Re: [PATCH] media: em28xx: modules workqueue not inited for 2nd device

[Ezequiel Garcia <ezequiel@collabora.com>]

On Sun, 2019-08-11 at 06:11 +0100, Sean Young wrote:
> syzbot reports an error on flush_request_modules() for the second device.
> This workqueue was never initialised so simply remove the offending line.
> 
> usb 1-1: USB disconnect, device number 2
> em28xx 1-1:1.153: Disconnecting em28xx #1
> ------------[ cut here ]------------
> WARNING: CPU: 0 PID: 12 at kernel/workqueue.c:3031
> __flush_work.cold+0x2c/0x36 kernel/workqueue.c:3031
> Kernel panic - not syncing: panic_on_warn set ...
> CPU: 0 PID: 12 Comm: kworker/0:1 Not tainted 5.3.0-rc2+ #25
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS
> Google 01/01/2011
> Workqueue: usb_hub_wq hub_event
> Call Trace:
>   __dump_stack lib/dump_stack.c:77 [inline]
>   dump_stack+0xca/0x13e lib/dump_stack.c:113
>   panic+0x2a3/0x6da kernel/panic.c:219
>   __warn.cold+0x20/0x4a kernel/panic.c:576
>   report_bug+0x262/0x2a0 lib/bug.c:186
>   fixup_bug arch/x86/kernel/traps.c:179 [inline]
>   fixup_bug arch/x86/kernel/traps.c:174 [inline]
>   do_error_trap+0x12b/0x1e0 arch/x86/kernel/traps.c:272
>   do_invalid_op+0x32/0x40 arch/x86/kernel/traps.c:291
>   invalid_op+0x23/0x30 arch/x86/entry/entry_64.S:1026
> RIP: 0010:__flush_work.cold+0x2c/0x36 kernel/workqueue.c:3031
> Code: 9a 22 00 48 c7 c7 20 e4 c5 85 e8 d9 3a 0d 00 0f 0b 45 31 e4 e9 98 86
> ff ff e8 51 9a 22 00 48 c7 c7 20 e4 c5 85 e8 be 3a 0d 00 <0f> 0b 45 31 e4
> e9 7d 86 ff ff e8 36 9a 22 00 48 c7 c7 20 e4 c5 85
> RSP: 0018:ffff8881da20f720 EFLAGS: 00010286
> RAX: 0000000000000024 RBX: dffffc0000000000 RCX: 0000000000000000
> RDX: 0000000000000000 RSI: ffffffff8128a0fd RDI: ffffed103b441ed6
> RBP: ffff8881da20f888 R08: 0000000000000024 R09: fffffbfff11acd9a
> R10: fffffbfff11acd99 R11: ffffffff88d66ccf R12: 0000000000000000
> R13: 0000000000000001 R14: ffff8881c6685df8 R15: ffff8881d2a85b78
>   flush_request_modules drivers/media/usb/em28xx/em28xx-cards.c:3325 [inline]
>   em28xx_usb_disconnect.cold+0x280/0x2a6
> drivers/media/usb/em28xx/em28xx-cards.c:4023
>   usb_unbind_interface+0x1bd/0x8a0 drivers/usb/core/driver.c:423
>   __device_release_driver drivers/base/dd.c:1120 [inline]
>   device_release_driver_internal+0x404/0x4c0 drivers/base/dd.c:1151
>   bus_remove_device+0x2dc/0x4a0 drivers/base/bus.c:556
>   device_del+0x420/0xb10 drivers/base/core.c:2288
>   usb_disable_device+0x211/0x690 drivers/usb/core/message.c:1237
>   usb_disconnect+0x284/0x8d0 drivers/usb/core/hub.c:2199
>   hub_port_connect drivers/usb/core/hub.c:4949 [inline]
>   hub_port_connect_change drivers/usb/core/hub.c:5213 [inline]
>   port_event drivers/usb/core/hub.c:5359 [inline]
>   hub_event+0x1454/0x3640 drivers/usb/core/hub.c:5441
>   process_one_work+0x92b/0x1530 kernel/workqueue.c:2269
>   process_scheduled_works kernel/workqueue.c:2331 [inline]
>   worker_thread+0x7ab/0xe20 kernel/workqueue.c:2417
>   kthread+0x318/0x420 kernel/kthread.c:255
>   ret_from_fork+0x24/0x30 arch/x86/entry/entry_64.S:352
> Kernel Offset: disabled
> Rebooting in 86400 seconds..
> 
> Reported-by: syzbot+b7f57261c521087d89bb@syzkaller.appspotmail.com
> Signed-off-by: Sean Young <sean@mess.org>

I reviewed the syzbot report, but was left head-scratching and
failing to see how the module-loading worker was supposed to be used :-)

Reviewed-by: Ezequiel Garcia <ezequiel@collabora.com>

Also, this seems a bug, so how about this tag?

Fixes: be7fd3c3a8c5e ("media: em28xx: Hauppauge DualHD second tuner functionality)

> ---
>  drivers/media/usb/em28xx/em28xx-cards.c | 1 -
>  1 file changed, 1 deletion(-)
> 
> diff --git a/drivers/media/usb/em28xx/em28xx-cards.c b/drivers/media/usb/em28xx/em28xx-cards.c
> index 6e33782c3ca6..5983e72a0622 100644
> --- a/drivers/media/usb/em28xx/em28xx-cards.c
> +++ b/drivers/media/usb/em28xx/em28xx-cards.c
> @@ -4019,7 +4019,6 @@ static void em28xx_usb_disconnect(struct usb_interface *intf)
>  		dev->dev_next->disconnected = 1;
>  		dev_info(&dev->intf->dev, "Disconnecting %s\n",
>  			 dev->dev_next->name);
> -		flush_request_modules(dev->dev_next);
>  	}
>  
>  	dev->disconnected = 1;