| Message ID | 1384917154-11049-1-git-send-email-ast@plumgrid.com |
|---|---|
| State | Accepted, archived |
| Delegated to: | David Miller |
| Headers | show |
From: Alexei Starovoitov <ast@plumgrid.com> Date: Tue, 19 Nov 2013 19:12:34 -0800 > CPUs can ask for local route via ip_route_input_noref() concurrently. > if nh_rth_input is not cached yet, CPUs will proceed to allocate > equivalent DSTs on 'lo' and then will try to cache them in nh_rth_input > via rt_cache_route() > Most of the time they succeed, but on occasion the following two lines: > orig = *p; > prev = cmpxchg(p, orig, rt); > in rt_cache_route() do race and one of the cpus fails to complete cmpxchg. > But ip_route_input_slow() doesn't check the return code of rt_cache_route(), > so dst is leaking. dst_destroy() is never called and 'lo' device > refcnt doesn't go to zero, which can be seen in the logs as: > unregister_netdevice: waiting for lo to become free. Usage count = 1 > Adding mdelay() between above two lines makes it easily reproducible. > Fix it similar to nh_pcpu_rth_output case. > > Fixes: d2d68ba9fe8b ("ipv4: Cache input routes in fib_info nexthops.") > Signed-off-by: Alexei Starovoitov <ast@plumgrid.com> > --- > > David, > > looks like caacf05e5ad1 ("ipv4: Properly purge netdev references on uncached routes.") > fixed the race for nexthop/rth_output, but missed it for rth_input. > I'm not sure what was the assumption why it's not needed there. > We're definitely seeing it every 12-24hr during nightly tests. > There are several bugs on ubuntu and debian forums with similar description. > Some were closed, since folks struggled to reproduce it. > It took us more than a month to debug it. > Please queue for stable. Your analysis is accurate and your fix is absolutely correct, applied and queued up for -stable, thanks! -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
diff --git a/net/ipv4/route.c b/net/ipv4/route.c index f428935..f8da282 100644 --- a/net/ipv4/route.c +++ b/net/ipv4/route.c @@ -1776,8 +1776,12 @@ local_input: rth->dst.error= -err; rth->rt_flags &= ~RTCF_LOCAL; } - if (do_cache) - rt_cache_route(&FIB_RES_NH(res), rth); + if (do_cache) { + if (unlikely(!rt_cache_route(&FIB_RES_NH(res), rth))) { + rth->dst.flags |= DST_NOCACHE; + rt_add_uncached_list(rth); + } + } skb_dst_set(skb, &rth->dst); err = 0; goto out;
CPUs can ask for local route via ip_route_input_noref() concurrently. if nh_rth_input is not cached yet, CPUs will proceed to allocate equivalent DSTs on 'lo' and then will try to cache them in nh_rth_input via rt_cache_route() Most of the time they succeed, but on occasion the following two lines: orig = *p; prev = cmpxchg(p, orig, rt); in rt_cache_route() do race and one of the cpus fails to complete cmpxchg. But ip_route_input_slow() doesn't check the return code of rt_cache_route(), so dst is leaking. dst_destroy() is never called and 'lo' device refcnt doesn't go to zero, which can be seen in the logs as: unregister_netdevice: waiting for lo to become free. Usage count = 1 Adding mdelay() between above two lines makes it easily reproducible. Fix it similar to nh_pcpu_rth_output case. Fixes: d2d68ba9fe8b ("ipv4: Cache input routes in fib_info nexthops.") Signed-off-by: Alexei Starovoitov <ast@plumgrid.com> --- David, looks like caacf05e5ad1 ("ipv4: Properly purge netdev references on uncached routes.") fixed the race for nexthop/rth_output, but missed it for rth_input. I'm not sure what was the assumption why it's not needed there. We're definitely seeing it every 12-24hr during nightly tests. There are several bugs on ubuntu and debian forums with similar description. Some were closed, since folks struggled to reproduce it. It took us more than a month to debug it. Please queue for stable. Alternative fix: rt_free(rth); goto local_input; imo is uglier. Just like rt_free(rth) followed by re-read of nh_rth_input and re-check_valid net/ipv4/route.c | 8 ++++++-- 1 file changed, 6 insertions(+), 2 deletions(-)