Re: Sleeping from invalid context in udlfb

On Wed, 1 Aug 2018, Geert Uytterhoeven wrote:

Hi Mikulas,

On Wed, Aug 1, 2018 at 12:59 PM Mikulas Patocka [off-list ref] wrote:

quoted

On Wed, 1 Aug 2018, Geert Uytterhoeven wrote:

quoted

On Tue, Jul 31, 2018 at 5:23 PM Mikulas Patocka [off-list ref] wrote:

quoted

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

This is sort of expected: you cannot do USB transfers from printk().

Gr{oetje,eeting}s,

                        Geert

So, should there be a framebuffer flag that prevents the console from
binding to it?

If I start the kernel with "console=ttyS0,115200", it doesn't try to bind
to the udlfb driver, but if I start it without this flag, it does and
crashes :-(

Your frame buffer driver should offload tasks that may sleep to e.g. a
workqueue.

Gr{oetje,eeting}s,

                        Geert

I can try to do this - but - taking a spinlock and copying 8MB framebuffer 
would damage scheduling latency even for PCI framebuffer drivers.

Mikulas