Subject: [net 07/15] net/mlx5e: Fix deadlock in tc route query code

From: Saeed Mahameed <[email-masked]>
Date: Mon, 22 May 2023 22:42:34 -0700

From: Vlad Buslov <[email-masked]>

Cited commit causes ABBA deadlock[0] when peer flows are created while
holding the devcom rw semaphore. Due to peer flows offload implementation
the lock is taken much higher up the call chain and there is no obvious way
to easily fix the deadlock. Instead, since tc route query code needs the
peer eswitch structure only to perform a lookup in xarray and doesn't
perform any sleeping operations with it, refactor the code for lockless
execution in following ways:

- RCUify the devcom 'data' pointer. When resetting the pointer
synchronously wait for RCU grace period before returning. This is fine
since devcom is currently only used for synchronization of
pairing/unpairing of eswitches which is rare and already expensive as-is.

- Wrap all usages of 'paired' boolean in {READ|WRITE}_ONCE(). The flag has
already been used in some unlocked contexts without proper
annotations (e.g. users of mlx5_devcom_is_paired() function), but it wasn't
an issue since all relevant code paths checked it again after obtaining the
devcom semaphore. Now it is also used by mlx5_devcom_get_peer_data_rcu() as
"best effort" check to return NULL when devcom is being unpaired. Note that
while RCU read lock doesn't prevent the unpaired flag from being changed
concurrently it still guarantees that reader can continue to use 'data'.

- Refactor mlx5e_tc_query_route_vport() function to use new
mlx5_devcom_get_peer_data_rcu() API which fixes the deadlock.

[0]:

[  164.599612] ======================================================
[  164.600142] WARNING: possible circular locking dependency detected
[  164.600667] 6.3.0-rc3+ #1 Not tainted
[  164.601021] ------------------------------------------------------
[  164.601557] handler1/3456 is trying to acquire lock:
[  164.601998] ffff88811f1714b0 (&esw->offloads.encap_tbl_lock){+.+.}-{3:3}, at: mlx5e_attach_encap+0xd8/0x8b0 [mlx5_core]
[  164.603078]
               but task is already holding lock:
[  164.603617] ffff88810137fc98 (&comp->sem){++++}-{3:3}, at: mlx5_devcom_get_peer_data+0x37/0x80 [mlx5_core]
[  164.604459]
               which lock already depends on the new lock.

