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Date: Wed, 28 Oct 2015 03:45:50 +0100
From: Arnd Bergmann <arnd@...db.de>
To: tglx@...utronix.de
Cc: Arnd Bergmann <arnd@...db.de>,
Roland Dreier <roland@...estorage.com>,
Eli Cohen <eli@...lanox.co.il>,
Yevgeny Petrilin <yevgenyp@...lanox.co.il>,
netdev@...r.kernel.org, linux-rdma@...r.kernel.org
Subject: [PATCH 02/25] IB/mthca, net/mlx4: remove counting semaphores
The mthca and mlx4 device drivers use the same method
to switch between polling and event-driven command mode,
abusing two semaphores to create a mutual exclusion between
one polled command or multiple concurrent event driven
commands.
Since we want to make counting semaphores go away, this
patch replaces the semaphore counting the event-driven
commands with an open-coded wait-queue, which should
be an equivalent transformation of the code, although
it does not make it any nicer.
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.
A better solution that would solve the race condition and
at the same time improve the code readability would create
a new locking primitive that replaces both semaphores, like
static int mlx4_use_events(struct mlx4_cmd *cmd)
{
int ret = -EAGAIN;
spin_lock(&cmd->lock);
if (cmd->use_events && cmd->commands < cmd->max_commands) {
cmd->commands++;
ret = 1;
} else if (!cmd->use_events && cmd->commands == 0) {
cmd->commands = 1;
ret = 0;
}
spin_unlock(&cmd->lock);
return ret;
}
static bool mlx4_use_events(struct mlx4_cmd *cmd)
{
int ret;
wait_event(cmd->events_wq, ret = __mlx4_use_events(cmd) >= 0);
return ret;
}
Cc: Roland Dreier <roland@...estorage.com>
Cc: Eli Cohen <eli@...lanox.co.il>
Cc: Yevgeny Petrilin <yevgenyp@...lanox.co.il>
Cc: netdev@...r.kernel.org
Cc: linux-rdma@...r.kernel.org
Signed-off-by: Arnd Bergmann <arnd@...db.de>
Conflicts:
drivers/net/mlx4/cmd.c
drivers/net/mlx4/mlx4.h
---
drivers/infiniband/hw/mthca/mthca_cmd.c | 12 ++++++++----
drivers/infiniband/hw/mthca/mthca_dev.h | 3 ++-
drivers/net/ethernet/mellanox/mlx4/cmd.c | 12 ++++++++----
drivers/net/ethernet/mellanox/mlx4/mlx4.h | 3 ++-
4 files changed, 20 insertions(+), 10 deletions(-)
diff --git a/drivers/infiniband/hw/mthca/mthca_cmd.c b/drivers/infiniband/hw/mthca/mthca_cmd.c
index 9d3e5c1ac60e..aad1852e8e10 100644
--- a/drivers/infiniband/hw/mthca/mthca_cmd.c
+++ b/drivers/infiniband/hw/mthca/mthca_cmd.c
@@ -417,7 +417,8 @@ static int mthca_cmd_wait(struct mthca_dev *dev,
int err = 0;
struct mthca_cmd_context *context;
- down(&dev->cmd.event_sem);
+ wait_event(dev->cmd.event_wait,
+ atomic_add_unless(&dev->cmd.commands, -1, 0));
spin_lock(&dev->cmd.context_lock);
BUG_ON(dev->cmd.free_head < 0);
@@ -459,7 +460,8 @@ out:
dev->cmd.free_head = context - dev->cmd.context;
spin_unlock(&dev->cmd.context_lock);
- up(&dev->cmd.event_sem);
+ atomic_inc(&dev->cmd.commands);
+ wake_up(&dev->cmd.event_wait);
return err;
}
@@ -571,7 +573,8 @@ int mthca_cmd_use_events(struct mthca_dev *dev)
