6.6-stable review patch. If anyone has any objections, please let me know.
------------------
From: Amit Cohen amcohen@nvidia.com
[ Upstream commit 62531a1effa87bdab12d5104015af72e60d926ff ]
A blocking notification chain uses a read-write semaphore to protect the integrity of the chain. The semaphore is acquired for writing when adding / removing notifiers to / from the chain and acquired for reading when traversing the chain and informing notifiers about an event.
In case of the blocking switchdev notification chain, recursive notifications are possible which leads to the semaphore being acquired twice for reading and to lockdep warnings being generated [1].
Specifically, this can happen when the bridge driver processes a SWITCHDEV_BRPORT_UNOFFLOADED event which causes it to emit notifications about deferred events when calling switchdev_deferred_process().
Fix this by converting the notification chain to a raw notification chain in a similar fashion to the netdev notification chain. Protect the chain using the RTNL mutex by acquiring it when modifying the chain. Events are always informed under the RTNL mutex, but add an assertion in call_switchdev_blocking_notifiers() to make sure this is not violated in the future.
Maintain the "blocking" prefix as events are always emitted from process context and listeners are allowed to block.
[1]: WARNING: possible recursive locking detected 6.14.0-rc4-custom-g079270089484 #1 Not tainted -------------------------------------------- ip/52731 is trying to acquire lock: ffffffff850918d8 ((switchdev_blocking_notif_chain).rwsem){++++}-{4:4}, at: blocking_notifier_call_chain+0x58/0xa0
but task is already holding lock: ffffffff850918d8 ((switchdev_blocking_notif_chain).rwsem){++++}-{4:4}, at: blocking_notifier_call_chain+0x58/0xa0
other info that might help us debug this: Possible unsafe locking scenario: CPU0 ---- lock((switchdev_blocking_notif_chain).rwsem); lock((switchdev_blocking_notif_chain).rwsem);
*** DEADLOCK *** May be due to missing lock nesting notation 3 locks held by ip/52731: #0: ffffffff84f795b0 (rtnl_mutex){+.+.}-{4:4}, at: rtnl_newlink+0x727/0x1dc0 #1: ffffffff8731f628 (&net->rtnl_mutex){+.+.}-{4:4}, at: rtnl_newlink+0x790/0x1dc0 #2: ffffffff850918d8 ((switchdev_blocking_notif_chain).rwsem){++++}-{4:4}, at: blocking_notifier_call_chain+0x58/0xa0
stack backtrace: ... ? __pfx_down_read+0x10/0x10 ? __pfx_mark_lock+0x10/0x10 ? __pfx_switchdev_port_attr_set_deferred+0x10/0x10 blocking_notifier_call_chain+0x58/0xa0 switchdev_port_attr_notify.constprop.0+0xb3/0x1b0 ? __pfx_switchdev_port_attr_notify.constprop.0+0x10/0x10 ? mark_held_locks+0x94/0xe0 ? switchdev_deferred_process+0x11a/0x340 switchdev_port_attr_set_deferred+0x27/0xd0 switchdev_deferred_process+0x164/0x340 br_switchdev_port_unoffload+0xc8/0x100 [bridge] br_switchdev_blocking_event+0x29f/0x580 [bridge] notifier_call_chain+0xa2/0x440 blocking_notifier_call_chain+0x6e/0xa0 switchdev_bridge_port_unoffload+0xde/0x1a0 ...
Fixes: f7a70d650b0b6 ("net: bridge: switchdev: Ensure deferred event delivery on unoffload") Signed-off-by: Amit Cohen amcohen@nvidia.com Reviewed-by: Ido Schimmel idosch@nvidia.com Reviewed-by: Simon Horman horms@kernel.org Reviewed-by: Vladimir Oltean olteanv@gmail.com Tested-by: Vladimir Oltean olteanv@gmail.com Link: https://patch.msgid.link/20250305121509.631207-1-amcohen@nvidia.com Signed-off-by: Paolo Abeni pabeni@redhat.com Signed-off-by: Sasha Levin sashal@kernel.org --- net/switchdev/switchdev.c | 25 ++++++++++++++++++------- 1 file changed, 18 insertions(+), 7 deletions(-)
diff --git a/net/switchdev/switchdev.c b/net/switchdev/switchdev.c index c9189a970eec3..fb0e65c89525d 100644 --- a/net/switchdev/switchdev.c +++ b/net/switchdev/switchdev.c @@ -381,7 +381,7 @@ bool switchdev_port_obj_act_is_deferred(struct net_device *dev, EXPORT_SYMBOL_GPL(switchdev_port_obj_act_is_deferred);
static ATOMIC_NOTIFIER_HEAD(switchdev_notif_chain); -static BLOCKING_NOTIFIER_HEAD(switchdev_blocking_notif_chain); +static RAW_NOTIFIER_HEAD(switchdev_blocking_notif_chain);
/** * register_switchdev_notifier - Register notifier @@ -427,17 +427,27 @@ EXPORT_SYMBOL_GPL(call_switchdev_notifiers);
int register_switchdev_blocking_notifier(struct notifier_block *nb) { - struct blocking_notifier_head *chain = &switchdev_blocking_notif_chain; + struct raw_notifier_head *chain = &switchdev_blocking_notif_chain; + int err; + + rtnl_lock(); + err = raw_notifier_chain_register(chain, nb); + rtnl_unlock();
- return blocking_notifier_chain_register(chain, nb); + return err; } EXPORT_SYMBOL_GPL(register_switchdev_blocking_notifier);
int unregister_switchdev_blocking_notifier(struct notifier_block *nb) { - struct blocking_notifier_head *chain = &switchdev_blocking_notif_chain; + struct raw_notifier_head *chain = &switchdev_blocking_notif_chain; + int err;
- return blocking_notifier_chain_unregister(chain, nb); + rtnl_lock(); + err = raw_notifier_chain_unregister(chain, nb); + rtnl_unlock(); + + return err; } EXPORT_SYMBOL_GPL(unregister_switchdev_blocking_notifier);
@@ -445,10 +455,11 @@ int call_switchdev_blocking_notifiers(unsigned long val, struct net_device *dev, struct switchdev_notifier_info *info, struct netlink_ext_ack *extack) { + ASSERT_RTNL(); info->dev = dev; info->extack = extack; - return blocking_notifier_call_chain(&switchdev_blocking_notif_chain, - val, info); + return raw_notifier_call_chain(&switchdev_blocking_notif_chain, + val, info); } EXPORT_SYMBOL_GPL(call_switchdev_blocking_notifiers);