On 25-03-18 11:09:32, Ralph Siemsen wrote:

The cdns3 driver has the same NCM deadlock as fixed in cdnsp by commit 58f2fcb3a845 ("usb: cdnsp: Fix deadlock issue during using NCM gadget").

Under PREEMPT_RT the deadlock can be readily triggered by heavy network traffic, for example using "iperf --bidir" over NCM ethernet link.

The deadlock occurs because the threaded interrupt handler gets preempted by a softirq, but both are protected by the same spinlock. Prevent deadlock by disabling softirq during threaded irq handler.

cc: stable@vger.kernel.org Fixes: 7733f6c32e36 ("usb: cdns3: Add Cadence USB3 DRD Driver") Signed-off-by: Ralph Siemsen ralph.siemsen@linaro.org

Acked-by: Peter Chen peter.chen@kernel.org

---

v2 changes:

• move the fix up the call stack, as per discussion at

https://lore.kernel.org/linux-rt-devel/20250226082931.-XRIDa6D@linutronix.de...

drivers/usb/cdns3/cdns3-gadget.c | 2 ++ 1 file changed, 2 insertions(+)

diff --git a/drivers/usb/cdns3/cdns3-gadget.c b/drivers/usb/cdns3/cdns3-gadget.c index fd1beb10bba72..19101ff1cf1bd 100644 --- a/drivers/usb/cdns3/cdns3-gadget.c +++ b/drivers/usb/cdns3/cdns3-gadget.c @@ -1963,6 +1963,7 @@ static irqreturn_t cdns3_device_thread_irq_handler(int irq, void *data) unsigned int bit; unsigned long reg;

• local_bh_disable(); spin_lock_irqsave(&priv_dev->lock, flags);

reg = readl(&priv_dev->regs->usb_ists); @@ -2004,6 +2005,7 @@ static irqreturn_t cdns3_device_thread_irq_handler(int irq, void *data) irqend: writel(~0, &priv_dev->regs->ep_ien); spin_unlock_irqrestore(&priv_dev->lock, flags);

• local_bh_enable();

return ret; }

---

base-commit: 4701f33a10702d5fc577c32434eb62adde0a1ae1 change-id: 20250312-rfs-cdns3-deadlock-697df5cad3ce

Best regards,

Ralph Siemsen ralph.siemsen@linaro.org