From: Vlad Buslov vladbu@nvidia.com
commit 691c041bf20899fc13c793f92ba61ab660fa3a30 upstream.
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 vladbu@nvidia.com Reviewed-by: Roi Dayan roid@nvidia.com Reviewed-by: Shay Drory shayd@nvidia.com Reviewed-by: Tariq Toukan tariqt@nvidia.com Signed-off-by: Saeed Mahameed saeedm@nvidia.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- drivers/net/ethernet/mellanox/mlx5/core/en_tc.c | 19 +++---- drivers/net/ethernet/mellanox/mlx5/core/lib/devcom.c | 48 ++++++++++++++----- drivers/net/ethernet/mellanox/mlx5/core/lib/devcom.h | 1 3 files changed, 48 insertions(+), 20 deletions(-)
--- a/drivers/net/ethernet/mellanox/mlx5/core/en_tc.c +++ b/drivers/net/ethernet/mellanox/mlx5/core/en_tc.c @@ -1578,11 +1578,9 @@ bool mlx5e_tc_is_vf_tunnel(struct net_de 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; @@ -1591,6 +1589,9 @@ int mlx5e_tc_query_route_vport(struct ne
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. @@ -1599,16 +1600,16 @@ int mlx5e_tc_query_route_vport(struct ne 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); }
int mlx5e_tc_add_flow_mod_hdr(struct mlx5e_priv *priv, --- 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(stru 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(st
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_d
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_ 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_d 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 m
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 m 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, --- 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_d
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);