Subject: Re: [PATCH net V5 3/3] bonding: change ipsec_lock from spin lock to mutex

From: Jay Vosburgh <[email-masked]>
Date: Wed, 21 Aug 2024 09:00:30 -0700

Jianbo Liu <[email-masked]> wrote:

>In the cited commit, bond->ipsec_lock is added to protect ipsec_list,
>hence xdo_dev_state_add and xdo_dev_state_delete are called inside
>this lock. As ipsec_lock is a spin lock and such xfrmdev ops may sleep,
>"scheduling while atomic" will be triggered when changing bond's
>active slave.
>
>[  101.055189] BUG: scheduling while atomic: bash/902/0x00000200
>[  101.055726] Modules linked in:
>[  101.058211] CPU: 3 PID: 902 Comm: bash Not tainted 6.9.0-rc4+ #1
>[  101.058760] Hardware name:
>[  101.059434] Call Trace:
>[  101.059436]  <TASK>
>[  101.060873]  dump_stack_lvl+0x51/0x60
>[  101.061275]  __schedule_bug+0x4e/0x60
>[  101.061682]  __schedule+0x612/0x7c0
>[  101.062078]  ? __mod_timer+0x25c/0x370
>[  101.062486]  schedule+0x25/0xd0
>[  101.062845]  schedule_timeout+0x77/0xf0
>[  101.063265]  ? asm_common_interrupt+0x22/0x40
>[  101.063724]  ? __bpf_trace_itimer_state+0x10/0x10
>[  101.064215]  __wait_for_common+0x87/0x190
>[  101.064648]  ? usleep_range_state+0x90/0x90
>[  101.065091]  cmd_exec+0x437/0xb20 [mlx5_core]
>[  101.065569]  mlx5_cmd_do+0x1e/0x40 [mlx5_core]
>[  101.066051]  mlx5_cmd_exec+0x18/0x30 [mlx5_core]
>[  101.066552]  mlx5_crypto_create_dek_key+0xea/0x120 [mlx5_core]
>[  101.067163]  ? bonding_sysfs_store_option+0x4d/0x80 [bonding]
>[  101.067738]  ? kmalloc_trace+0x4d/0x350
>[  101.068156]  mlx5_ipsec_create_sa_ctx+0x33/0x100 [mlx5_core]
>[  101.068747]  mlx5e_xfrm_add_state+0x47b/0xaa0 [mlx5_core]
>[  101.069312]  bond_change_active_slave+0x392/0x900 [bonding]
>[  101.069868]  bond_option_active_slave_set+0x1c2/0x240 [bonding]
>[  101.070454]  __bond_opt_set+0xa6/0x430 [bonding]
>[  101.070935]  __bond_opt_set_notify+0x2f/0x90 [bonding]
>[  101.071453]  bond_opt_tryset_rtnl+0x72/0xb0 [bonding]
>[  101.071965]  bonding_sysfs_store_option+0x4d/0x80 [bonding]
>[  101.072567]  kernfs_fop_write_iter+0x10c/0x1a0
>[  101.073033]  vfs_write+0x2d8/0x400
>[  101.073416]  ? alloc_fd+0x48/0x180
>[  101.073798]  ksys_write+0x5f/0xe0
>[  101.074175]  do_syscall_64+0x52/0x110
>[  101.074576]  entry_SYSCALL_64_after_hwframe+0x4b/0x53
>
>As bond_ipsec_add_sa_all and bond_ipsec_del_sa_all are only called
>from bond_change_active_slave, which requires holding the RTNL lock.
>And bond_ipsec_add_sa and bond_ipsec_del_sa are xfrm state
>xdo_dev_state_add and xdo_dev_state_delete APIs, which are in user
>context. So ipsec_lock doesn't have to be spin lock, change it to
>mutex, and thus the above issue can be resolved.
>
>Fixes: 9a5605505d9c ("bonding: Add struct bond_ipesc to manage SA")
>Signed-off-by: Jianbo Liu <[email-masked]>
>Signed-off-by: Tariq Toukan <[email-masked]>
>Reviewed-by: Hangbin Liu <[email-masked]>
>---
> drivers/net/bonding/bond_main.c | 67 +++++++++++++++------------------
> include/net/bonding.h           |  2 +-
> 2 files changed, 32 insertions(+), 37 deletions(-)
>
>diff --git a/drivers/net/bonding/bond_main.c b/drivers/net/bonding/bond_main.c
>index 0d1129eaf47b..f20f6d83ad54 100644
>--- a/drivers/net/bonding/bond_main.c
>+++ b/drivers/net/bonding/bond_main.c
>@@ -439,38 +439,33 @@ static int bond_ipsec_add_sa(struct xfrm_state *xs,
> 	rcu_read_lock();
> 	bond = netdev_priv(bond_dev);
> 	slave = rcu_dereference(bond->curr_active_slave);
>-	if (!slave) {
>-		rcu_read_unlock();
>+	real_dev = slave ? slave->dev : NULL;
>+	rcu_read_unlock();
>+	if (!real_dev)
> 		return -ENODEV;

	In reading these, I was confused as to why some changes use
rcu_read_lock(), rcu_dereference() and others use rtnl_dereference(); I
think it's because bond_ipsec_{add,del}_sa_all() are guaranteed to be
called under RTNL, while the bond_ipsec_{add,del}_sa() functions are do
not have that guarantee.  Am I understanding correctly?

