| Message ID | 20201204213900.234913-1-Joseph.Huang@garmin.com |
|---|---|
| State | Superseded |
| Headers | show |
| Series | [v2] bridge: Fix a deadlock when enabling multicast snooping | expand |
On 04/12/2020 23:39, Joseph Huang wrote: > When enabling multicast snooping, bridge module deadlocks on multicast_lock > if 1) IPv6 is enabled, and 2) there is an existing querier on the same L2 > network. > > The deadlock was caused by the following sequence: While holding the lock, > br_multicast_open calls br_multicast_join_snoopers, which eventually causes > IP stack to (attempt to) send out a Listener Report (in igmp6_join_group). > Since the destination Ethernet address is a multicast address, br_dev_xmit > feeds the packet back to the bridge via br_multicast_rcv, which in turn > calls br_multicast_add_group, which then deadlocks on multicast_lock. > > The fix is to move the call br_multicast_join_snoopers outside of the > critical section. This works since br_multicast_join_snoopers only deals > with IP and does not modify any multicast data structures of the bridge, > so there's no need to hold the lock. > > Steps to reproduce: > 1. sysctl net.ipv6.conf.all.force_mld_version=1 > 2. have another querier > 3. ip link set dev bridge type bridge mcast_snooping 0 && \ > ip link set dev bridge type bridge mcast_snooping 1 < deadlock > > > A typical call trace looks like the following: > > [ 936.251495] _raw_spin_lock+0x5c/0x68 > [ 936.255221] br_multicast_add_group+0x40/0x170 [bridge] > [ 936.260491] br_multicast_rcv+0x7ac/0xe30 [bridge] > [ 936.265322] br_dev_xmit+0x140/0x368 [bridge] > [ 936.269689] dev_hard_start_xmit+0x94/0x158 > [ 936.273876] __dev_queue_xmit+0x5ac/0x7f8 > [ 936.277890] dev_queue_xmit+0x10/0x18 > [ 936.281563] neigh_resolve_output+0xec/0x198 > [ 936.285845] ip6_finish_output2+0x240/0x710 > [ 936.290039] __ip6_finish_output+0x130/0x170 > [ 936.294318] ip6_output+0x6c/0x1c8 > [ 936.297731] NF_HOOK.constprop.0+0xd8/0xe8 > [ 936.301834] igmp6_send+0x358/0x558 > [ 936.305326] igmp6_join_group.part.0+0x30/0xf0 > [ 936.309774] igmp6_group_added+0xfc/0x110 > [ 936.313787] __ipv6_dev_mc_inc+0x1a4/0x290 > [ 936.317885] ipv6_dev_mc_inc+0x10/0x18 > [ 936.321677] br_multicast_open+0xbc/0x110 [bridge] > [ 936.326506] br_multicast_toggle+0xec/0x140 [bridge] > > Fixes: 4effd28c1245 ("bridge: join all-snoopers multicast address") > Signed-off-by: Joseph Huang <Joseph.Huang@garmin.com> > --- Hi, Thank you for fixing it up, a few minor nits below. Overall the patch looks good. > net/bridge/br_device.c | 6 ++++++ > net/bridge/br_multicast.c | 33 ++++++++++++++++++++++++--------- > net/bridge/br_private.h | 10 ++++++++++ > 3 files changed, 40 insertions(+), 9 deletions(-) > > diff --git a/net/bridge/br_device.c b/net/bridge/br_device.c > index 7730c8f3cb53..d3ea9d0779fb 100644 > --- a/net/bridge/br_device.c > +++ b/net/bridge/br_device.c > @@ -177,6 +177,9 @@ static int br_dev_open(struct net_device *dev) > br_stp_enable_bridge(br); > br_multicast_open(br); > > + if (br_opt_get(br, BROPT_MULTICAST_ENABLED)) > + br_multicast_join_snoopers(br); > + > return 0; > } > > @@ -197,6 +200,9 @@ static int br_dev_stop(struct net_device *dev) > br_stp_disable_bridge(br); > br_multicast_stop(br); > > + if (br_opt_get(br, BROPT_MULTICAST_ENABLED)) > + br_multicast_leave_snoopers(br); > + > netif_stop_queue(dev); > > return 0; > diff --git a/net/bridge/br_multicast.c b/net/bridge/br_multicast.c > index eae898c3cff7..426fe00db708 100644 > --- a/net/bridge/br_multicast.c > +++ b/net/bridge/br_multicast.c > @@ -3286,7 +3286,7 @@ static inline void br_ip6_multicast_join_snoopers(struct net_bridge *br) > } > #endif > > -static void br_multicast_join_snoopers(struct net_bridge *br) > +void br_multicast_join_snoopers(struct net_bridge *br) > { > br_ip4_multicast_join_snoopers(br); > br_ip6_multicast_join_snoopers(br); > @@ -3317,7 +3317,7 @@ static inline void br_ip6_multicast_leave_snoopers(struct net_bridge *br) > } > #endif > > -static void br_multicast_leave_snoopers(struct net_bridge *br) > +void br_multicast_leave_snoopers(struct net_bridge *br) > { > br_ip4_multicast_leave_snoopers(br); > br_ip6_multicast_leave_snoopers(br); > @@ -3336,9 +3336,6 @@ static void __br_multicast_open(struct net_bridge *br, > > void br_multicast_open(struct net_bridge *br) > { > - if (br_opt_get(br, BROPT_MULTICAST_ENABLED)) > - br_multicast_join_snoopers(br); > - > __br_multicast_open(br, &br->ip4_own_query); > #if IS_ENABLED(CONFIG_IPV6) > __br_multicast_open(br, &br->ip6_own_query); > @@ -3354,9 +3351,6 @@ void br_multicast_stop(struct net_bridge *br) > del_timer_sync(&br->ip6_other_query.timer); > del_timer_sync(&br->ip6_own_query.timer); > #endif > - > - if (br_opt_get(br, BROPT_MULTICAST_ENABLED)) > - br_multicast_leave_snoopers(br); > } > > void br_multicast_dev_del(struct net_bridge *br) > @@ -3487,6 +3481,8 @@ static void br_multicast_start_querier(struct net_bridge *br, > int br_multicast_toggle(struct net_bridge *br, unsigned long val) > { > struct net_bridge_port *port; > + bool join_snoopers = false; > + bool leave_snoopers = false; > We use reverse xmas tree order, longest to shortest, so these two have to be swapped, but one more related thing further below.. > spin_lock_bh(&br->multicast_lock); > if (!!br_opt_get(br, BROPT_MULTICAST_ENABLED) == !!val) > @@ -3495,7 +3491,7 @@ int br_multicast_toggle(struct net_bridge *br, unsigned long val) > br_mc_disabled_update(br->dev, val); > br_opt_toggle(br, BROPT_MULTICAST_ENABLED, !!val); > if (!br_opt_get(br, BROPT_MULTICAST_ENABLED)) { > - br_multicast_leave_snoopers(br); > + leave_snoopers = true; > goto unlock; > } > > @@ -3506,9 +3502,28 @@ int br_multicast_toggle(struct net_bridge *br, unsigned long val) > list_for_each_entry(port, &br->port_list, list) > __br_multicast_enable_port(port); > > + join_snoopers = true; > + > unlock: > spin_unlock_bh(&br->multicast_lock); > > + /* br_multicast_join_snoopers has the potential to cause > + * an MLD Report/Leave to be delivered to br_multicast_rcv, > + * which would in turn call br_multicast_add_group, which would > + * attempt to acquire multicast_lock. This function should be > + * called after the lock has been released to avoid deadlocks on > + * multicast_lock. > + * > + * br_multicast_leave_snoopers does not have the problem since > + * br_multicast_rcv first checks BROPT_MULTICAST_ENABLED, and > + * returns without calling br_multicast_ipv4/6_rcv if it's not > + * enabled. Moved both functions out just for symmetry. > + */ Nice comment, thanks! > + if (join_snoopers) > + br_multicast_join_snoopers(br); > + else if (leave_snoopers) > + br_multicast_leave_snoopers(br); If I'm not missing anything this can be just 1 bool like "change_snoopers" or something which if set to true will check BROPT_MULTICAST_ENABLED and act accordingly, i.e. if (change_snoopers) { if (br_opt_get(br, BROPT_MULTICAST_ENABLED)) br_multicast_join_snoopers(br); else br_multicast_leave_snoopers(br); } This is not really something critical, just an observation. Up to your preference if you decide to leave it with 2 bools. :-) Cheers, Nik > + > return 0; > } > > diff --git a/net/bridge/br_private.h b/net/bridge/br_private.h > index 345118e35c42..8424464186a6 100644 > --- a/net/bridge/br_private.h > +++ b/net/bridge/br_private.h > @@ -792,6 +792,8 @@ void br_multicast_del_port(struct net_bridge_port *port); > void br_multicast_enable_port(struct net_bridge_port *port); > void br_multicast_disable_port(struct net_bridge_port *port); > void br_multicast_init(struct net_bridge *br); > +void br_multicast_join_snoopers(struct net_bridge *br); > +void br_multicast_leave_snoopers(struct net_bridge *br); > void br_multicast_open(struct net_bridge *br); > void br_multicast_stop(struct net_bridge *br); > void br_multicast_dev_del(struct net_bridge *br); > @@ -969,6 +971,14 @@ static inline void br_multicast_init(struct net_bridge *br) > { > } > > +static inline void br_multicast_join_snoopers(struct net_bridge *br) > +{ > +} > + > +static inline void br_multicast_leave_snoopers(struct net_bridge *br) > +{ > +} > + > static inline void br_multicast_open(struct net_bridge *br) > { > } >
