debugfs: make sure we can remove u32_array files cleanly

debugfs_create_u32_array() allocates a small structure to wrap
the data and size information about the array. If users ever
try to remove the file this leads to a leak since nothing ever
frees this wrapper.

That said there are no upstream users of debugfs_create_u32_array()
that'd remove a u32 array file (we only have one u32 array user in
CMA), so there is no real bug here.

Make callers pass a wrapper they allocated. This way the lifetime
management of the wrapper is on the caller, and we can avoid the
potential leak in debugfs.

CC: Chucheng Luo <luochucheng@vivo.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

2 files changed, 7 insertions, 3 deletions

diff --git a/mm/cma.h b/mm/cma.h
index 33c0b517733c..6698fa63279b 100644
--- a/mm/cma.h
+++ b/mm/cma.h
@@ -2,6 +2,8 @@
 #ifndef __MM_CMA_H__
 #define __MM_CMA_H__
 
+#include <linux/debugfs.h>
+
 struct cma {
 	unsigned long   base_pfn;
 	unsigned long   count;
@@ -11,6 +13,7 @@ struct cma {
 #ifdef CONFIG_CMA_DEBUGFS
 	struct hlist_head mem_head;
 	spinlock_t mem_head_lock;
+	struct debugfs_u32_array dfs_bitmap;
 #endif
 	const char *name;
 };
diff --git a/mm/cma_debug.c b/mm/cma_debug.c
index 4e6cbe2f586e..d5bf8aa34fdc 100644
--- a/mm/cma_debug.c
+++ b/mm/cma_debug.c
@@ -164,7 +164,6 @@ static void cma_debugfs_add_one(struct cma *cma, struct dentry *root_dentry)
 {
 	struct dentry *tmp;
 	char name[16];
-	int u32s;
 
 	scnprintf(name, sizeof(name), "cma-%s", cma->name);
 
@@ -180,8 +179,10 @@ static void cma_debugfs_add_one(struct cma *cma, struct dentry *root_dentry)
 	debugfs_create_file("used", 0444, tmp, cma, &cma_used_fops);
 	debugfs_create_file("maxchunk", 0444, tmp, cma, &cma_maxchunk_fops);
 
-	u32s = DIV_ROUND_UP(cma_bitmap_maxno(cma), BITS_PER_BYTE * sizeof(u32));
-	debugfs_create_u32_array("bitmap", 0444, tmp, (u32 *)cma->bitmap, u32s);
+	cma->dfs_bitmap.array = (u32 *)cma->bitmap;
+	cma->dfs_bitmap.n_elements = DIV_ROUND_UP(cma_bitmap_maxno(cma),
+						  BITS_PER_BYTE * sizeof(u32));
+	debugfs_create_u32_array("bitmap", 0444, tmp, &cma->dfs_bitmap);
 }
 
 static int __init cma_debugfs_init(void)