kern/129053: lock order reversal
huntting at glarp.com
Fri Nov 21 08:40:02 PST 2008
>Synopsis: lock order reversal
>Arrival-Date: Fri Nov 21 16:40:02 UTC 2008
>Originator: Brad Huntting
FreeBSD spork.glarp.com 7.1-PRERELEASE FreeBSD 7.1-PRERELEASE #4: Thu Nov 13 11:34:12 MST 2008 root at spork.glarp.com:/usr/src/sys/i386/compile/SPORK i386
My device driver (a proprietary USB device called 'scmicro') appears to have tickled a lock order reversal. When witness.watch is enabled, all goes well until my driver detach()es. At which point my system panics with:
lock order reversal:
1st 0xc0c932a0 syscons video lock (syscons video lock) @ dev/syscons/syscons.c:2534
2nd 0xc0c23400 sched lock 0 (sched lock) @ kern/kern_clock.c:286
panic: blockable sleep lock (sleep mutex) sellck @ kern/sys_generic.c:1127
My driver creates two taskqueue(9) threads in attach() and destroys them in detach(). It has 4 mutexes which it uses to protect it's own data structures. In addition, it holds Giant around any code section which calls usb functions. With the exception of wakeup(9), cv_signal(9), cv_destroy(9) and taskqueue_enqueue_fast(), it always release it's own locks (except for Giant) before it calls external code.
Of course, this does not happen when my devices uses the ugen(4) driver.
Is this a known issue? Am I doing something wrong?
Sorry, my client wont let me release details of the driver.
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