dev->cmd.context[dev->cmd.max_cmds - 1].next = -1;
dev->cmd.free_head = 0;
- sema_init(&dev->cmd.event_sem, dev->cmd.max_cmds);
+ init_waitqueue_head(&dev->cmd.event_wait);
+ atomic_set(&dev->cmd.commands, dev->cmd.max_cmds);
spin_lock_init(&dev->cmd.context_lock);
for (dev->cmd.token_mask = 1;
@@ -597,7 +600,8 @@ void mthca_cmd_use_polling(struct mthca_dev *dev)
dev->cmd.flags &= ~MTHCA_CMD_USE_EVENTS;
for (i = 0; i < dev->cmd.max_cmds; ++i)
- down(&dev->cmd.event_sem);
+ wait_event(dev->cmd.event_wait,
+ atomic_add_unless(&dev->cmd.commands, -1, 0));
kfree(dev->cmd.context);
diff --git a/drivers/infiniband/hw/mthca/mthca_dev.h b/drivers/infiniband/hw/mthca/mthca_dev.h
index 7e6a6d64ad4e..3055f5c12ac8 100644
--- a/drivers/infiniband/hw/mthca/mthca_dev.h
+++ b/drivers/infiniband/hw/mthca/mthca_dev.h
@@ -121,7 +121,8 @@ struct mthca_cmd {
struct pci_pool *pool;
struct mutex hcr_mutex;
struct semaphore poll_sem;
- struct semaphore event_sem;
+ wait_queue_head_t event_wait;
+ atomic_t commands;
int max_cmds;
spinlock_t context_lock;
int free_head;
diff --git a/drivers/net/ethernet/mellanox/mlx4/cmd.c b/drivers/net/ethernet/mellanox/mlx4/cmd.c
index 78f5a1a0b8c8..60134a4245ef 100644
--- a/drivers/net/ethernet/mellanox/mlx4/cmd.c
+++ b/drivers/net/ethernet/mellanox/mlx4/cmd.c
@@ -273,7 +273,8 @@ static int mlx4_cmd_wait(struct mlx4_dev *dev, u64 in_param, u64 *out_param,
struct mlx4_cmd_context *context;
int err = 0;
- down(&cmd->event_sem);
+ wait_event(cmd->event_wait,
+ atomic_add_unless(&cmd->commands, -1, 0));
spin_lock(&cmd->context_lock);
BUG_ON(cmd->free_head < 0);
@@ -305,7 +306,8 @@ out:
cmd->free_head = context - cmd->context;
spin_unlock(&cmd->context_lock);
- up(&cmd->event_sem);
+ atomic_inc(&cmd->commands);
+ wake_up(&cmd->event_wait);
return err;
}
@@ -380,7 +382,8 @@ int mlx4_cmd_use_events(struct mlx4_dev *dev)
priv->cmd.context[priv->cmd.max_cmds - 1].next = -1;
priv->cmd.free_head = 0;
- sema_init(&priv->cmd.event_sem, priv->cmd.max_cmds);
+ init_waitqueue_head(&priv->cmd.event_wait);
+ atomic_set(&priv->cmd.commands, priv->cmd.max_cmds);
spin_lock_init(&priv->cmd.context_lock);
for (priv->cmd.token_mask = 1;
@@ -407,7 +410,8 @@ void mlx4_cmd_use_polling(struct mlx4_dev *dev)
priv->cmd.use_events = 0;
for (i = 0; i < priv->cmd.max_cmds; ++i)
- down(&priv->cmd.event_sem);
+ wait_event(priv->cmd.event_wait,
+ atomic_add_unless(&priv->cmd.commands, -1, 0));
kfree(priv->cmd.context);
diff --git a/drivers/net/ethernet/mellanox/mlx4/mlx4.h b/drivers/net/ethernet/mellanox/mlx4/mlx4.h
index 5dfa68ffc11c..5a2c55d8ccfd 100644
--- a/drivers/net/ethernet/mellanox/mlx4/mlx4.h
+++ b/drivers/net/ethernet/mellanox/mlx4/mlx4.h
@@ -189,7 +189,8 @@ struct mlx4_cmd {
void __iomem *hcr;
struct mutex hcr_mutex;
struct semaphore poll_sem;
- struct semaphore event_sem;
+ wait_queue_head_t event_wait;
+ atomic_t commands;
int max_cmds;
spinlock_t context_lock;
int free_head;
--
2.1.0.rc2
--
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