cw1200: Prevent a lock-related hang in the cw1200_spi driver

The cw1200_spi driver tries to mirror the cw1200_sdio driver's lock
API, which relies on sdio_claim_host/sdio_release_host to serialize
hardware operations across multiple threads.

Unfortunately the implementation was flawed, as it lacked a way to wake
up the lock requestor when there was contention, often resulting in a
hang.

This problem was uncovered while trying to fix the
spi-transfers-in-interrupt-context BUG() corrected in the previous
patch.  Many thanks to Dave Sizeburns for his assistance in fixing this.

Signed-off-by: Solomon Peachy <pizza@shaftnet.org>
Signed-off-by: John W. Linville <linville@tuxdriver.com>

1 files changed, 9 insertions, 0 deletions

diff --git a/drivers/net/wireless/cw1200/cw1200_spi.c b/drivers/net/wireless/cw1200/cw1200_spi.c
index c31580ba883b..f5e6b489ed32 100644
--- a/drivers/net/wireless/cw1200/cw1200_spi.c
+++ b/drivers/net/wireless/cw1200/cw1200_spi.c
@@ -40,6 +40,7 @@ struct hwbus_priv {
         struct cw1200_common    *core;
         const struct cw1200_platform_data_spi *pdata;
         spinlock_t              lock; /* Serialize all bus operations */
+        wait_queue_head_t       wq;
         int claimed;
         int irq_disabled;
 };
@@ -198,8 +199,11 @@ static void cw1200_spi_lock(struct hwbus_priv *self)
 {
         unsigned long flags;
 
+        DECLARE_WAITQUEUE(wait, current);
+
         might_sleep();
 
+        add_wait_queue(&self->wq, &wait);
         spin_lock_irqsave(&self->lock, flags);
         while (1) {
                 set_current_state(TASK_UNINTERRUPTIBLE);
@@ -212,6 +216,7 @@ static void cw1200_spi_lock(struct hwbus_priv *self)
         set_current_state(TASK_RUNNING);
         self->claimed = 1;
         spin_unlock_irqrestore(&self->lock, flags);
+        remove_wait_queue(&self->wq, &wait);
 
         return;
 }
@@ -223,6 +228,8 @@ static void cw1200_spi_unlock(struct hwbus_priv *self)
         spin_lock_irqsave(&self->lock, flags);
         self->claimed = 0;
         spin_unlock_irqrestore(&self->lock, flags);
+        wake_up(&self->wq);
+
         return;
 }
 
@@ -413,6 +420,8 @@ static int cw1200_spi_probe(struct spi_device *func)
 
         spi_set_drvdata(func, self);
 
+        init_waitqueue_head(&self->wq);
+
         status = cw1200_spi_irq_subscribe(self);
 
         status = cw1200_core_probe(&cw1200_spi_hwbus_ops,