[PATCH 001/001] mmcblk: Fix deadlock when cleanup is called from resume

[san@google.com (San Mehat)]

  When CONFIG_UNSAFE_RESUME is used, we may need to cleanup
  (and call kthread_stop) when threads are still frozen. To fix this
  deadlock, push cleanup off to a work-queue.

  Signed-off-by: San Mehat <san@android.com>

---
 drivers/mmc/card/queue.c |   36 ++++++++++++++++++++++++++++++++++--
 1 files changed, 34 insertions(+), 2 deletions(-)

diff --git a/drivers/mmc/card/queue.c b/drivers/mmc/card/queue.c
index 972738f..908e3cf 100644
--- a/drivers/mmc/card/queue.c
+++ b/drivers/mmc/card/queue.c
@@ -14,6 +14,7 @@
 #include <linux/freezer.h>
 #include <linux/kthread.h>
 #include <linux/scatterlist.h>
+#include <linux/workqueue.h>
 
 #include <linux/mmc/card.h>
 #include <linux/mmc/host.h>
@@ -23,6 +24,11 @@
 
 #define MMC_QUEUE_SUSPENDED	(1 << 0)
 
+static void mq_cleanup_work(struct work_struct *work);
+static DECLARE_WORK(mq_cleanup_worker, mq_cleanup_work);
+static struct mmc_queue *cleanup_mq;
+static DEFINE_SPINLOCK(mq_cleanup_lock);
+
 /*
  * Prepare a MMC request. This just filters out odd stuff.
  */
@@ -217,9 +223,36 @@ int mmc_init_queue(struct mmc_queue *mq, struct mmc_card *card, spinlock_t *lock
 
 void mmc_cleanup_queue(struct mmc_queue *mq)
 {
-	struct request_queue *q = mq->queue;
 	unsigned long flags;
 
+	BUG_ON(!mq);
+
+	/*
+	 * The actual cleanup is done from a work_queue because if you
+	 * thread_stop() while resuming, you'll deadlock.
+	 */
+	spin_lock_irqsave(&mq_cleanup_lock, flags);
+	cleanup_mq = mq;
+	schedule_work(&mq_cleanup_worker);
+	spin_unlock_irqrestore(&mq_cleanup_lock, flags);
+}
+EXPORT_SYMBOL(mmc_cleanup_queue);
+
+static void mq_cleanup_work(struct work_struct *work)
+{
+	struct mmc_queue *mq;
+	unsigned long flags;
+	struct request_queue *q;
+
+	spin_lock_irqsave(&mq_cleanup_lock, flags);
+	mq = cleanup_mq;
+	cleanup_mq = NULL;
+	spin_unlock_irqrestore(&mq_cleanup_lock, flags);
+
+	BUG_ON(!mq);
+
+	q = mq->queue;
+
 	/* Mark that we should start throwing out stragglers */
 	spin_lock_irqsave(q->queue_lock, flags);
 	q->queuedata = NULL;
@@ -246,7 +279,6 @@ void mmc_cleanup_queue(struct mmc_queue *mq)
 
 	mq->card = NULL;
 }
-EXPORT_SYMBOL(mmc_cleanup_queue);
 
 /**
  * mmc_queue_suspend - suspend a MMC request queue