On Sun, Mar 19, 2017 at 09:09:38PM -0700, Cong Wang wrote: > On Sat, Mar 18, 2017 at 9:03 PM, Kaiwen Xu <kaiwen...@hulu.com> wrote: > > On Sat, Mar 18, 2017 at 08:49:43PM -0700, Cong Wang wrote: > >> On Sat, Mar 18, 2017 at 6:48 PM, Kevin Xu <kaiwen...@hulu.com> wrote: > >> > In some rare cases, inet_sk_rx_dst_set() may be called multiple times > >> > on the same dst, causing double refcounting. Eventually, it > >> > prevents net_device to be destroyed. The bug manifested as > >> > > >> > unregister_netdevice: waiting for lo to become free. Usage count = 1 > >> > > >> > in the kernel log, preventing new network namespace creation. > >> > > >> > Signed-off-by: Kevin Xu <kaiwen...@hulu.com> > >> > >> Don't know why you don't follow the discussion on your v1... > >> > >> It is protected by bh_lock_sock(), so your patch is not needed > >> at all. > >> > >> Read net/ipv4/udp.c: > >> > >> 1762 /* For TCP sockets, sk_rx_dst is protected by socket lock > >> 1763 * For UDP, we use xchg() to guard against concurrent changes. > >> 1764 */ > > > > I probably misunderstood. Do you mean v2 patch is actually not needed or > > the whole workaround is not necessary? > > Your patch, no matter v1 or v2, is not needed because we use > bh_lock_sock() to serialize inet_sk_rx_dst_set(), unless you find > a case where we miss the bh_lock_sock(), but you don't say it in > your changelog. "some rare cases" is not enough to justify this bug.
I see, thanks for your explanation! I will try to dig in more to see if I can find the root cause.
