kmem leakage on tun/tap device removal
Kostik Belousov
kostikbel at gmail.com
Sat Feb 27 15:16:31 UTC 2010
On Sat, Feb 27, 2010 at 11:21:17AM +0200, Mikolaj Golub wrote:
> Hi,
>
> Recently I run some tests, which create/destroy tun interface in loop, and
> after several hours my system panicked with "kmem_map too small". It has
> appeared that tun (or tap) device does not free memory after the device
> destroy:
>
> zhuzha:/usr/src/sys/kern% sudo vmstat -m |grep 'Type\|DEVFS1'
> Type InUse MemUse HighUse Requests Size(s)
> DEVFS1 139 35K - 157 256
> zhuzha:/usr/src/sys/kern% sudo ifconfig tun0 create
> zhuzha:/usr/src/sys/kern% sudo vmstat -m |grep 'Type\|DEVFS1'
> Type InUse MemUse HighUse Requests Size(s)
> DEVFS1 140 35K - 159 256
> zhuzha:/usr/src/sys/kern% sudo ifconfig tun0 destroy
> zhuzha:/usr/src/sys/kern% sudo vmstat -m |grep 'Type\|DEVFS1'
> Type InUse MemUse HighUse Requests Size(s)
> DEVFS1 140 35K - 159 256
>
> And when running create/destroy in loop:
>
> Time Type InUse MemUse HighUse Requests Size(s)
> 09:20 DEVFS1 104 26K - 113 256
> 09:25 DEVFS1 8504 2126K - 16912 256
> 09:30 DEVFS1 31602 7901K - 63108 256
> 09:35 DEVFS1 54316 13579K - 108536 256
> 09:40 DEVFS1 77068 19267K - 154040 256
> 09:45 DEVFS1 99764 24941K - 199431 256
> 09:50 DEVFS1 122408 30602K - 244719 256
> 09:55 DEVFS1 144689 36173K - 289281 256
>
> It looks like the problem is that tun/tap_clone_create() calls make_dev() and
> then dev_ref(dev). make_dev() calls itself dev_refl(), so after device creating
> we have si_refcount == 2. But on device removal (tun/tap_clone_destroy())
> dev_rel() is never called, only destroy_dev(dev), which checks that
> si_refcount is still not zero and places the dev in dead_cdevsw.d_devs list.
>
> And running kgdb we can see the following picture:
>
> (kgdb) p *dead_cdevsw.d_devs.lh_first
> $2 = {__si_reserved = 0x0, si_flags = 0, si_atime = {tv_sec = 1267218482, tv_nsec = 0}, si_ctime = {
> tv_sec = 1267218482, tv_nsec = 0}, si_mtime = {tv_sec = 1267218482, tv_nsec = 0}, si_uid = 66,
> si_gid = 68, si_mode = 384, si_cred = 0x0, si_drv0 = 0, si_refcount = 1, si_list = {
> le_next = 0xcd183100, le_prev = 0xc0d90278}, si_clone = {le_next = 0x0, le_prev = 0xc5c83b50},
> si_children = {lh_first = 0x0}, si_siblings = {le_next = 0x0, le_prev = 0x0}, si_parent = 0x0,
> si_name = 0xcaadc278 "tun0", si_drv1 = 0x0, si_drv2 = 0x0, si_devsw = 0x0, si_iosize_max = 0,
> si_usecount = 0, si_threadcount = 0, __si_u = {__sid_snapdata = 0x0},
> __si_namebuf = "tun0", '\0' <repeats 59 times>}
> (kgdb) p *dead_cdevsw.d_devs.lh_first->si_list.le_next
> $3 = {__si_reserved = 0x0, si_flags = 0, si_atime = {tv_sec = 1267218421, tv_nsec = 0}, si_ctime = {
> tv_sec = 1267218421, tv_nsec = 0}, si_mtime = {tv_sec = 1267218421, tv_nsec = 0}, si_uid = 66,
> si_gid = 68, si_mode = 384, si_cred = 0x0, si_drv0 = 0, si_refcount = 1, si_list = {
> le_next = 0xcd183000, le_prev = 0xcaadc238}, si_clone = {le_next = 0x0, le_prev = 0xc5c83b50},
> si_children = {lh_first = 0x0}, si_siblings = {le_next = 0x0, le_prev = 0x0}, si_parent = 0x0,
> si_name = 0xcd183178 "tun0", si_drv1 = 0x0, si_drv2 = 0x0, si_devsw = 0x0, si_iosize_max = 0,
> si_usecount = 0, si_threadcount = 0, __si_u = {__sid_snapdata = 0x0},
> __si_namebuf = "tun0", '\0' <repeats 59 times>}
> ... and so on.
