mm/cma: add API to enable concurrent allocation from the CMA

hygon inclusion
category: feature
CVE: NA

---------------------------

The mutex prevents allocating CMA memory concurently, and it's
removed and reverted back and forth, refer to commit 60a60e3
("Revert "mm/cma.c: remove redundant cma_mutex lock"") and commit
a4efc17 ("mm/cma.c: remove redundant cma_mutex lock") in
the upstream.

To solve the awkward dilemma, an API to enable concurrency is added,
it's up to user to decide whether their CMA can handle concurrent
allocations.

Signed-off-by: Yangwencheng <[email protected]>
Signed-off-by: Xin Jiang <[email protected]>
Signed-off-by: hanliyang <[email protected]>

Author: Xin Jiang

include/linux/cma.h

@@ -58,4 +58,5 @@ extern int cma_for_each_area(int (*it)(struct cma *cma, void *data), void *data)
 extern void cma_reserve_pages_on_error(struct cma *cma);
 
 extern int __init cma_alloc_areas(unsigned int max_cma_size);
+extern void cma_enable_concurrency(struct cma *cma);
 #endif

mm/cma.c

@@ -492,10 +492,12 @@ struct page *cma_alloc(struct cma *cma, unsigned long count,
 		spin_unlock_irq(&cma->lock);
 
 		pfn = cma->base_pfn + (bitmap_no << cma->order_per_bit);
-		mutex_lock(&cma_mutex);
+		if (!cma->no_mutex)
+			mutex_lock(&cma_mutex);
 		ret = alloc_contig_range(pfn, pfn + count, MIGRATE_CMA,
 				     GFP_KERNEL | (no_warn ? __GFP_NOWARN : 0));
-		mutex_unlock(&cma_mutex);
+		if (!cma->no_mutex)
+			mutex_unlock(&cma_mutex);
 		if (ret == 0) {
 			page = pfn_to_page(pfn);
 			break;
@@ -609,3 +611,11 @@ int cma_for_each_area(int (*it)(struct cma *cma, void *data), void *data)
 
 	return 0;
 }
+
+void cma_enable_concurrency(struct cma *cma)
+{
+	if (!cma)
+		return;
+
+	cma->no_mutex = true;
+}

mm/cma.h

@@ -16,6 +16,7 @@ struct cma {
 	unsigned long   *bitmap;
 	unsigned int order_per_bit; /* Order of pages represented by one bit */
 	spinlock_t	lock;
+	bool no_mutex;
 #ifdef CONFIG_CMA_DEBUGFS
 	struct hlist_head mem_head;
 	spinlock_t mem_head_lock;