Date: Fri, 21 Nov 2008 16:37:00 GMT From: Brad Huntting <huntting@glarp.com> To: freebsd-gnats-submit@FreeBSD.org Subject: kern/129053: lock order reversal Message-ID: <200811211637.mALGb0GK094872@www.freebsd.org> Resent-Message-ID: <200811211640.mALGe2HF096021@freefall.freebsd.org>
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>Number: 129053 >Category: kern >Synopsis: lock order reversal >Confidential: no >Severity: serious >Priority: medium >Responsible: freebsd-bugs >State: open >Quarter: >Keywords: >Date-Required: >Class: sw-bug >Submitter-Id: current-users >Arrival-Date: Fri Nov 21 16:40:02 UTC 2008 >Closed-Date: >Last-Modified: >Originator: Brad Huntting >Release: 7.1-PRERELEASE >Organization: >Environment: FreeBSD spork.glarp.com 7.1-PRERELEASE FreeBSD 7.1-PRERELEASE #4: Thu Nov 13 11:34:12 MST 2008 root@spork.glarp.com:/usr/src/sys/i386/compile/SPORK i386 >Description: 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? >How-To-Repeat: Sorry, my client wont let me release details of the driver. >Fix: >Release-Note: >Audit-Trail: >Unformatted:
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