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net: switchdev: Convert blocking notification chain to a raw one 

JIRA: https://issues.redhat.com/browse/RHEL-75594

commit 62531a1effa87bdab12d5104015af72e60d926ff
Author: Amit Cohen <amcohen@nvidia.com>
Date:   Wed Mar 5 14:15:09 2025 +0200

    net: switchdev: Convert blocking notification chain to a raw one

    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: Mohammad Heib <mheib@redhat.com>
This commit is contained in:
Mohammad Heib 2025-07-21 13:42:55 +03:00
parent 6555d241ff
commit e7130338c4
1 changed files with 18 additions and 7 deletions
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25
net/switchdev/switchdev.c
View File

@ -472,7 +472,7 @@ 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
@ -518,17 +518,27 @@ 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;
return blocking_notifier_chain_register(chain, nb);
rtnl_lock();
err = raw_notifier_chain_register(chain, nb);
rtnl_unlock();
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);
@ -536,10 +546,11 @@ 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);