Re: [PATCH] wifi: wext: Limit notifier event flushes to the device's netns

[Cosmin Ratiu <cratiu@nvidia.com>]

On Wed, 2026-10-21 at 17:41 +0300, Cosmin Ratiu wrote:
> With mlx5 netdev instance locking enabled, registering an IPoIB
> netdev
> calls the WEXT notifier while holding the instance mutex. Its call to
> wireless_nlevent_flush() takes net_rwsem to walk every namespace,
> completing the following lockdep dependency cycle:
> 
>   netdev instance mutex -> net_rwsem (read) -> GID table mutex
>     -> event_handler_rwsem (read) -> netdev instance mutex
> 
> RoCE GID enumeration takes the GID table mutex under net_rwsem. GID
> updates dispatch events under the table mutex, taking
> event_handler_rwsem.
> The IPoIB event handler takes the netdev instance mutex in
> ipoib_queue_work() to traverse child interfaces.
> 
> The all-namespace walk originated in the single global worker
> servicing
> per-namespace WEXT queues. The ordering fixes later reused that
> routine
> in netdevice notifiers to prevent delayed WEXT RTM_NEWLINK messages
> from
> following RTM_DELLINK or reporting stale interface flags. A notifier
> only
> needs to drain the affected device's namespace; there is no reason
> for it
> to walk and flush all namespaces.
> 
> Pass dev_net(dev) from both notifier callers and make the flush
> helper
> operate on that namespace. Keep the all-namespace walk and net_rwsem
> in
> the existing worker. This removes the instance-mutex -> net_rwsem
> dependency while retaining synchronous flushing from the notifiers.
> 
> It may seem strange that the fix for a lock cycle across multiple
> subsystems lies in a completely unrelated part of the code, but this
> seemed the most justified lock cycle edge to break.
> 
> Issue: 5331015
> Fixes: 8f7b00307bf1 ("net/mlx5e: Convert mlx5 netdevs to instance
> locking")
> Signed-off-by: Cosmin Ratiu <cratiu@nvidia.com>
> Change-Id: I98d7e77ffc9fa0ce72296d93c200da8fe1db378e

Sigh...Turns out I forgot to remove the "Issue" and the "Change-Id"
tags.
So there will be a v2 without those, but please let me know about the
rest of the patch until then...

Cosmin.