WARNING in em28xx_usb_disconnect

[syzbot]

Hello,

syzbot found the following crash on:

HEAD commit: e96407b4 usb-fuzzer: main usb gadget fuzzer driver
git tree: https://github.com/google/kasan.git usb-fuzzer
console output: https://syzkaller.appspot.com/x/log.txt?x=15ef3cba600000
kernel config: https://syzkaller.appspot.com/x/.config?x=cfa2c18fb6a8068e
dashboard link: https://syzkaller.appspot.com/bug?extid=b7f57261c521087d89bb
compiler: gcc (GCC) 9.0.0 20181231 (experimental)
syz repro: https://syzkaller.appspot.com/x/repro.syz?x=16ceae36600000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=12816f26600000

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+b7f572...@syzkaller.appspotmail.com

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..


---
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[Sean Young]

syzbot reports an error on flush_request_modules() for the second device.
This workqueue was never initialised so simply remove the offending line.

Reported-by: syzbot+b7f572...@syzkaller.appspotmail.com
Signed-off-by: Sean Young <se...@mess.org>
---
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;
--
2.21.0

[Ezequiel Garcia]

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 <ezeq...@collabora.com>

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

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

[Sean Young]

Thank you for the review and yes it does need that tag.

Thanks
sean

[Sean Young]

Hi Brad,

On Mon, Aug 12, 2019 at 10:21:39AM -0300, Ezequiel Garcia wrote:

Would you mind reviewing this change please Brad? You added the dual_ts
feature to the driver so it would be good to have your view on this.

Thanks
Sean

[Brad Love]

Hey Sean,

Hmmm. I've never encountered this oops, nor had it reported to me. Looks
like the second device indeed never calls request_modules, and when I
did the cleanup I just duplicated all the teardown. Since everything
works without the second workqueue already, I don't think the second
device needs to initialize it's own. So, I think your solution is proper.


Reviewed-by: Brad Love <br...@nextdimension.cc>

[Sean Young]

Hi Brad,

Great, thank you!

If I understand this correctly, then if you build your kernel with KASAN
and UBSAN then I _think_ this is caught.

Thanks
Sean