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Commit 7ee793a6 authored by Laura Abbott's avatar Laura Abbott Committed by Marek Szyprowski
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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: default avatarLaura Abbott <lauraa@codeaurora.org>
Signed-off-by: default avatarMarek Szyprowski <m.szyprowski@samsung.com>
parent d6d211db

drivers/base/dma-contiguous.c

+25 −7
Original line number Original line Diff line number Diff line
@@ -37,6 +37,7 @@ struct cma { 
	unsigned long	base_pfn;

	unsigned long	base_pfn;

	unsigned long	count;

	unsigned long	count;

	unsigned long	*bitmap;

	unsigned long	*bitmap;

	struct mutex	lock;

};

};





struct cma *dma_contiguous_default_area;

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));

		init_cma_reserved_pageblock(pfn_to_page(base_pfn));

	} while (--i);

	} while (--i);





	mutex_init(&cma->lock);

	return 0;

	return 0;

}

}
@@ -261,6 +263,13 @@ int __init dma_contiguous_reserve_area(phys_addr_t size, phys_addr_t base, 
	return ret;

	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

 * dma_alloc_from_contiguous() - allocate pages from contiguous area

 * @dev:   Pointer to device for which the allocation is performed.

 * @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;

	mask = (1 << align) - 1;





	mutex_lock(&cma_mutex);





	for (;;) {

	for (;;) {

		mutex_lock(&cma->lock);

		pageno = bitmap_find_next_zero_area(cma->bitmap, cma->count,

		pageno = bitmap_find_next_zero_area(cma->bitmap, cma->count,

						    start, count, mask);

						    start, count, mask);

		if (pageno >= cma->count)

		if (pageno >= cma->count) {

			mutex_unlock(&cma_mutex);

			break;

			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;

		pfn = cma->base_pfn + pageno;

		mutex_lock(&cma_mutex);

		ret = alloc_contig_range(pfn, pfn + count, MIGRATE_CMA);

		ret = alloc_contig_range(pfn, pfn + count, MIGRATE_CMA);

		mutex_unlock(&cma_mutex);

		if (ret == 0) {

		if (ret == 0) {

			bitmap_set(cma->bitmap, pageno, count);

			page = pfn_to_page(pfn);

			page = pfn_to_page(pfn);

			break;

			break;

		} else if (ret != -EBUSY) {

		} else if (ret != -EBUSY) {

			clear_cma_bitmap(cma, pfn, count);

			break;

			break;

		}

		}

		clear_cma_bitmap(cma, pfn, count);

		pr_debug("%s(): memory range at %p is busy, retrying\n",

		pr_debug("%s(): memory range at %p is busy, retrying\n",

			 __func__, pfn_to_page(pfn));

			 __func__, pfn_to_page(pfn));

		/* try again with a bit different memory target */

		/* try again with a bit different memory target */

		start = pageno + mask + 1;

		start = pageno + mask + 1;

	}

	}





	mutex_unlock(&cma_mutex);

	pr_debug("%s(): returned %p\n", __func__, page);

	pr_debug("%s(): returned %p\n", __func__, page);

	return 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);

	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);

	free_contig_range(pfn, count);

	mutex_unlock(&cma_mutex);

	clear_cma_bitmap(cma, pfn, count);





	return true;

	return true;

}
 
}