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
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