BTW when using the udlfb driver as a console, I've got this warning. vt_console_print takes a spinlock and then calls the framebuffer driver that sleeps.
The question is - whose fault is this? Could the console code somehow be told to print characters without holding a spinlock? Or does it mean that framebuffer drivers can't sleep?
udlfb communicates through USB, so the sleeping is inevitable.
Mikulas
BUG: sleeping function called from invalid context at mm/slab.h:421 in_atomic(): 1, irqs_disabled(): 0, pid: 430, name: kworker/2:3 6 locks held by kworker/2:3/430: #0: 000000001301127e ( (wq_completion)"events"){....} , at: process_one_work+0x17c/0x3a8 #1: 00000000beacc951 ( (work_completion)(&(&dlfb->init_framebuffer_work)->work)){....} , at: process_one_work+0x17c/0x3a8 #2: 00000000a402f826 ( registration_lock){....} , at: register_framebuffer+0x28/0x2c0 [fb] #3: 0000000021cbe902 ( console_lock){....} , at: register_framebuffer+0x258/0x2c0 [fb] #4: 0000000096d51735 ( console_owner){....} , at: console_unlock+0x174/0x500 #5: 00000000faa7f206 ( printing_lock){....} , at: vt_console_print+0x60/0x3a0 Preemption disabled at: [<ffffff8008403130>] vt_console_print+0x60/0x3a0 CPU: 2 PID: 430 Comm: kworker/2:3 Not tainted 4.17.10-debug #3 Hardware name: Marvell Armada 8040 MacchiatoBin/Armada 8040 MacchiatoBin, BIOS EDK II Jul 30 2018 Workqueue: events dlfb_init_framebuffer_work [udlfb] Call trace: dump_backtrace+0x0/0x150 show_stack+0x14/0x20 dump_stack+0x8c/0xac ___might_sleep+0x140/0x170 __might_sleep+0x50/0x88 __kmalloc+0x1b0/0x270 xhci_urb_enqueue+0xa8/0x460 [xhci_hcd] usb_hcd_submit_urb+0xc0/0x998 [usbcore] usb_submit_urb+0x1e0/0x518 [usbcore] dlfb_submit_urb+0x38/0x98 [udlfb] dlfb_handle_damage.isra.4+0x1e0/0x210 [udlfb] dlfb_ops_imageblit+0x28/0x38 [udlfb] soft_cursor+0x15c/0x1d8 [fb] bit_cursor+0x324/0x510 [fb] fbcon_cursor+0x144/0x1a0 [fb] hide_cursor+0x38/0xa0 vt_console_print+0x334/0x3a0 console_unlock+0x274/0x500 register_framebuffer+0x22c/0x2c0 [fb] dlfb_init_framebuffer_work+0x1ec/0x2fc [udlfb] process_one_work+0x1e8/0x3a8 worker_thread+0x44/0x418 kthread+0x11c/0x120 ret_from_fork+0x10/0x18