Re: [PATCH net-next] xdp: create locked/unlocked instances of xdp redirect target setters

[Stanislav Fomichev <stfomichev@gmail.com>]

On 04/21, Joshua Washington wrote:
> Commit 03df156dd3a6 ("xdp: double protect netdev->xdp_flags with
> netdev->lock") introduces the netdev lock to xdp_set_features_flag().
> The change includes a _locked version of the method, as it is possible
> for a driver to have already acquired the netdev lock before calling
> this helper. However, the same applies to
> xdp_features_(set|clear)_redirect_flags(), which ends up calling the
> unlocked version of xdp_set_features_flags() leading to deadlocks in
> GVE, which grabs the netdev lock as part of its suspend, reset, and
> shutdown processes:
> 
> [  833.265543] WARNING: possible recursive locking detected
> [  833.270949] 6.15.0-rc1 #6 Tainted: G            E
> [  833.276271] --------------------------------------------
> [  833.281681] systemd-shutdow/1 is trying to acquire lock:
> [  833.287090] ffff949d2b148c68 (&dev->lock){+.+.}-{4:4}, at: xdp_set_features_flag+0x29/0x90
> [  833.295470]
> [  833.295470] but task is already holding lock:
> [  833.301400] ffff949d2b148c68 (&dev->lock){+.+.}-{4:4}, at: gve_shutdown+0x44/0x90 [gve]
> [  833.309508]
> [  833.309508] other info that might help us debug this:
> [  833.316130]  Possible unsafe locking scenario:
> [  833.316130]
> [  833.322142]        CPU0
> [  833.324681]        ----
> [  833.327220]   lock(&dev->lock);
> [  833.330455]   lock(&dev->lock);
> [  833.333689]
> [  833.333689]  *** DEADLOCK ***
> [  833.333689]
> [  833.339701]  May be due to missing lock nesting notation
> [  833.339701]
> [  833.346582] 5 locks held by systemd-shutdow/1:
> [  833.351205]  #0: ffffffffa9c89130 (system_transition_mutex){+.+.}-{4:4}, at: __se_sys_reboot+0xe6/0x210
> [  833.360695]  #1: ffff93b399e5c1b8 (&dev->mutex){....}-{4:4}, at: device_shutdown+0xb4/0x1f0
> [  833.369144]  #2: ffff949d19a471b8 (&dev->mutex){....}-{4:4}, at: device_shutdown+0xc2/0x1f0
> [  833.377603]  #3: ffffffffa9eca050 (rtnl_mutex){+.+.}-{4:4}, at: gve_shutdown+0x33/0x90 [gve]
> [  833.386138]  #4: ffff949d2b148c68 (&dev->lock){+.+.}-{4:4}, at: gve_shutdown+0x44/0x90 [gve]
> 
> Introduce xdp_features_(set|clear)_redirect_target_locked() versions
> which assume that the netdev lock has already been acquired before
> setting the XDP feature flag and update GVE to use the locked version.
> 
> Cc: bpf@vger.kernel.org
> Fixes: 03df156dd3a6 ("xdp: double protect netdev->xdp_flags with netdev->lock")
> Tested-by: Mina Almasry <almasrymina@google.com>
> Reviewed-by: Willem de Bruijn <willemb@google.com>
> Reviewed-by: Harshitha Ramamurthy <hramamurthy@google.com>
> Signed-off-by: Joshua Washington <joshwash@google.com>

Acked-by: Stanislav Fomichev <sdf@fomichev.me>