cma: Remove potential deadlock situation

CMA locking is currently very coarse. The cma_mutex protects both
the bitmap and avoids concurrency with alloc_contig_range. There
are several situations which may result in a deadlock on the CMA
mutex currently, mostly involving AB/BA situations with alloc and
free. Fix this issue by protecting the bitmap with a mutex per CMA
region and use the existing mutex for protecting against concurrency
with alloc_contig_range.

Signed-off-by: Laura Abbott <lauraa@codeaurora.org>
Signed-off-by: Marek Szyprowski <m.szyprowski@samsung.com>

1 files changed, 25 insertions, 7 deletions

diff --git a/drivers/base/dma-contiguous.c b/drivers/base/dma-contiguous.c
index 165c2c299e57..fe72bac96275 100644
--- a/drivers/base/dma-contiguous.c
+++ b/drivers/base/dma-contiguous.c
@@ -37,6 +37,7 @@ struct cma {
         unsigned long   base_pfn;
         unsigned long   count;
         unsigned long   *bitmap;
+        struct mutex    lock;
 };
 
 struct cma *dma_contiguous_default_area;
@@ -161,6 +162,7 @@ static int __init cma_activate_area(struct cma *cma)
                 init_cma_reserved_pageblock(pfn_to_page(base_pfn));
         } while (--i);
 
+        mutex_init(&cma->lock);
         return 0;
 }
 
@@ -261,6 +263,13 @@ err:
         return ret;
 }
 
+static void clear_cma_bitmap(struct cma *cma, unsigned long pfn, int count)
+{
+        mutex_lock(&cma->lock);
+        bitmap_clear(cma->bitmap, pfn - cma->base_pfn, count);
+        mutex_unlock(&cma->lock);
+}
+
 /**
  * dma_alloc_from_contiguous() - allocate pages from contiguous area
  * @dev:   Pointer to device for which the allocation is performed.
@@ -294,30 +303,41 @@ struct page *dma_alloc_from_contiguous(struct device *dev, int count,
 
         mask = (1 << align) - 1;
 
-        mutex_lock(&cma_mutex);
 
         for (;;) {
+                mutex_lock(&cma->lock);
                 pageno = bitmap_find_next_zero_area(cma->bitmap, cma->count,
                                                     start, count, mask);
-                if (pageno >= cma->count)
+                if (pageno >= cma->count) {
+                        mutex_unlock(&cma_mutex);
                         break;
+                }
+                bitmap_set(cma->bitmap, pageno, count);
+                /*
+                 * It's safe to drop the lock here. We've marked this region for
+                 * our exclusive use. If the migration fails we will take the
+                 * lock again and unmark it.
+                 */
+                mutex_unlock(&cma->lock);
 
                 pfn = cma->base_pfn + pageno;
+                mutex_lock(&cma_mutex);
                 ret = alloc_contig_range(pfn, pfn + count, MIGRATE_CMA);
+                mutex_unlock(&cma_mutex);
                 if (ret == 0) {
-                        bitmap_set(cma->bitmap, pageno, count);
                         page = pfn_to_page(pfn);
                         break;
                 } else if (ret != -EBUSY) {
+                        clear_cma_bitmap(cma, pfn, count);
                         break;
                 }
+                clear_cma_bitmap(cma, pfn, count);
                 pr_debug("%s(): memory range at %p is busy, retrying\n",
                          __func__, pfn_to_page(pfn));
                 /* try again with a bit different memory target */
                 start = pageno + mask + 1;
         }
 
-        mutex_unlock(&cma_mutex);
         pr_debug("%s(): returned %p\n", __func__, page);
         return page;
 }
@@ -350,10 +370,8 @@ bool dma_release_from_contiguous(struct device *dev, struct page *pages,
 
         VM_BUG_ON(pfn + count > cma->base_pfn + cma->count);
 
-        mutex_lock(&cma_mutex);
-        bitmap_clear(cma->bitmap, pfn - cma->base_pfn, count);
         free_contig_range(pfn, count);
-        mutex_unlock(&cma_mutex);
+        clear_cma_bitmap(cma, pfn, count);
 
         return true;
 }