On Wed, 28 Oct 2015 03:45:50 +0100
Arnd Bergmann <a...@arndb.de> wrote:
> As far as I can tell, there is a preexisting race condition
> regarding the cmd->use_events flag, which is not protected
> by any lock. When this flag is toggled while another command
> is being started, that command gets stuck until the mode is
> toggled back.
We fixed this issue in mellanox ofed in a manner that allowed keeping
the same counting mechanism. IMHO, this is preferable, rather than
totally changing the mechanism.
We will submit a similar patch to the upstream kernel shortly.
-Jack
net/mlx4: Switching between sending commands via polling and events may results
in hung tasks
When switching between those methonds of sending commands, it's possbile that a
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.
Reproducing it involves in sending commands while chaning between
mlx4_cmd_use_polling
and mlx4_cmd_use_events.
Solving it by adding a read-write semaphore when switching between modes.
issue: 402565
Change-Id: I19f0d40dbb327c49b39a9abbcb2bb002b0279b0b
Signed-off-by: Matan Barak <mat...@mellanox.com>
---
drivers/net/ethernet/mellanox/mlx4/cmd.c | 23 +++++++++++++++++------
drivers/net/ethernet/mellanox/mlx4/mlx4.h | 2 ++
2 files changed, 19 insertions(+), 6 deletions(-)
diff --git a/drivers/net/ethernet/mellanox/mlx4/cmd.c
b/drivers/net/ethernet/mellanox/mlx4/cmd.c
index def1338..f94a960 100644
--- a/drivers/net/ethernet/mellanox/mlx4/cmd.c
+++ b/drivers/net/ethernet/mellanox/mlx4/cmd.c
@@ -766,17 +766,23 @@ 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,
- 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;
}
return mlx4_slave_cmd(dev, in_param, out_param, out_is_imm,
in_modifier, op_modifier, op, timeout);
@@ -2437,6 +2443,7 @@ 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;
@@ -2566,6 +2573,7 @@ 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;
@@ -2590,6 +2598,7 @@ 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;
}
@@ -2602,6 +2611,7 @@ 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)
@@ -2610,6 +2620,7 @@ 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)
diff --git a/drivers/net/ethernet/mellanox/mlx4/mlx4.h
b/drivers/net/ethernet/mellanox/mlx4/mlx4.h
index 6c58021..2f03e6e 100644
--- a/drivers/net/ethernet/mellanox/mlx4/mlx4.h
+++ b/drivers/net/ethernet/mellanox/mlx4/mlx4.h
@@ -45,6 +45,7 @@
#include <linux/workqueue.h>
#include <linux/interrupt.h>
#include <linux/spinlock.h>
+#include <linux/rwsem.h>
#include <linux/mlx4/device.h>
#include <linux/mlx4/driver.h>
@@ -626,6 +627,7 @@ 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;
--
1.8.1.2
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