[  164.605190]
               the existing dependency chain (in reverse order) is:
[  164.605848]
               -> #1 (&comp->sem){++++}-{3:3}:
[  164.606380]        down_read+0x39/0x50
[  164.606772]        mlx5_devcom_get_peer_data+0x37/0x80 [mlx5_core]
[  164.607336]        mlx5e_tc_query_route_vport+0x86/0xc0 [mlx5_core]
[  164.607914]        mlx5e_tc_tun_route_lookup+0x1a4/0x1d0 [mlx5_core]
[  164.608495]        mlx5e_attach_decap_route+0xc6/0x1e0 [mlx5_core]
[  164.609063]        mlx5e_tc_add_fdb_flow+0x1ea/0x360 [mlx5_core]
[  164.609627]        __mlx5e_add_fdb_flow+0x2d2/0x430 [mlx5_core]
[  164.610175]        mlx5e_configure_flower+0x952/0x1a20 [mlx5_core]
[  164.610741]        tc_setup_cb_add+0xd4/0x200
[  164.611146]        fl_hw_replace_filter+0x14c/0x1f0 [cls_flower]
[  164.611661]        fl_change+0xc95/0x18a0 [cls_flower]
[  164.612116]        tc_new_tfilter+0x3fc/0xd20
[  164.612516]        rtnetlink_rcv_msg+0x418/0x5b0
[  164.612936]        netlink_rcv_skb+0x54/0x100
[  164.613339]        netlink_unicast+0x190/0x250
[  164.613746]        netlink_sendmsg+0x245/0x4a0
[  164.614150]        sock_sendmsg+0x38/0x60
[  164.614522]        ____sys_sendmsg+0x1d0/0x1e0
[  164.614934]        ___sys_sendmsg+0x80/0xc0
[  164.615320]        __sys_sendmsg+0x51/0x90
[  164.615701]        do_syscall_64+0x3d/0x90
[  164.616083]        entry_SYSCALL_64_after_hwframe+0x46/0xb0
[  164.616568]
               -> #0 (&esw->offloads.encap_tbl_lock){+.+.}-{3:3}:
[  164.617210]        __lock_acquire+0x159e/0x26e0
[  164.617638]        lock_acquire+0xc2/0x2a0
[  164.618018]        __mutex_lock+0x92/0xcd0
[  164.618401]        mlx5e_attach_encap+0xd8/0x8b0 [mlx5_core]
[  164.618943]        post_process_attr+0x153/0x2d0 [mlx5_core]
[  164.619471]        mlx5e_tc_add_fdb_flow+0x164/0x360 [mlx5_core]
[  164.620021]        __mlx5e_add_fdb_flow+0x2d2/0x430 [mlx5_core]
[  164.620564]        mlx5e_configure_flower+0xe33/0x1a20 [mlx5_core]
[  164.621125]        tc_setup_cb_add+0xd4/0x200
[  164.621531]        fl_hw_replace_filter+0x14c/0x1f0 [cls_flower]
[  164.622047]        fl_change+0xc95/0x18a0 [cls_flower]
[  164.622500]        tc_new_tfilter+0x3fc/0xd20
[  164.622906]        rtnetlink_rcv_msg+0x418/0x5b0
[  164.623324]        netlink_rcv_skb+0x54/0x100
[  164.623727]        netlink_unicast+0x190/0x250
[  164.624138]        netlink_sendmsg+0x245/0x4a0
[  164.624544]        sock_sendmsg+0x38/0x60
[  164.624919]        ____sys_sendmsg+0x1d0/0x1e0
[  164.625340]        ___sys_sendmsg+0x80/0xc0
[  164.625731]        __sys_sendmsg+0x51/0x90
[  164.626117]        do_syscall_64+0x3d/0x90
[  164.626502]        entry_SYSCALL_64_after_hwframe+0x46/0xb0
[  164.626995]
               other info that might help us debug this:

[  164.627725]  Possible unsafe locking scenario:

[  164.628268]        CPU0                    CPU1
[  164.628683]        ----                    ----
[  164.629098]   lock(&comp->sem);
[  164.629421]                                lock(&esw->offloads.encap_tbl_lock);
[  164.630066]                                lock(&comp->sem);
[  164.630555]   lock(&esw->offloads.encap_tbl_lock);
[  164.630993]
                *** DEADLOCK ***

