net: add CONFIG_PCPU_DEV_REFCNT
I was working on a syzbot issue, claiming one device could not be
dismantled because its refcount was -1
unregister_netdevice: waiting for sit0 to become free. Usage count = -1
It would be nice if syzbot could trigger a warning at the time
this reference count became negative.
This patch adds CONFIG_PCPU_DEV_REFCNT options which defaults
to per cpu variables (as before this patch) on SMP builds.
v2: free_dev label in alloc_netdev_mqs() is moved to avoid
a compiler warning (-Wunused-label), as reported
by kernel test robot <lkp@intel.com>
Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/Kconfig b/net/Kconfig
index 0ead7ec..9c456acc 100644
--- a/net/Kconfig
+++ b/net/Kconfig
@@ -245,6 +245,14 @@
source "net/qrtr/Kconfig"
source "net/ncsi/Kconfig"
+config PCPU_DEV_REFCNT
+ bool "Use percpu variables to maintain network device refcount"
+ depends on SMP
+ default y
+ help
+ network device refcount are using per cpu variables if this option is set.
+ This can be forced to N to detect underflows (with a performance drop).
+
config RPS
bool
depends on SMP && SYSFS