>
> Is dev_ref() needed in tun_clone_create() after make_dev() call? Can't it be
> safely removed as in the patch below? I have run some tests with the patch and
> it looks like it works for me.
CHEAPCLONE is unused too. Besides this, there are two races in
the clone handling. First is that dev_clone handlers shall use
make_dev_credf(MAKEDEV_REF) instead of make_dev/dev_ref. Second is that
module unload shall drain clone events.
Please test the patch below.
diff --git a/sys/net/if_tap.c b/sys/net/if_tap.c
index 950e96c..93801f1 100644
--- a/sys/net/if_tap.c
+++ b/sys/net/if_tap.c
@@ -192,10 +192,6 @@ tap_clone_create(struct if_clone *ifc, int unit, caddr_t params)
if (i) {
dev = make_dev(&tap_cdevsw, unit | extra,
UID_ROOT, GID_WHEEL, 0600, "%s%d", ifc->ifc_name, unit);
- if (dev != NULL) {
- dev_ref(dev);
- dev->si_flags |= SI_CHEAPCLONE;
- }
}
tapcreate(dev);
@@ -300,6 +296,7 @@ tapmodevent(module_t mod, int type, void *data)
EVENTHANDLER_DEREGISTER(dev_clone, eh_tag);
if_clone_detach(&tap_cloner);
if_clone_detach(&vmnet_cloner);
+ drain_dev_clone_events();
mtx_lock(&tapmtx);
while ((tp = SLIST_FIRST(&taphead)) != NULL) {
@@ -381,12 +378,8 @@ tapclone(void *arg, struct ucred *cred, char *name, int namelen, struct cdev **d
name = devname;
}
- *dev = make_dev(&tap_cdevsw, unit | extra,
- UID_ROOT, GID_WHEEL, 0600, "%s", name);
- if (*dev != NULL) {
- dev_ref(*dev);
- (*dev)->si_flags |= SI_CHEAPCLONE;
- }
+ *dev = make_dev_credf(MAKEDEV_REF, &tap_cdevsw, unit | extra,
+ cred, UID_ROOT, GID_WHEEL, 0600, "%s", name);
}
if_clone_create(name, namelen, NULL);
diff --git a/sys/net/if_tun.c b/sys/net/if_tun.c
index 37b5e70..1fa02ac 100644
--- a/sys/net/if_tun.c
+++ b/sys/net/if_tun.c
@@ -188,10 +188,6 @@ tun_clone_create(struct if_clone *ifc, int unit, caddr_t params)
/* No preexisting struct cdev *, create one */
dev = make_dev(&tun_cdevsw, unit,
UID_UUCP, GID_DIALER, 0600, "%s%d", ifc->ifc_name, unit);
- if (dev != NULL) {
- dev_ref(dev);
- dev->si_flags |= SI_CHEAPCLONE;
- }
}
tuncreate(ifc->ifc_name, dev);
@@ -237,12 +233,8 @@ tunclone(void *arg, struct ucred *cred, char *name, int namelen,
name = devname;
}
/* No preexisting struct cdev *, create one */
- *dev = make_dev(&tun_cdevsw, u,
+ *dev = make_dev_credf(MAKEDEV_REF, &tun_cdevsw, u, cred,
UID_UUCP, GID_DIALER, 0600, "%s", name);
- if (*dev != NULL) {
- dev_ref(*dev);
- (*dev)->si_flags |= SI_CHEAPCLONE;
- }
}
if_clone_create(name, namelen, NULL);
@@ -303,6 +295,7 @@ tunmodevent(module_t mod, int type, void *data)
case MOD_UNLOAD:
if_clone_detach(&tun_cloner);
EVENTHANDLER_DEREGISTER(dev_clone, tag);
+ drain_dev_clone_events();
mtx_lock(&tunmtx);
while ((tp = TAILQ_FIRST(&tunhead)) != NULL) {
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