netdev - [PATCH] stmmac: Clear variable when destroying workqueue

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Date: Wed, 21 Feb 2024 15:32:33 +0100
From: Jakub Raczynski <j.raczynski@...sung.com>
To: netdev@...r.kernel.org
Cc: alexandre.torgue@...s.st.com, joabreu@...opsys.com, Jakub Raczynski
	<j.raczynski@...sung.com>
Subject: [PATCH] stmmac: Clear variable when destroying workqueue

Currently when suspending driver and stopping workqueue it is checked whether
workqueue is not NULL and if so, it is destroyed.
Function destroy_workqueue() does drain queue and does clear variable, but
it does not set workqueue variable to NULL. This can cause kernel/module
panic if code attempts to clear workqueue that was not initialized.

This scenario is possible when resuming suspended driver in stmmac_resume(),
because there is no handling for failed stmmac_hw_setup(),
which can fail and return if DMA engine has failed to initialize,
and workqueue is initialized after DMA engine.
Should DMA engine fail to initialize, resume will proceed normally,
but interface won't work and TX queue will eventually timeout,
causing 'Reset adapter' error.
This then does destroy workqueue during reset process.
And since workqueue is initialized after DMA engine and can be skipped,
it will cause kernel/module panic.

This commit sets workqueue variable to NULL when destroying workqueue,
which secures against that possible driver crash.

Signed-off-by: Jakub Raczynski <j.raczynski@...sung.com>
---
 drivers/net/ethernet/stmicro/stmmac/stmmac_main.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c b/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
index 75d029704503..0681029a2489 100644
--- a/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
+++ b/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
@@ -4005,8 +4005,10 @@ static void stmmac_fpe_stop_wq(struct stmmac_priv *priv)
 {
 	set_bit(__FPE_REMOVING, &priv->fpe_task_state);

-	if (priv->fpe_wq)
+	if (priv->fpe_wq) {
 		destroy_workqueue(priv->fpe_wq);
+		priv->fpe_wq = NULL;
+	}

 	netdev_info(priv->dev, "FPE workqueue stop");
 }
-- 
2.34.1