Re: 2.6.21-mm2: HDAPS? BUG: at kernel/mutex.c:311

Andrew Morton
2007-05-12T00:54:06Z

On Fri, 11 May 2007 19:21:15 -0500
Matt Mackall <mpm@selenic.com> wrote:

> This just hit:
>
> [ 7.856000] usbcore: registered new interface driver usbhid
> [ 7.860000] BUG: at kernel/mutex.c:311 __mutex_trylock_slowpath()
> [ 7.868000] [<c0104584>] show_trace_log_lvl+0x1a/0x30
> [ 7.872000] [<c0105196>] show_trace+0x12/0x14
> [ 7.876000] [<c0105222>] dump_stack+0x15/0x17
> [ 7.880000] [<c03cd4c8>] mutex_trylock+0x56/0x15a
> [ 7.888000] [<c03172c5>] hdaps_mousedev_poll+0x10/0xcb
> [ 7.892000] [<c011f8c5>] run_timer_softirq+0x10e/0x16f
> [ 7.896000] [<c011cabc>] __do_softirq+0x5d/0xc0
> [ 7.900000] [<c0105c88>] do_softirq+0x6e/0xf0
> [ 7.904000] [<c011ca22>] irq_exit+0x3e/0x7b
> [ 7.912000] [<c0105da7>] do_IRQ+0x9d/0xb2
> [ 7.916000] [<c01040fa>] common_interrupt+0x2e/0x34
> [ 7.920000] [<c0118e5f>] printk+0x1b/0x1d
> [ 7.924000] [<c02f2f96>] usb_register_driver+0xa0/0xe5
> [ 7.928000] [<c0525018>] hid_init+0x28/0x51
> [ 7.932000] [<c050e6c4>] kernel_init+0xbc/0x23e
> [ 7.940000] [<c010420f>] kernel_thread_helper+0x7/0x10
> [ 7.944000] =======================
> [ 7.948000] drivers/hid/usbhid/hid-core.c: v2.6:USB HID core driver
>
> Looks like it's triggered by the HDAPS driver.
>

It's complaining about a mutex_trylock() being run from irq context.

And indeed that's buggy - the non-debug version of spin_lock_mutex() is not
irq-safe.

I'd say that's pretty dumb of the mutex interface, really. Doing a
mutex_trylock() should be OK from all contexts.

This is caused by a recent semaphore->mutex conversion and it's in mainline
now.

Ho hum. I suppose a suitable workaround would be to convert hdaps_mtx back
into a semaphore. ug.