[PATCH] ugen_destroy_devnodes panic

Peter Pentchev roam at ringlet.net
Tue Jan 4 19:19:36 GMT 2005


I am getting reproducible panics on RELENG_5 with ugen and my camera,
Canon PowerShot A80.  The problem seems to be that ugen_set_config()
calls ugen_destroy_devnodes() twice, and ugen_destroy_devnodes() may get
to operate on the same sc's and the same devs, thus calling
destroy_dev() on an already destroyed endpoint device.  My first hunch
was to comment out the first ugen_destroy_devnodes() call in
ugen_set_config(), but then I realized that it might be necessary to
make sure no one else tries to open a ugen endpoint while it is being
marked for destruction.

What do you think about the following patch which makes
ugen_destroy_devnodes() zero out the dev pointer for each destroyed
device, so that it never attempts to destroy the same device twice?  Am
I right to think that after this routine is called, no one should use
the device endpoint that it freed?


Index: src/sys/dev/usb/ugen.c
RCS file: /home/ncvs/src/sys/dev/usb/ugen.c,v
retrieving revision
diff -u -r1.88.2.2 ugen.c
--- src/sys/dev/usb/ugen.c	31 Dec 2004 08:01:48 -0000
+++ src/sys/dev/usb/ugen.c	4 Jan 2005 18:20:39 -0000
@@ -283,7 +283,7 @@
 ugen_destroy_devnodes(struct ugen_softc *sc)
 	int endptno;
-	struct cdev *dev;
+	struct cdev **pdev;
 	/* destroy all devices for the other (existing) endpoints as well */
 	for (endptno = 1; endptno < USB_MAX_ENDPOINTS; endptno++) {
@@ -298,10 +298,13 @@
 			 * of the structs is populated.
 			if (sc->sc_endpoints[endptno][IN].sc != NULL)
-				dev = sc->sc_endpoints[endptno][IN].dev;
+				pdev = &sc->sc_endpoints[endptno][IN].dev;
-				dev = sc->sc_endpoints[endptno][OUT].dev;
-			destroy_dev(dev);
+				pdev = &sc->sc_endpoints[endptno][OUT].dev;
+			if (*pdev == NULL)
+				continue;
+			destroy_dev(*pdev);
+			*pdev = NULL;

Peter Pentchev	roam at ringlet.net    roam at cnsys.bg    roam at FreeBSD.org
PGP key:	http://people.FreeBSD.org/~roam/roam.key.asc
Key fingerprint	FDBA FD79 C26F 3C51 C95E  DF9E ED18 B68D 1619 4553
This sentence is false.
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