[  164.631575] 3 locks held by handler1/3456:
[  164.631962]  #0: ffff888124b75130 (&block->cb_lock){++++}-{3:3}, at: tc_setup_cb_add+0x5b/0x200
[  164.632703]  #1: ffff888116e512b8 (&esw->mode_lock){++++}-{3:3}, at: mlx5_esw_hold+0x39/0x50 [mlx5_core]
[  164.633552]  #2: ffff88810137fc98 (&comp->sem){++++}-{3:3}, at: mlx5_devcom_get_peer_data+0x37/0x80 [mlx5_core]
[  164.634435]
               stack backtrace:
[  164.634883] CPU: 17 PID: 3456 Comm: handler1 Not tainted 6.3.0-rc3+ #1
[  164.635431] Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS rel-1.13.0-0-gf21b5a4aeb02-prebuilt.qemu.org 04/01/2014
[  164.636340] Call Trace:
[  164.636616]  <TASK>
[  164.636863]  dump_stack_lvl+0x47/0x70
[  164.637217]  check_noncircular+0xfe/0x110
[  164.637601]  __lock_acquire+0x159e/0x26e0
[  164.637977]  ? mlx5_cmd_set_fte+0x5b0/0x830 [mlx5_core]
[  164.638472]  lock_acquire+0xc2/0x2a0
[  164.638828]  ? mlx5e_attach_encap+0xd8/0x8b0 [mlx5_core]
[  164.639339]  ? lock_is_held_type+0x98/0x110
[  164.639728]  __mutex_lock+0x92/0xcd0
[  164.640074]  ? mlx5e_attach_encap+0xd8/0x8b0 [mlx5_core]
[  164.640576]  ? __lock_acquire+0x382/0x26e0
[  164.640958]  ? mlx5e_attach_encap+0xd8/0x8b0 [mlx5_core]
[  164.641468]  ? mlx5e_attach_encap+0xd8/0x8b0 [mlx5_core]
[  164.641965]  mlx5e_attach_encap+0xd8/0x8b0 [mlx5_core]
[  164.642454]  ? lock_release+0xbf/0x240
[  164.642819]  post_process_attr+0x153/0x2d0 [mlx5_core]
[  164.643318]  mlx5e_tc_add_fdb_flow+0x164/0x360 [mlx5_core]
[  164.643835]  __mlx5e_add_fdb_flow+0x2d2/0x430 [mlx5_core]
[  164.644340]  mlx5e_configure_flower+0xe33/0x1a20 [mlx5_core]
[  164.644862]  ? lock_acquire+0xc2/0x2a0
[  164.645219]  tc_setup_cb_add+0xd4/0x200
[  164.645588]  fl_hw_replace_filter+0x14c/0x1f0 [cls_flower]
[  164.646067]  fl_change+0xc95/0x18a0 [cls_flower]
[  164.646488]  tc_new_tfilter+0x3fc/0xd20
[  164.646861]  ? tc_del_tfilter+0x810/0x810
[  164.647236]  rtnetlink_rcv_msg+0x418/0x5b0
[  164.647621]  ? rtnl_setlink+0x160/0x160
[  164.647982]  netlink_rcv_skb+0x54/0x100
[  164.648348]  netlink_unicast+0x190/0x250
[  164.648722]  netlink_sendmsg+0x245/0x4a0
[  164.649090]  sock_sendmsg+0x38/0x60
[  164.649434]  ____sys_sendmsg+0x1d0/0x1e0
[  164.649804]  ? copy_msghdr_from_user+0x6d/0xa0
[  164.650213]  ___sys_sendmsg+0x80/0xc0
[  164.650563]  ? lock_acquire+0xc2/0x2a0
[  164.650926]  ? lock_acquire+0xc2/0x2a0
[  164.651286]  ? __fget_files+0x5/0x190
[  164.651644]  ? find_held_lock+0x2b/0x80
[  164.652006]  ? __fget_files+0xb9/0x190
[  164.652365]  ? lock_release+0xbf/0x240
[  164.652723]  ? __fget_files+0xd3/0x190
[  164.653079]  __sys_sendmsg+0x51/0x90
[  164.653435]  do_syscall_64+0x3d/0x90
[  164.653784]  entry_SYSCALL_64_after_hwframe+0x46/0xb0
[  164.654229] RIP: 0033:0x7f378054f8bd
[  164.654577] Code: 28 89 54 24 1c 48 89 74 24 10 89 7c 24 08 e8 6a c3 f4 ff 8b 54 24 1c 48 8b 74 24 10 41 89 c0 8b 7c 24 08 b8 2e 00 00 00 0f 05 <48> 3d 00 f0 ff ff 77 33 44 89 c7 48 89 44 24 08 e8 be c3 f4 ff 48
[  164.656041] RSP: 002b:00007f377fa114b0 EFLAGS: 00000293 ORIG_RAX: 000000000000002e
[  164.656701] RAX: ffffffffffffffda RBX: 0000000000000001 RCX: 00007f378054f8bd
[  164.657297] RDX: 0000000000000000 RSI: 00007f377fa11540 RDI: 0000000000000014
[  164.657885] RBP: 00007f377fa12278 R08: 0000000000000000 R09: 000000000000015c
[  164.658472] R10: 00007f377fa123d0 R11: 0000000000000293 R12: 0000560962d99bd0
[  164.665317] R13: 0000000000000000 R14: 0000560962d99bd0 R15: 00007f377fa11540

Fixes: f9d196bd632b ("net/mlx5e: Use correct eswitch for stack devices with lag")
Signed-off-by: Vlad Buslov <[email-masked]>
Reviewed-by: Roi Dayan <[email-masked]>
Reviewed-by: Shay Drory <[email-masked]>
Reviewed-by: Tariq Toukan <[email-masked]>
Signed-off-by: Saeed Mahameed <[email-masked]>
---
 .../net/ethernet/mellanox/mlx5/core/en_tc.c   | 19 ++++----
 .../ethernet/mellanox/mlx5/core/lib/devcom.c  | 48 ++++++++++++++-----
 .../ethernet/mellanox/mlx5/core/lib/devcom.h  |  1 +
 3 files changed, 48 insertions(+), 20 deletions(-)

