dmar: use spin_lock_irqsave() in qi_submit_sync()

Next patch in the series will use queued invalidation interface
qi_submit_sync() for DMA-remapping aswell, which can be called from interrupt
context.

So use spin_lock_irqsave() instead of spin_lock() in qi_submit_sync().

Signed-off-by: Suresh Siddha <suresh.b.siddha@intel.com>
Signed-off-by: Youquan Song <youquan.song@intel.com>
Signed-off-by: David Woodhouse <David.Woodhouse@intel.com>

1 files changed, 13 insertions, 6 deletions

diff --git a/drivers/pci/dmar.c b/drivers/pci/dmar.c
index e842e756308a..b64cec190542 100644
--- a/drivers/pci/dmar.c
+++ b/drivers/pci/dmar.c
@@ -580,11 +580,11 @@ void qi_submit_sync(struct qi_desc *desc, struct intel_iommu *iommu)
 
         hw = qi->desc;
 
-        spin_lock(&qi->q_lock);
+        spin_lock_irqsave(&qi->q_lock, flags);
         while (qi->free_cnt < 3) {
-                spin_unlock(&qi->q_lock);
+                spin_unlock_irqrestore(&qi->q_lock, flags);
                 cpu_relax();
-                spin_lock(&qi->q_lock);
+                spin_lock_irqsave(&qi->q_lock, flags);
         }
 
         index = qi->free_head;
@@ -605,15 +605,22 @@ void qi_submit_sync(struct qi_desc *desc, struct intel_iommu *iommu)
         qi->free_head = (qi->free_head + 2) % QI_LENGTH;
         qi->free_cnt -= 2;
 
-        spin_lock_irqsave(&iommu->register_lock, flags);
+        spin_lock(&iommu->register_lock);
         /*
          * update the HW tail register indicating the presence of
          * new descriptors.
          */
         writel(qi->free_head << 4, iommu->reg + DMAR_IQT_REG);
-        spin_unlock_irqrestore(&iommu->register_lock, flags);
+        spin_unlock(&iommu->register_lock);
 
         while (qi->desc_status[wait_index] != QI_DONE) {
+                /*
+                 * We will leave the interrupts disabled, to prevent interrupt
+                 * context to queue another cmd while a cmd is already submitted
+                 * and waiting for completion on this cpu. This is to avoid
+                 * a deadlock where the interrupt context can wait indefinitely
+                 * for free slots in the queue.
+                 */
                 spin_unlock(&qi->q_lock);
                 cpu_relax();
                 spin_lock(&qi->q_lock);
@@ -622,7 +629,7 @@ void qi_submit_sync(struct qi_desc *desc, struct intel_iommu *iommu)
         qi->desc_status[index] = QI_DONE;
 
         reclaim_free_desc(qi);
-        spin_unlock(&qi->q_lock);
+        spin_unlock_irqrestore(&qi->q_lock, flags);
 }
 
 /*