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>
diff --git a/drivers/base/dma-contiguous.c b/drivers/base/dma-contiguous.c
index 165c2c2..fe72bac 100644
--- a/drivers/base/dma-contiguous.c
+++ b/drivers/base/dma-contiguous.c
@@ -37,6 +37,7 @@
unsigned long base_pfn;
unsigned long count;
unsigned long *bitmap;
+ struct mutex lock;
};
struct cma *dma_contiguous_default_area;
@@ -161,6 +162,7 @@
init_cma_reserved_pageblock(pfn_to_page(base_pfn));
} while (--i);
+ mutex_init(&cma->lock);
return 0;
}
@@ -261,6 +263,13 @@
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 @@
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 @@
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;
}