d/freebsd-skq
1
0
Fork 0
Code Issues Pull Requests Packages Projects Releases Wiki Activity

Lock down global variables in if_tap (primarily, the tap softc list);

Browse Source 
add tapmtx, which protects globale variables.

Notes:

- The EBUSY check in MOD_UNLOAD may be subject to a race.  Moving the
  event handler unregister inside the mutex grab may prevent that race.

- Locking of global variables safely is now possible because tapclones
  is only modified when the module is loading or unloading, thanks to
  phk's recent chang to clone_setup().

- softc locking to follow.
This commit is contained in:
rwatson 2004-03-15 01:52:00 +00:00
parent e3a889945b
commit 420f21f752
1 changed files with 28 additions and 3 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

31
sys/net/if_tap.c
View File

@ -108,6 +108,12 @@ static struct cdevsw tap_cdevsw = {
.d_name = CDEV_NAME,
};
/*
* All global variables in if_tap.c are locked with tapmtx, with the
* exception of tapdebug, which is accessed unlocked; tapclones is
* static at runtime.
*/
static struct mtx tapmtx;
static int tapdebug = 0; /* debug flag */
static SLIST_HEAD(, tap_softc) taphead; /* first device */
static struct clonedevs *tapclones;
@ -138,23 +144,38 @@ tapmodevent(mod, type, data)
/* intitialize device */
mtx_init(&tapmtx, "tapmtx", NULL, MTX_DEF);
SLIST_INIT(&taphead);
clone_setup(&tapclones);
eh_tag = EVENTHANDLER_REGISTER(dev_clone, tapclone, 0, 1000);
if (eh_tag == NULL)
if (eh_tag == NULL) {
mtx_destroy(&tapmtx);
return (ENOMEM);
}
return (0);
case MOD_UNLOAD:
SLIST_FOREACH(tp, &taphead, tap_next)
if (tp->tap_flags & TAP_OPEN)
/*
* The EBUSY algorithm here can't quite atomically
* guarantee that this is race-free since we have to
* release the tap mtx to deregister the clone handler.
*/
mtx_lock(&tapmtx);
SLIST_FOREACH(tp, &taphead, tap_next) {
if (tp->tap_flags & TAP_OPEN) {
mtx_unlock(&tapmtx);
return (EBUSY);
}
}
mtx_unlock(&tapmtx);
EVENTHANDLER_DEREGISTER(dev_clone, eh_tag);
mtx_lock(&tapmtx);
while ((tp = SLIST_FIRST(&taphead)) != NULL) {
SLIST_REMOVE_HEAD(&taphead, tap_next);
mtx_unlock(&tapmtx);
ifp = &tp->tap_if;
@ -169,7 +190,9 @@ tapmodevent(mod, type, data)
splx(s);
free(tp, M_TAP);
mtx_lock(&tapmtx);
}
mtx_unlock(&tapmtx);
clone_cleanup(&tapclones);
break;
@ -246,7 +269,9 @@ tapcreate(dev)
/* allocate driver storage and create device */
MALLOC(tp, struct tap_softc *, sizeof(*tp), M_TAP, M_WAITOK | M_ZERO);
mtx_lock(&tapmtx);
SLIST_INSERT_HEAD(&taphead, tp, tap_next);
mtx_unlock(&tapmtx);
unit = dev2unit(dev);