[PATCH v4 02/10] IB/core: Replace semaphore sm_sem with an atomic wait

[Binoy Jayan]

The semaphore 'sm_sem' is used for an exclusive ownership of the device
so model the same as an atomic variable with an associated wait_event.
Semaphores are going away in the future.

Signed-off-by: Binoy Jayan <binoy.ja...@linaro.org>
---
 drivers/infiniband/core/user_mad.c | 20 ++++++++++++++------
 1 file changed, 14 insertions(+), 6 deletions(-)

diff --git a/drivers/infiniband/core/user_mad.c 
b/drivers/infiniband/core/user_mad.c
index 415a318..6101c0a 100644
--- a/drivers/infiniband/core/user_mad.c
+++ b/drivers/infiniband/core/user_mad.c
@@ -67,6 +67,8 @@ enum {
        IB_UMAD_MINOR_BASE = 0
 };
 
+#define UMAD_F_CLAIM   0x01
+
 /*
  * Our lifetime rules for these structs are the following:
  * device special file is opened, we take a reference on the
@@ -87,7 +89,8 @@ struct ib_umad_port {
 
        struct cdev           sm_cdev;
        struct device         *sm_dev;
-       struct semaphore       sm_sem;
+       wait_queue_head_t     wq;
+       unsigned long         flags;
 
        struct mutex           file_mutex;
        struct list_head       file_list;
@@ -1030,12 +1033,14 @@ static int ib_umad_sm_open(struct inode *inode, struct 
file *filp)
        port = container_of(inode->i_cdev, struct ib_umad_port, sm_cdev);
 
        if (filp->f_flags & O_NONBLOCK) {
-               if (down_trylock(&port->sm_sem)) {
+               if (test_and_set_bit(UMAD_F_CLAIM, &port->flags)) {
                        ret = -EAGAIN;
                        goto fail;
                }
        } else {
-               if (down_interruptible(&port->sm_sem)) {
+               if (wait_event_interruptible(port->wq,
+                                            !test_and_set_bit(UMAD_F_CLAIM,
+                                            &port->flags))) {
                        ret = -ERESTARTSYS;
                        goto fail;
                }
@@ -1060,7 +1065,8 @@ static int ib_umad_sm_open(struct inode *inode, struct 
file *filp)
        ib_modify_port(port->ib_dev, port->port_num, 0, &props);
 
 err_up_sem:
-       up(&port->sm_sem);
+       clear_bit(UMAD_F_CLAIM, &port->flags);
+       wake_up(&port->wq);
 
 fail:
        return ret;
@@ -1079,7 +1085,8 @@ static int ib_umad_sm_close(struct inode *inode, struct 
file *filp)
                ret = ib_modify_port(port->ib_dev, port->port_num, 0, &props);
        mutex_unlock(&port->file_mutex);
 
-       up(&port->sm_sem);
+       clear_bit(UMAD_F_CLAIM, &port->flags);
+       wake_up(&port->wq);
 
        kobject_put(&port->umad_dev->kobj);
 
@@ -1177,7 +1184,8 @@ static int ib_umad_init_port(struct ib_device *device, 
int port_num,
 
        port->ib_dev   = device;
        port->port_num = port_num;
-       sema_init(&port->sm_sem, 1);
+       init_waitqueue_head(&port->wq);
+       __clear_bit(UMAD_F_CLAIM, &port->flags);
        mutex_init(&port->file_mutex);
        INIT_LIST_HEAD(&port->file_list);
 
-- 
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