Re: usb/gadget: potential deadlock in gadgetfs_suspend

[Alan Stern]

On Fri, 9 Jun 2017, Andrey Konovalov wrote:

> On Fri, Jun 9, 2017 at 2:41 PM, Andrey Konovalov <andreyknvl@xxxxxxxxxx> wrote:
> > Hi,
> >
> > I'm getting some hangs while fuzzing the kernel with syzkaller.
> >
> > Possibly it happens during the execution of the following syzkaller program:
> >
> > mmap(&(0x7f0000000000/0xb90000)=nil, (0xb90000), 0x3, 0x32,
> > 0xffffffffffffffff, 0x0)
> > r0 = open$usb(&(0x7f0000001000)="2f6465762f6761646765742f64756d6d795f75646300",
> > 0xc002, 0x0)
> > r1 = open$usb(&(0x7f0000002000)="2f6465762f6761646765742f64756d6d795f75646300",
> > 0x1, 0x102)
> > write$usb(r1, &(0x7f0000003000)={0x0, {0x9, 0x2, 0x1b, 0x0, 0x5, 0x0,
> > 0x80, 0x8, 0x9, 0x4, 0x10000000, 0xfffffefffffffff9, 0x1, 0xff, 0x0,

I don't understand these large constants.  They're supposed to be __u8 
values.  Do they get truncated to the least significant byte?

> > 0x8, 0x80, [{0x9, 0x5, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0}]}, {0x12, 0x1,
> > 0x0, 0x0, 0x4b5, 0x7c, 0x0, 0x3, 0x4, 0x0, 0x8, 0xd686, 0x0, 0x1}},
> > 0x31)
> >
> > I haven't managed to get the exact same stack trace (or any at all
> > actually) while trying to reproduce the bug with this program, but the
> > kernel definitely hangs.

Can you get a usbmon trace for the test?  And can you enable debugging
for the usbcore module?

	echo "module usbcore =p" >/sys/kernel/debug/dynamic_debug/control

> > On commit b29794ec95c6856b316c2295904208bf11ffddd9 (4.12-rc4+) with
> > Alan's patch applied.
> >
> > gadgetfs: bound to dummy_udc driver
> > gadgetfs: suspended from state 2
> > INFO: rcu_sched detected stalls on CPUs/tasks:
> > 1-...: (0 ticks this GP) idle=966/140000000000000/0 softirq=37706/37706 fqs=5250
> > (detected by 2, t=21002 jiffies, g=26575, c=26574, q=183)
> > Sending NMI from CPU 2 to CPUs 1:
> > NMI backtrace for cpu 1
> > CPU: 1 PID: 1394 Comm: kworker/1:2 Not tainted 4.12.0-rc4+ #24
> > Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Bochs 01/01/2011
> > Workqueue: usb_hub_wq hub_event
> > task: ffff88003ebfb640 task.stack: ffffc900024fc000
> > RIP: 0010:rep_nop arch/x86/include/asm/processor.h:619 [inline]
> > RIP: 0010:cpu_relax arch/x86/include/asm/processor.h:624 [inline]
> > RIP: 0010:virt_spin_lock arch/x86/include/asm/qspinlock.h:63 [inline]
> > RIP: 0010:queued_spin_lock_slowpath+0x20/0x1a0 kernel/locking/qspinlock.c:421
> > RSP: 0018:ffffc900024ff9f0 EFLAGS: 00000002
> > RAX: 000000007d72e420 RBX: ffff88007d72e768 RCX: 0000000000010000
> > RDX: 0000000000000001 RSI: 000000007d72e420 RDI: ffff88007d72e768
> > RBP: ffffc900024ff9f0 R08: 0000000000000006 R09: 0000000000000020
> > R10: ffffc900024ffa50 R11: 0000000000d52301 R12: ffff88007da9c298
> > R13: 0000000000000000 R14: 0000000000000000 R15: ffffffff82cfc5a0
> > FS:  0000000000000000(0000) GS:ffff88003ed00000(0000) knlGS:0000000000000000
> > CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> > CR2: 00007f728a487000 CR3: 00000000371e6000 CR4: 00000000000006e0
> > Call Trace:
> >  __raw_spin_lock include/asm-generic/qspinlock.h:103 [inline]
> >  _raw_spin_lock+0x1c/0x20 kernel/locking/spinlock.c:151
> >  spin_lock include/linux/spinlock.h:299 [inline]
> >  gadgetfs_suspend+0x32/0x90 drivers/usb/gadget/legacy/inode.c:1684

Looks like it's waiting for the spinlock in gadgetfs_suspend.  Nothing 
else should be holding that lock.

Were any other tasks stalled?

> >  set_link_state+0x39c/0x440 drivers/usb/gadget/udc/dummy_hcd.c:455
> >  dummy_hub_control+0x3e7/0x650 drivers/usb/gadget/udc/dummy_hcd.c:2074
> >  rh_call_control drivers/usb/core/hcd.c:689 [inline]
> >  rh_urb_enqueue drivers/usb/core/hcd.c:846 [inline]
> >  usb_hcd_submit_urb+0x327/0xcf0 drivers/usb/core/hcd.c:1650
> >  usb_submit_urb+0x355/0x6f0 drivers/usb/core/urb.c:542
> >  usb_start_wait_urb+0x5f/0x110 drivers/usb/core/message.c:56
> >  usb_internal_control_msg drivers/usb/core/message.c:100 [inline]
> >  usb_control_msg+0xd9/0x120 drivers/usb/core/message.c:151
> >  usb_clear_port_feature+0x46/0x60 drivers/usb/core/hub.c:412
> >  hub_port_disable+0x65/0x1d0 drivers/usb/core/hub.c:4177
> >  hub_port_init+0x10a/0xee0 drivers/usb/core/hub.c:4648
> >  hub_port_connect drivers/usb/core/hub.c:4826 [inline]
> >  hub_port_connect_change drivers/usb/core/hub.c:4999 [inline]
> >  port_event drivers/usb/core/hub.c:5105 [inline]
> >  hub_event+0xa0b/0x16e0 drivers/usb/core/hub.c:5189
> >  process_one_work+0x1fb/0x4c0 kernel/workqueue.c:2097
> >  process_scheduled_works kernel/workqueue.c:2157 [inline]
> >  worker_thread+0x2ab/0x4c0 kernel/workqueue.c:2233
> >  kthread+0x140/0x160 kernel/kthread.c:231
> >  ret_from_fork+0x25/0x30 arch/x86/entry/entry_64.S:424
> > Code: 66 66 2e 0f 1f 84 00 00 00 00 00 55 48 89 e5 0f 1f 44 00 00 ba
> > 01 00 00 00 8b 07 85 c0 75 0a f0 0f b1 17 85 c0 75 f2 5d c3 f3 90 <eb>
> > ec 81 fe 00 01 00 00 0f 84 92 00 00 00 41 b8 01 01 00 00 b9

Alan Stern