3 Jul 2024 18:00:53 +0200
From: Ronald Wahl <rwahl@....de>
To: Ronald Wahl <rwahl@....de>
Cc: Ronald Wahl <ronald.wahl@...itan.com>,
	"David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>,
	Jakub Kicinski <kuba@...nel.org>,
	Paolo Abeni <pabeni@...hat.com>,
	Simon Horman <horms@...nel.org>,
	netdev@...r.kernel.org,
	stable@...r.kernel.org
Subject: [PATCH] ks8851: Fix deadlock with the SPI chip variant

From: Ronald Wahl <ronald.wahl@...itan.com>

When SMP is enabled and spinlocks are actually functional then there is
a deadlock with the 'statelock' spinlock between ks8851_start_xmit_spi
and ks8851_irq:

    watchdog: BUG: soft lockup - CPU#0 stuck for 27s!
    call trace:
      queued_spin_lock_slowpath+0x100/0x284
      do_raw_spin_lock+0x34/0x44
      ks8851_start_xmit_spi+0x30/0xb8
      ks8851_start_xmit+0x14/0x20
      netdev_start_xmit+0x40/0x6c
      dev_hard_start_xmit+0x6c/0xbc
      sch_direct_xmit+0xa4/0x22c
      __qdisc_run+0x138/0x3fc
      qdisc_run+0x24/0x3c
      net_tx_action+0xf8/0x130
      handle_softirqs+0x1ac/0x1f0
      __do_softirq+0x14/0x20
      ____do_softirq+0x10/0x1c
      call_on_irq_stack+0x3c/0x58
      do_softirq_own_stack+0x1c/0x28
      __irq_exit_rcu+0x54/0x9c
      irq_exit_rcu+0x10/0x1c
      el1_interrupt+0x38/0x50
      el1h_64_irq_handler+0x18/0x24
      el1h_64_irq+0x64/0x68
      __netif_schedule+0x6c/0x80
      netif_tx_wake_queue+0x38/0x48
      ks8851_irq+0xb8/0x2c8
      irq_thread_fn+0x2c/0x74
      irq_thread+0x10c/0x1b0
      kthread+0xc8/0xd8
      ret_from_fork+0x10/0x20

This issue has not been identified earlier because tests were done on
a device with SMP disabled and so spinlocks were actually NOPs.

This commit moves the netif_wake_queue call outside the spinlock
protected area.

Fixes: 3dc5d4454545 ("net: ks8851: Fix TX stall caused by TX buffer overrun")
Cc: "David S. Miller" <davem@...emloft.net>
Cc: Eric Dumazet <edumazet@...gle.com>
Cc: Jakub Kicinski <kuba@...nel.org>
Cc: Paolo Abeni <pabeni@...hat.com>
Cc: Simon Horman <horms@...nel.org>
Cc: netdev@...r.kernel.org
Cc: stable@...r.kernel.org # 5.10+
Signed-off-by: Ronald Wahl <ronald.wahl@...itan.com>
---
 drivers/net/ethernet/micrel/ks8851_common.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/drivers/net/ethernet/micrel/ks8851_common.c b/drivers/net/ethernet/micrel/ks8851_common.c
index 6453c92f0fa7..60b959126b26 100644
--- a/drivers/net/ethernet/micrel/ks8851_common.c
+++ b/drivers/net/ethernet/micrel/ks8851_common.c
@@ -348,15 +348,17 @@ static irqreturn_t ks8851_irq(int irq, void *_ks)

 	if (status & IRQ_TXI) {
 		unsigned short tx_space = ks8851_rdreg16(ks, KS_TXMIR);
+		bool need_wake_queue;

 		netif_dbg(ks, intr, ks->netdev,
 			  "%s: txspace %d\n", __func__, tx_space);

 		spin_lock(&ks->statelock);
 		ks->tx_space = tx_space;
-		if (netif_queue_stopped(ks->netdev))
-			netif_wake_queue(ks->netdev);
+		need_wake_queue = netif_queue_stopped(ks->netdev);
 		spin_unlock(&ks->statelock);
+		if (need_wake_queue)
+			netif_wake_queue(ks->netdev);
 	}

 	if (status & IRQ_SPIBEI) {
--
2.45.2