On Thu, 2024-09-26 at 21:39 +0200, Hubert Wiśniewski wrote: > I'm a bit at loss here. The deadlock seems to be unrelated to netif_rx() > (which is not being called in the interrupt context after all), yet > replacing it with __netif_rx() fixes the lockup (though a warning is still > generated, which suggests that the patch does not completely fix the > issue). Well, never mind. After some investigation, I think the problem is as follows: 1. musb_g_giveback() releases the musb lock using spin_unlock(). The lock is now released, but hardirqs are still disabled. 2. Then, usb_gadget_giveback_request() is called, which in turn calls rx_complete(). This does not happen in the interrupt context, so netif_rx() disables bottom havles, then enables them using local_bh_enable(). 3. This leads to calling __local_bh_enable_ip(), which gives off a warning (the first backtrace) that hardirqs are disabled. Then, hardirqs are disabled (again?), and then enabled (as they should have been in the first place). 4. After usb_gadget_giveback_request() returns, musb_g_giveback() acquires the musb lock using spin_lock(). This does not disable hardirqs, so they are still enabled. 5. While the musb lock is acquired, an interrupt occurs. It is handled by dsps_interrupt(), which acquires the musb lock. A deadlock occurs. Replacing netif_rx() with __netif_rx() apparently fixes this part, as it does not lead to any change of hardirq state. There is still one problem though: rx_complete() is usually called from the interrupt context, except when the network interface is brought up. I think one solution would be to make musb_g_giveback() use spin_unlock_irqrestore() and spin_lock_irqsave(), but I would need to pass the flags to it somehow. Also, I am not sure how that would influence other drivers using musb. -- Hubert Wiśniewski <hubert.wisniewski.25632@xxxxxxxxx>