diff --git a/drivers/net/ethernet/mellanox/mlx5/core/en_tc.c b/drivers/net/ethernet/mellanox/mlx5/core/en_tc.c
index 65fe40f55d84..416ab6b6da97 100644
--- a/drivers/net/ethernet/mellanox/mlx5/core/en_tc.c
+++ b/drivers/net/ethernet/mellanox/mlx5/core/en_tc.c
@@ -1665,11 +1665,9 @@ bool mlx5e_tc_is_vf_tunnel(struct net_device *out_dev, struct net_device *route_
 int mlx5e_tc_query_route_vport(struct net_device *out_dev, struct net_device *route_dev, u16 *vport)
 {
 	struct mlx5e_priv *out_priv, *route_priv;
-	struct mlx5_devcom *devcom = NULL;
 	struct mlx5_core_dev *route_mdev;
 	struct mlx5_eswitch *esw;
 	u16 vhca_id;
-	int err;
 
 	out_priv = netdev_priv(out_dev);
 	esw = out_priv->mdev->priv.eswitch;
@@ -1678,6 +1676,9 @@ int mlx5e_tc_query_route_vport(struct net_device *out_dev, struct net_device *ro
 
 	vhca_id = MLX5_CAP_GEN(route_mdev, vhca_id);
 	if (mlx5_lag_is_active(out_priv->mdev)) {
+		struct mlx5_devcom *devcom;
+		int err;
+
 		/* In lag case we may get devices from different eswitch instances.
 		 * If we failed to get vport num, it means, mostly, that we on the wrong
 		 * eswitch.
@@ -1686,16 +1687,16 @@ int mlx5e_tc_query_route_vport(struct net_device *out_dev, struct net_device *ro
 		if (err != -ENOENT)
 			return err;
 
+		rcu_read_lock();
 		devcom = out_priv->mdev->priv.devcom;
-		esw = mlx5_devcom_get_peer_data(devcom, MLX5_DEVCOM_ESW_OFFLOADS);
-		if (!esw)
-			return -ENODEV;
+		esw = mlx5_devcom_get_peer_data_rcu(devcom, MLX5_DEVCOM_ESW_OFFLOADS);
+		err = esw ? mlx5_eswitch_vhca_id_to_vport(esw, vhca_id, vport) : -ENODEV;
+		rcu_read_unlock();
+
+		return err;
 	}
 
-	err = mlx5_eswitch_vhca_id_to_vport(esw, vhca_id, vport);
-	if (devcom)
-		mlx5_devcom_release_peer_data(devcom, MLX5_DEVCOM_ESW_OFFLOADS);
-	return err;
+	return mlx5_eswitch_vhca_id_to_vport(esw, vhca_id, vport);
 }
 
 static int
diff --git a/drivers/net/ethernet/mellanox/mlx5/core/lib/devcom.c b/drivers/net/ethernet/mellanox/mlx5/core/lib/devcom.c
index adefde3ea941..070d55f13419 100644
--- a/drivers/net/ethernet/mellanox/mlx5/core/lib/devcom.c
+++ b/drivers/net/ethernet/mellanox/mlx5/core/lib/devcom.c
@@ -13,7 +13,7 @@ static LIST_HEAD(devcom_list);
 
 struct mlx5_devcom_component {
 	struct {
-		void *data;
+		void __rcu *data;
 	} device[MLX5_DEVCOM_PORTS_SUPPORTED];
 
 	mlx5_devcom_event_handler_t handler;
@@ -162,7 +162,7 @@ void mlx5_devcom_register_component(struct mlx5_devcom *devcom,
 	comp = &devcom->priv->components[id];
 	down_write(&comp->sem);
 	comp->handler = handler;
-	comp->device[devcom->idx].data = data;
+	rcu_assign_pointer(comp->device[devcom->idx].data, data);
 	up_write(&comp->sem);
 }
 
