[PATCH 3.2 026/126] net/mlx4_core: Fix deadlock when switching between polling and event fw commands

Ben Hutchings
2017-02-15T23:08:12Z

From: Jack Morgenstein <jackm@dev.mellanox.co.il>

commit a7e1f04905e5b2b90251974dddde781301b6be37 upstream.

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: 225c7b1feef1 ("IB/mlx4: Add a driver Mellanox ConnectX InfiniBand adapters")
Signed-off-by: Jack Morgenstein <jackm@dev.mellanox.co.il>
Signed-off-by: Matan Barak <matanb@mellanox.com>
Signed-off-by: Tariq Toukan <tariqt@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
[bwh: Backported to 3.2: adjust context, indentation]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
---
--- a/drivers/net/ethernet/mellanox/mlx4/cmd.c
+++ b/drivers/net/ethernet/mellanox/mlx4/cmd.c
@@ -313,12 +313,18 @@ int __mlx4_cmd(struct mlx4_dev *dev, u64
int out_is_imm, u32 in_modifier, u8 op_modifier,
u16 op, unsigned long timeout)
{
+ int ret;
+
+ down_read(&mlx4_priv(dev)->cmd.switch_sem);
if (mlx4_priv(dev)->cmd.use_events)
- return mlx4_cmd_wait(dev, in_param, out_param, out_is_imm,
- in_modifier, op_modifier, op, timeout);
+ 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, out_is_imm,
- in_modifier, op_modifier, op, timeout);
+ 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;
}
EXPORT_SYMBOL_GPL(__mlx4_cmd);

@@ -326,6 +332,7 @@ int mlx4_cmd_init(struct mlx4_dev *dev)
{
struct mlx4_priv *priv = mlx4_priv(dev);

+ init_rwsem(&priv->cmd.switch_sem);
mutex_init(&priv->cmd.hcr_mutex);
sema_init(&priv->cmd.poll_sem, 1);
priv->cmd.use_events = 0;
@@ -372,6 +379,7 @@ int mlx4_cmd_use_events(struct mlx4_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;
@@ -390,6 +398,7 @@ int mlx4_cmd_use_events(struct mlx4_dev
--priv->cmd.token_mask;

priv->cmd.use_events = 1;
+ up_write(&priv->cmd.switch_sem);

down(&priv->cmd.poll_sem);

@@ -404,6 +413,7 @@ void mlx4_cmd_use_polling(struct mlx4_de
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)
@@ -412,6 +422,7 @@ void mlx4_cmd_use_polling(struct mlx4_de
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)
--- a/drivers/net/ethernet/mellanox/mlx4/mlx4.h
+++ b/drivers/net/ethernet/mellanox/mlx4/mlx4.h
@@ -42,6 +42,7 @@
#include <linux/timer.h>
#include <linux/semaphore.h>
#include <linux/workqueue.h>
+#include <linux/rwsem.h>

#include <linux/mlx4/device.h>
#include <linux/mlx4/driver.h>
@@ -190,6 +191,7 @@ struct mlx4_cmd {
struct mutex hcr_mutex;
struct semaphore poll_sem;
struct semaphore event_sem;
+ struct rw_semaphore switch_sem;
int max_cmds;
spinlock_t context_lock;
int free_head;