> > + if (join_snoopers) > > + br_multicast_join_snoopers(br); > > + else if (leave_snoopers) > > + br_multicast_leave_snoopers(br); > > If I'm not missing anything this can be just 1 bool like "change_snoopers" or > something which if set to true will check BROPT_MULTICAST_ENABLED and > act accordingly, i.e. > if (change_snoopers) { > if (br_opt_get(br, BROPT_MULTICAST_ENABLED)) > br_multicast_join_snoopers(br); > else > br_multicast_leave_snoopers(br); } > > This is not really something critical, just an observation. Up to your > preference if you decide to leave it with 2 bools. :-) > > Cheers, > Nik I wasn't sure how expensive the call to br_opt_get is, so I used a bool for each. I just checked and it seems that br_opt_get is probably just as cheap as a bool, so I'll change it according to what you suggested here. Thanks for your comments!! Thanks, Joseph
diff --git a/net/bridge/br_device.c b/net/bridge/br_device.c index 7730c8f3cb53..d3ea9d0779fb 100644 --- a/net/bridge/br_device.c +++ b/net/bridge/br_device.c @@ -177,6 +177,9 @@ static int br_dev_open(struct net_device *dev) br_stp_enable_bridge(br); br_multicast_open(br); + if (br_opt_get(br, BROPT_MULTICAST_ENABLED)) + br_multicast_join_snoopers(br); + return 0; } @@ -197,6 +200,9 @@ static int br_dev_stop(struct net_device *dev) br_stp_disable_bridge(br); br_multicast_stop(br); + if (br_opt_get(br, BROPT_MULTICAST_ENABLED)) + br_multicast_leave_snoopers(br); + netif_stop_queue(dev); return 0; diff --git a/net/bridge/br_multicast.c b/net/bridge/br_multicast.c index eae898c3cff7..426fe00db708 100644 --- a/net/bridge/br_multicast.c +++ b/net/bridge/br_multicast.c @@ -3286,7 +3286,7 @@ static inline void br_ip6_multicast_join_snoopers(struct net_bridge *br) } #endif -static void br_multicast_join_snoopers(struct net_bridge *br) +void br_multicast_join_snoopers(struct net_bridge *br) { br_ip4_multicast_join_snoopers(br); br_ip6_multicast_join_snoopers(br); @@ -3317,7 +3317,7 @@ static inline void br_ip6_multicast_leave_snoopers(struct net_bridge *br) } #endif -static void br_multicast_leave_snoopers(struct net_bridge *br) +void br_multicast_leave_snoopers(struct net_bridge *br) { br_ip4_multicast_leave_snoopers(br); br_ip6_multicast_leave_snoopers(br); @@ -3336,9 +3336,6 @@ static void __br_multicast_open(struct net_bridge *br, void br_multicast_open(struct net_bridge *br) { - if (br_opt_get(br, BROPT_MULTICAST_ENABLED)) - br_multicast_join_snoopers(br); - __br_multicast_open(br, &br->ip4_own_query); #if IS_ENABLED(CONFIG_IPV6) __br_multicast_open(br, &br->ip6_own_query); @@ -3354,9 +3351,6 @@ void br_multicast_stop(struct net_bridge *br) del_timer_sync(&br->ip6_other_query.timer); del_timer_sync(&br->ip6_own_query.timer); #endif - - if (br_opt_get(br, BROPT_MULTICAST_ENABLED)) - br_multicast_leave_snoopers(br); } void br_multicast_dev_del(struct net_bridge *br) @@ -3487,6 +3481,8 @@ static void br_multicast_start_querier(struct net_bridge *br, int br_multicast_toggle(struct net_bridge *br, unsigned long val) { struct net_bridge_port *port; + bool join_snoopers = false; + bool leave_snoopers = false; spin_lock_bh(&br->multicast_lock); if (!!br_opt_get(br, BROPT_MULTICAST_ENABLED) == !!val) @@ -3495,7 +3491,7 @@ int br_multicast_toggle(struct net_bridge *br, unsigned long val) br_mc_disabled_update(br->dev, val); br_opt_toggle(br, BROPT_MULTICAST_ENABLED, !!val); if (!br_opt_get(br, BROPT_MULTICAST_ENABLED)) { - br_multicast_leave_snoopers(br); + leave_snoopers = true; goto unlock; } @@ -3506,9 +3502,28 @@ int br_multicast_toggle(struct net_bridge *br, unsigned long val) list_for_each_entry(port, &br->port_list, list) __br_multicast_enable_port(port); + join_snoopers = true; + unlock: spin_unlock_bh(&br->multicast_lock); + /* br_multicast_join_snoopers