>-	}
> 
>-	real_dev = slave->dev;
> 	if (!real_dev->xfrmdev_ops ||
> 	    !real_dev->xfrmdev_ops->xdo_dev_state_add ||
> 	    netif_is_bond_master(real_dev)) {
> 		NL_SET_ERR_MSG_MOD(extack, "Slave does not support ipsec offload");
>-		rcu_read_unlock();
> 		return -EINVAL;
> 	}
> 
>-	ipsec = kmalloc(sizeof(*ipsec), GFP_ATOMIC);
>-	if (!ipsec) {
>-		rcu_read_unlock();
>+	ipsec = kmalloc(sizeof(*ipsec), GFP_KERNEL);
>+	if (!ipsec)
> 		return -ENOMEM;

	Presumably the switch from ATOMIC to KERNEL is safe because this
is only called under RTNL (and therefore always has a process context),
i.e., this change is independent of any other changes in the patch.
Correct?

>-	}
> 
> 	xs->xso.real_dev = real_dev;
> 	err = real_dev->xfrmdev_ops->xdo_dev_state_add(xs, extack);
> 	if (!err) {
> 		ipsec->xs = xs;
> 		INIT_LIST_HEAD(&ipsec->list);
>-		spin_lock_bh(&bond->ipsec_lock);
>+		mutex_lock(&bond->ipsec_lock);
> 		list_add(&ipsec->list, &bond->ipsec_list);
>-		spin_unlock_bh(&bond->ipsec_lock);
>+		mutex_unlock(&bond->ipsec_lock);
> 	} else {
> 		kfree(ipsec);
> 	}
>-	rcu_read_unlock();
> 	return err;
> }
> 
>@@ -481,35 +476,35 @@ static void bond_ipsec_add_sa_all(struct bonding *bond)
> 	struct bond_ipsec *ipsec;
> 	struct slave *slave;
> 
>-	rcu_read_lock();
>-	slave = rcu_dereference(bond->curr_active_slave);
>-	if (!slave)
>-		goto out;
>+	slave = rtnl_dereference(bond->curr_active_slave);
>+	real_dev = slave ? slave->dev : NULL;
>+	if (!real_dev)
>+		return;
> 
>-	real_dev = slave->dev;
>+	mutex_lock(&bond->ipsec_lock);
> 	if (!real_dev->xfrmdev_ops ||
> 	    !real_dev->xfrmdev_ops->xdo_dev_state_add ||
> 	    netif_is_bond_master(real_dev)) {
>-		spin_lock_bh(&bond->ipsec_lock);
> 		if (!list_empty(&bond->ipsec_list))
> 			slave_warn(bond_dev, real_dev,
> 				   "%s: no slave xdo_dev_state_add\n",
> 				   __func__);
>-		spin_unlock_bh(&bond->ipsec_lock);
> 		goto out;
> 	}
> 
>-	spin_lock_bh(&bond->ipsec_lock);
> 	list_for_each_entry(ipsec, &bond->ipsec_list, list) {
>+		/* If new state is added before ipsec_lock acquired */
>+		if (ipsec->xs->xso.real_dev == real_dev)
>+			continue;
>+
> 		ipsec->xs->xso.real_dev = real_dev;
> 		if (real_dev->xfrmdev_ops->xdo_dev_state_add(ipsec->xs, NULL)) {
> 			slave_warn(bond_dev, real_dev, "%s: failed to add SA\n", __func__);
> 			ipsec->xs->xso.real_dev = NULL;
> 		}
> 	}
>-	spin_unlock_bh(&bond->ipsec_lock);
> out:
>-	rcu_read_unlock();
>+	mutex_unlock(&bond->ipsec_lock);
> }
> 
> /**
>@@ -530,6 +525,8 @@ static void bond_ipsec_del_sa(struct xfrm_state *xs)
> 	rcu_read_lock();
> 	bond = netdev_priv(bond_dev);
> 	slave = rcu_dereference(bond->curr_active_slave);
>+	real_dev = slave ? slave->dev : NULL;
>+	rcu_read_unlock();

	Is it really safe to access real_dev once we've left the rcu
critical section?  What prevents the device referenced by real_dev from
being deleted as soon as rcu_read_unlock() completes?