@@ -176,8 +176,9 @@ void mlx5_devcom_unregister_component(struct mlx5_devcom *devcom,
 
 	comp = &devcom->priv->components[id];
 	down_write(&comp->sem);
-	comp->device[devcom->idx].data = NULL;
+	RCU_INIT_POINTER(comp->device[devcom->idx].data, NULL);
 	up_write(&comp->sem);
+	synchronize_rcu();
 }
 
 int mlx5_devcom_send_event(struct mlx5_devcom *devcom,
@@ -193,12 +194,15 @@ int mlx5_devcom_send_event(struct mlx5_devcom *devcom,
 
 	comp = &devcom->priv->components[id];
 	down_write(&comp->sem);
-	for (i = 0; i < MLX5_DEVCOM_PORTS_SUPPORTED; i++)
-		if (i != devcom->idx && comp->device[i].data) {
-			err = comp->handler(event, comp->device[i].data,
-					    event_data);
+	for (i = 0; i < MLX5_DEVCOM_PORTS_SUPPORTED; i++) {
+		void *data = rcu_dereference_protected(comp->device[i].data,
+						       lockdep_is_held(&comp->sem));
+
+		if (i != devcom->idx && data) {
+			err = comp->handler(event, data, event_data);
 			break;
 		}
+	}
 
 	up_write(&comp->sem);
 	return err;
@@ -213,7 +217,7 @@ void mlx5_devcom_set_paired(struct mlx5_devcom *devcom,
 	comp = &devcom->priv->components[id];
 	WARN_ON(!rwsem_is_locked(&comp->sem));
 
-	comp->paired = paired;
+	WRITE_ONCE(comp->paired, paired);
 }
 
 bool mlx5_devcom_is_paired(struct mlx5_devcom *devcom,
@@ -222,7 +226,7 @@ bool mlx5_devcom_is_paired(struct mlx5_devcom *devcom,
 	if (IS_ERR_OR_NULL(devcom))
 		return false;
 
-	return devcom->priv->components[id].paired;
+	return READ_ONCE(devcom->priv->components[id].paired);
 }
 
 void *mlx5_devcom_get_peer_data(struct mlx5_devcom *devcom,
@@ -236,7 +240,7 @@ void *mlx5_devcom_get_peer_data(struct mlx5_devcom *devcom,
 
 	comp = &devcom->priv->components[id];
 	down_read(&comp->sem);
-	if (!comp->paired) {
+	if (!READ_ONCE(comp->paired)) {
 		up_read(&comp->sem);
 		return NULL;
 	}
@@ -245,7 +249,29 @@ void *mlx5_devcom_get_peer_data(struct mlx5_devcom *devcom,
 		if (i != devcom->idx)
 			break;
 
-	return comp->device[i].data;
+	return rcu_dereference_protected(comp->device[i].data, lockdep_is_held(&comp->sem));
+}
+
+void *mlx5_devcom_get_peer_data_rcu(struct mlx5_devcom *devcom, enum mlx5_devcom_components id)
+{
+	struct mlx5_devcom_component *comp;
+	int i;
+
+	if (IS_ERR_OR_NULL(devcom))
+		return NULL;
+
+	for (i = 0; i < MLX5_DEVCOM_PORTS_SUPPORTED; i++)
+		if (i != devcom->idx)
+			break;
+
+	comp = &devcom->priv->components[id];
+	/* This can change concurrently, however 'data' pointer will remain
+	 * valid for the duration of RCU read section.
+	 */
+	if (!READ_ONCE(comp->paired))
+		return NULL;
+
+	return rcu_dereference(comp->device[i].data);
 }
 
 void mlx5_devcom_release_peer_data(struct mlx5_devcom *devcom,
diff --git a/drivers/net/ethernet/mellanox/mlx5/core/lib/devcom.h b/drivers/net/ethernet/mellanox/mlx5/core/lib/devcom.h
index 94313c18bb64..9a496f4722da 100644
--- a/drivers/net/ethernet/mellanox/mlx5/core/lib/devcom.h
+++ b/drivers/net/ethernet/mellanox/mlx5/core/lib/devcom.h
@@ -41,6 +41,7 @@ bool mlx5_devcom_is_paired(struct mlx5_devcom *devcom,
 
 void *mlx5_devcom_get_peer_data(struct mlx5_devcom *devcom,
 				enum mlx5_devcom_components id);
+void *mlx5_devcom_get_peer_data_rcu(struct mlx5_devcom *devcom, enum mlx5_devcom_components id);
 void mlx5_devcom_release_peer_data(struct mlx5_devcom *devcom,
 				   enum mlx5_devcom_components id);
 
-- 
2.40.1