Date: Wed, 27 Jun 2012 18:30:49 GMT From: Steven Hartland <steven.hartland@multiplay.co.uk> To: freebsd-gnats-submit@FreeBSD.org Subject: kern/169495: panic after cam scsi cd device loss (patch included) Message-ID: <201206271830.q5RIUnhd050617@red.freebsd.org> Resent-Message-ID: <201206271840.q5RIeAnl016509@freefall.freebsd.org>
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>Number: 169495
>Category: kern
>Synopsis: panic after cam scsi cd device loss (patch included)
>Confidential: no
>Severity: serious
>Priority: low
>Responsible: freebsd-bugs
>State: open
>Quarter:
>Keywords:
>Date-Required:
>Class: sw-bug
>Submitter-Id: current-users
>Arrival-Date: Wed Jun 27 18:40:10 UTC 2012
>Closed-Date:
>Last-Modified:
>Originator: Steven Hartland
>Release: 8.3-RELEASE
>Organization:
Multiplay
>Environment:
FreeBSD blade26.multiplay.co.uk 8.3-RELEASE-p3 FreeBSD 8.3-RELEASE-p3 #114: Wed Jun 27 17:26:53 UTC 2012 root@build:/usr/obj/usr/src/sys/MULTIPLAY amd64
>Description:
While testing a kernel patch we ended with a reproducable panic when disconnecting the IPMI cd device.
The panic is from the force panic in cam_periph_release_locked_buses on 8.3
panic("%s: release of %p when refcount is zero\n ", __func__, periph);
After much investigation it turns out cam/scsi_cd.c isn't testing the return from cam_periph_hold in cdclose.
>How-To-Repeat:
This is hard to repeat on a stock kernel as it seems to be very timing dependent but on our machine disconnecting the IPMI cd device causes the panic.
>Fix:
The fix is to test the return code from cam_periph_hold as done by the scsi da device, see patch attached.
Patch attached with submission follows:
--- /usr/src/sys/cam/scsi/scsi_cd.c.orig 2012-06-27 17:20:12.902599170 +0000
+++ /usr/src/sys/cam/scsi/scsi_cd.c 2012-06-27 17:39:11.567322238 +0000
@@ -1041,7 +1041,11 @@
softc = (struct cd_softc *)periph->softc;
cam_periph_lock(periph);
- cam_periph_hold(periph, PRIBIO);
+ if (cam_periph_hold(periph, PRIBIO) != 0) {
+ cam_periph_unlock(periph);
+ cam_periph_release(periph);
+ return (0);
+ }
if ((softc->flags & CD_FLAG_DISC_REMOVABLE) != 0)
cdprevent(periph, PR_ALLOW);
>Release-Note:
>Audit-Trail:
>Unformatted:
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