has the potential to cause + * an MLD Report/Leave to be delivered to br_multicast_rcv, + * which would in turn call br_multicast_add_group, which would + * attempt to acquire multicast_lock. This function should be + * called after the lock has been released to avoid deadlocks on + * multicast_lock. + * + * br_multicast_leave_snoopers does not have the problem since + * br_multicast_rcv first checks BROPT_MULTICAST_ENABLED, and + * returns without calling br_multicast_ipv4/6_rcv if it's not + * enabled. Moved both functions out just for symmetry. + */ + if (join_snoopers) + br_multicast_join_snoopers(br); + else if (leave_snoopers) + br_multicast_leave_snoopers(br); + return 0; } diff --git a/net/bridge/br_private.h b/net/bridge/br_private.h index 345118e35c42..8424464186a6 100644 --- a/net/bridge/br_private.h +++ b/net/bridge/br_private.h @@ -792,6 +792,8 @@ void br_multicast_del_port(struct net_bridge_port *port); void br_multicast_enable_port(struct net_bridge_port *port); void br_multicast_disable_port(struct net_bridge_port *port); void br_multicast_init(struct net_bridge *br); +void br_multicast_join_snoopers(struct net_bridge *br); +void br_multicast_leave_snoopers(struct net_bridge *br); void br_multicast_open(struct net_bridge *br); void br_multicast_stop(struct net_bridge *br); void br_multicast_dev_del(struct net_bridge *br); @@ -969,6 +971,14 @@ static inline void br_multicast_init(struct net_bridge *br) { } +static inline void br_multicast_join_snoopers(struct net_bridge *br) +{ +} + +static inline void br_multicast_leave_snoopers(struct net_bridge *br) +{ +} + static inline void br_multicast_open(struct net_bridge *br) { }
When enabling multicast snooping, bridge module deadlocks on multicast_lock if 1) IPv6 is enabled, and 2) there is an existing querier on the same L2 network. The deadlock was caused by the following sequence: While holding the lock, br_multicast_open calls br_multicast_join_snoopers, which eventually causes IP stack to (attempt to) send out a Listener Report (in igmp6_join_group). Since the destination Ethernet address is a multicast address, br_dev_xmit feeds the packet back to the bridge via br_multicast_rcv, which in turn calls br_multicast_add_group, which then deadlocks on multicast_lock. The fix is to move the call br_multicast_join_snoopers outside of the critical section. This works since br_multicast_join_snoopers only deals with IP and does not modify any multicast data structures of the bridge, so there's no need to hold the lock. Steps to reproduce: 1. sysctl net.ipv6.conf.all.force_mld_version=1 2. have another querier 3. ip link set dev bridge type bridge mcast_snooping 0 && \ ip link set dev bridge type bridge mcast_snooping 1 < deadlock > A typical call trace looks like the following: [ 936.251495] _raw_spin_lock+0x5c/0x68 [ 936.255221] br_multicast_add_group+0x40/0x170 [bridge] [ 936.260491] br_multicast_rcv+0x7ac/0xe30 [bridge] [ 936.265322] br_dev_xmit+0x140/0x368 [bridge] [ 936.269689] dev_hard_start_xmit+0x94/0x158 [ 936.273876] __dev_queue_xmit+0x5ac/0x7f8 [ 936.277890] dev_queue_xmit+0x10/0x18 [ 936.281563] neigh_resolve_output+0xec/0x198 [ 936.285845] ip6_finish_output2+0x240/0x710 [ 936.290039] __ip6_finish_output+0x130/0x170 [ 936.294318] ip6_output+0x6c/0x1c8 [ 936.297731] NF_HOOK.constprop.0+0xd8/0xe8 [ 936.301834] igmp6_send+0x358/0x558 [ 936.305326] igmp6_join_group.part.0+0x30/0xf0 [ 936.309774] igmp6_group_added+0xfc/0x110 [ 936.313787] __ipv6_dev_mc_inc+0x1a4/0x290 [ 936.317885] ipv6_dev_mc_inc+0x10/0x18 [ 936.321677] br_multicast_open+0xbc/0x110 [bridge] [ 936.326506] br_multicast_toggle+0xec/0x140 [bridge] Fixes: 4effd28c1245 ("bridge: join all-snoopers multicast address") Signed-off-by: Joseph Huang <Joseph.Huang@garmin.com> --- net/bridge/br_device.c | 6 ++++++ net/bridge/br_multicast.c | 33 ++++++++++++++++++++++++--------- net/bridge/br_private.h | 10 ++++++++++ 3 files changed, 40 insertions(+), 9 deletions(-)