	-J
	
> 
> 	if (!slave)
> 		goto out;
>@@ -537,7 +534,6 @@ static void bond_ipsec_del_sa(struct xfrm_state *xs)
> 	if (!xs->xso.real_dev)
> 		goto out;
> 
>-	real_dev = slave->dev;
> 	WARN_ON(xs->xso.real_dev != real_dev);
> 
> 	if (!real_dev->xfrmdev_ops ||
>@@ -549,7 +545,7 @@ static void bond_ipsec_del_sa(struct xfrm_state *xs)
> 
> 	real_dev->xfrmdev_ops->xdo_dev_state_delete(xs);
> out:
>-	spin_lock_bh(&bond->ipsec_lock);
>+	mutex_lock(&bond->ipsec_lock);
> 	list_for_each_entry(ipsec, &bond->ipsec_list, list) {
> 		if (ipsec->xs == xs) {
> 			list_del(&ipsec->list);
>@@ -557,8 +553,7 @@ static void bond_ipsec_del_sa(struct xfrm_state *xs)
> 			break;
> 		}
> 	}
>-	spin_unlock_bh(&bond->ipsec_lock);
>-	rcu_read_unlock();
>+	mutex_unlock(&bond->ipsec_lock);
> }
> 
> static void bond_ipsec_del_sa_all(struct bonding *bond)
>@@ -568,15 +563,12 @@ static void bond_ipsec_del_sa_all(struct bonding *bond)
> 	struct bond_ipsec *ipsec;
> 	struct slave *slave;
> 
>-	rcu_read_lock();
>-	slave = rcu_dereference(bond->curr_active_slave);
>-	if (!slave) {
>-		rcu_read_unlock();
>+	slave = rtnl_dereference(bond->curr_active_slave);
>+	real_dev = slave ? slave->dev : NULL;
>+	if (!real_dev)
> 		return;
>-	}
> 
>-	real_dev = slave->dev;
>-	spin_lock_bh(&bond->ipsec_lock);
>+	mutex_lock(&bond->ipsec_lock);
> 	list_for_each_entry(ipsec, &bond->ipsec_list, list) {
> 		if (!ipsec->xs->xso.real_dev)
> 			continue;
>@@ -593,8 +585,7 @@ static void bond_ipsec_del_sa_all(struct bonding *bond)
> 				real_dev->xfrmdev_ops->xdo_dev_state_free(ipsec->xs);
> 		}
> 	}
>-	spin_unlock_bh(&bond->ipsec_lock);
>-	rcu_read_unlock();
>+	mutex_unlock(&bond->ipsec_lock);
> }
> 
> static void bond_ipsec_free_sa(struct xfrm_state *xs)
>@@ -5917,7 +5908,7 @@ void bond_setup(struct net_device *bond_dev)
> 	/* set up xfrm device ops (only supported in active-backup right now) */
> 	bond_dev->xfrmdev_ops = &bond_xfrmdev_ops;
> 	INIT_LIST_HEAD(&bond->ipsec_list);
>-	spin_lock_init(&bond->ipsec_lock);
>+	mutex_init(&bond->ipsec_lock);
> #endif /* CONFIG_XFRM_OFFLOAD */
> 
> 	/* don't acquire bond device's netif_tx_lock when transmitting */
>@@ -5966,6 +5957,10 @@ static void bond_uninit(struct net_device *bond_dev)
> 		__bond_release_one(bond_dev, slave->dev, true, true);
> 	netdev_info(bond_dev, "Released all slaves\n");
> 
>+#ifdef CONFIG_XFRM_OFFLOAD
>+	mutex_destroy(&bond->ipsec_lock);
>+#endif /* CONFIG_XFRM_OFFLOAD */
>+
> 	bond_set_slave_arr(bond, NULL, NULL);
> 
> 	list_del_rcu(&bond->bond_list);
>diff --git a/include/net/bonding.h b/include/net/bonding.h
>index b61fb1aa3a56..8bb5f016969f 100644
>--- a/include/net/bonding.h
>+++ b/include/net/bonding.h
>@@ -260,7 +260,7 @@ struct bonding {
> #ifdef CONFIG_XFRM_OFFLOAD
> 	struct list_head ipsec_list;
> 	/* protecting ipsec_list */
>-	spinlock_t ipsec_lock;
>+	struct mutex ipsec_lock;
> #endif /* CONFIG_XFRM_OFFLOAD */
> 	struct bpf_prog *xdp_prog;
> };
>-- 
>2.21.0
>

---
	-Jay Vosburgh, [email-masked]