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

[Joshua Washington <joshwash@google.com>]

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>
---
 drivers/net/ethernet/google/gve/gve_main.c |  4 ++--
 include/net/xdp.h                          |  3 +++
 net/core/xdp.c                             | 25 ++++++++++++++++++----
 3 files changed, 26 insertions(+), 6 deletions(-)

diff --git a/drivers/net/ethernet/google/gve/gve_main.c b/drivers/net/ethernet/google/gve/gve_main.c
index 8aaac9101377..446e4b6fd3f1 100644
--- a/drivers/net/ethernet/google/gve/gve_main.c
+++ b/drivers/net/ethernet/google/gve/gve_main.c
@@ -1830,7 +1830,7 @@ static void gve_turndown(struct gve_priv *priv)
 	/* Stop tx queues */
 	netif_tx_disable(priv->dev);
 
-	xdp_features_clear_redirect_target(priv->dev);
+	xdp_features_clear_redirect_target_locked(priv->dev);
 
 	gve_clear_napi_enabled(priv);
 	gve_clear_report_stats(priv);
@@ -1902,7 +1902,7 @@ static void gve_turnup(struct gve_priv *priv)
 	}
 
 	if (priv->tx_cfg.num_xdp_queues && gve_supports_xdp_xmit(priv))
-		xdp_features_set_redirect_target(priv->dev, false);
+		xdp_features_set_redirect_target_locked(priv->dev, false);
 
 	gve_set_napi_enabled(priv);
 }
diff --git a/include/net/xdp.h b/include/net/xdp.h
index 20e41b5ff319..b40f1f96cb11 100644
--- a/include/net/xdp.h
+++ b/include/net/xdp.h
@@ -618,7 +618,10 @@ bool bpf_dev_bound_kfunc_id(u32 btf_id);
 void xdp_set_features_flag(struct net_device *dev, xdp_features_t val);
 void xdp_set_features_flag_locked(struct net_device *dev, xdp_features_t val);
 void xdp_features_set_redirect_target(struct net_device *dev, bool support_sg);
+void xdp_features_set_redirect_target_locked(struct net_device *dev,
+					     bool support_sg);
 void xdp_features_clear_redirect_target(struct net_device *dev);
+void xdp_features_clear_redirect_target_locked(struct net_device *dev);
 #else
 static inline u32 bpf_xdp_metadata_kfunc_id(int id) { return 0; }
 static inline bool bpf_dev_bound_kfunc_id(u32 btf_id) { return false; }
diff --git a/net/core/xdp.c b/net/core/xdp.c
index a014df88620c..ea819764ae39 100644
--- a/net/core/xdp.c
+++ b/net/core/xdp.c
@@ -1014,21 +1014,38 @@ void xdp_set_features_flag(struct net_device *dev, xdp_features_t val)
 }
 EXPORT_SYMBOL_GPL(xdp_set_features_flag);
 
-void xdp_features_set_redirect_target(struct net_device *dev, bool support_sg)
+void xdp_features_set_redirect_target_locked(struct net_device *dev,
+					     bool support_sg)
 {
 	xdp_features_t val = (dev->xdp_features | NETDEV_XDP_ACT_NDO_XMIT);
 
 	if (support_sg)
 		val |= NETDEV_XDP_ACT_NDO_XMIT_SG;
-	xdp_set_features_flag(dev, val);
+	xdp_set_features_flag_locked(dev, val);
+}
+EXPORT_SYMBOL_GPL(xdp_features_set_redirect_target_locked);
+
+void xdp_features_set_redirect_target(struct net_device *dev, bool support_sg)
+{
+	netdev_lock(dev);
+	xdp_features_set_redirect_target_locked(dev, support_sg);
+	netdev_unlock(dev);
 }
 EXPORT_SYMBOL_GPL(xdp_features_set_redirect_target);
 
-void xdp_features_clear_redirect_target(struct net_device *dev)
+void xdp_features_clear_redirect_target_locked(struct net_device *dev)
 {
 	xdp_features_t val = dev->xdp_features;
 
 	val &= ~(NETDEV_XDP_ACT_NDO_XMIT | NETDEV_XDP_ACT_NDO_XMIT_SG);
-	xdp_set_features_flag(dev, val);
+	xdp_set_features_flag_locked(dev, val);
+}
+EXPORT_SYMBOL_GPL(xdp_features_clear_redirect_target_locked);
+
+void xdp_features_clear_redirect_target(struct net_device *dev)
+{
+	netdev_lock(dev);
+	xdp_features_clear_redirect_target_locked(dev);
+	netdev_unlock(dev);
 }
 EXPORT_SYMBOL_GPL(xdp_features_clear_redirect_target);
-- 
2.49.0.805.g082f7c87e0-goog