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Commit a7e1f049 authored by Jack Morgenstein's avatar Jack Morgenstein Committed by David S. Miller
Browse files

net/mlx4_core: Fix deadlock when switching between polling and event fw commands 



When switching from polling-based fw commands to event-based fw
commands, there is a race condition which could cause a fw command
in another task to hang: that task will keep waiting for the polling
sempahore, but may never be able to acquire it. This is due to
mlx4_cmd_use_events, which "down"s the sempahore back to 0.

During driver initialization, this is not a problem, since no other
tasks which invoke FW commands are active.

However, there is a problem if the driver switches to polling mode
and then back to event mode during normal operation.

The "test_interrupts" feature does exactly that.
Running "ethtool -t <eth device> offline" causes the PF driver to
temporarily switch to polling mode, and then back to event mode.
(Note that for VF drivers, such switching is not performed).

Fix this by adding a read-write semaphore for protection when
switching between modes.

Fixes: 225c7b1f ("IB/mlx4: Add a driver Mellanox ConnectX InfiniBand adapters")
Signed-off-by: default avatarJack Morgenstein <jackm@dev.mellanox.co.il>
Signed-off-by: default avatarMatan Barak <matanb@mellanox.com>
Signed-off-by: default avatarTariq Toukan <tariqt@mellanox.com>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent 30353bfc

drivers/net/ethernet/mellanox/mlx4/cmd.c

+17 −6
Original line number Diff line number Diff line
@@ -785,17 +785,23 @@ int __mlx4_cmd(struct mlx4_dev *dev, u64 in_param, u64 *out_param, 
		return mlx4_cmd_reset_flow(dev, op, op_modifier, -EIO);



	if (!mlx4_is_mfunc(dev) || (native && mlx4_is_master(dev))) {

		int ret;



		if (dev->persist->state & MLX4_DEVICE_STATE_INTERNAL_ERROR)

			return mlx4_internal_err_ret_value(dev, op,

							  op_modifier);

		down_read(&mlx4_priv(dev)->cmd.switch_sem);

		if (mlx4_priv(dev)->cmd.use_events)

			return mlx4_cmd_wait(dev, in_param, out_param,

			ret = mlx4_cmd_wait(dev, in_param, out_param,

					    out_is_imm, in_modifier,

					    op_modifier, op, timeout);

		else

			return mlx4_cmd_poll(dev, in_param, out_param,

			ret = mlx4_cmd_poll(dev, in_param, out_param,

					    out_is_imm, in_modifier,

					    op_modifier, op, timeout);



		up_read(&mlx4_priv(dev)->cmd.switch_sem);

		return ret;

	}

	return mlx4_slave_cmd(dev, in_param, out_param, out_is_imm,

			      in_modifier, op_modifier, op, timeout);
@@ -2454,6 +2460,7 @@ int mlx4_cmd_init(struct mlx4_dev *dev) 
	int flags = 0;



	if (!priv->cmd.initialized) {

		init_rwsem(&priv->cmd.switch_sem);

		mutex_init(&priv->cmd.slave_cmd_mutex);

		sema_init(&priv->cmd.poll_sem, 1);

		priv->cmd.use_events = 0;
@@ -2583,6 +2590,7 @@ int mlx4_cmd_use_events(struct mlx4_dev *dev) 
	if (!priv->cmd.context)

		return -ENOMEM;



	down_write(&priv->cmd.switch_sem);

	for (i = 0; i < priv->cmd.max_cmds; ++i) {

		priv->cmd.context[i].token = i;

		priv->cmd.context[i].next  = i + 1;
@@ -2606,6 +2614,7 @@ int mlx4_cmd_use_events(struct mlx4_dev *dev) 


	down(&priv->cmd.poll_sem);

	priv->cmd.use_events = 1;

	up_write(&priv->cmd.switch_sem);



	return err;

}
@@ -2618,6 +2627,7 @@ void mlx4_cmd_use_polling(struct mlx4_dev *dev) 
	struct mlx4_priv *priv = mlx4_priv(dev);

	int i;



	down_write(&priv->cmd.switch_sem);

	priv->cmd.use_events = 0;



	for (i = 0; i < priv->cmd.max_cmds; ++i)
@@ -2626,6 +2636,7 @@ void mlx4_cmd_use_polling(struct mlx4_dev *dev) 
	kfree(priv->cmd.context);



	up(&priv->cmd.poll_sem);

	up_write(&priv->cmd.switch_sem);

}



struct mlx4_cmd_mailbox *mlx4_alloc_cmd_mailbox(struct mlx4_dev *dev)

drivers/net/ethernet/mellanox/mlx4/mlx4.h

+2 −0
Original line number Diff line number Diff line
@@ -46,6 +46,7 @@ 
#include <linux/interrupt.h>

#include <linux/spinlock.h>

#include <net/devlink.h>

#include <linux/rwsem.h>



#include <linux/mlx4/device.h>

#include <linux/mlx4/driver.h>
@@ -627,6 +628,7 @@ struct mlx4_cmd { 
	struct mutex		slave_cmd_mutex;

	struct semaphore	poll_sem;

	struct semaphore	event_sem;

	struct rw_semaphore	switch_sem;

	int			max_cmds;

	spinlock_t		context_lock;

	int			free_head;