[PATCH 6.1.y 1/2] exfat: support dynamic allocate bh for exfat_entry_set_cache

[Harshit Mogalapalli <harshit.m.mogalapalli@xxxxxxxxxx>]

From: Yuezhang Mo <Yuezhang.Mo@xxxxxxxx>

[ Upstream commit a3ff29a95fde16906304455aa8c0bd84eb770258 ]

In special cases, a file or a directory may occupied more than 19
directory entries, pre-allocating 3 bh is not enough. Such as
  - Support vendor secondary directory entry in the future.
  - Since file directory entry is damaged, the SecondaryCount
    field is bigger than 18.

So this commit supports dynamic allocation of bh.

Signed-off-by: Yuezhang Mo <Yuezhang.Mo@xxxxxxxx>
Reviewed-by: Andy Wu <Andy.Wu@xxxxxxxx>
Reviewed-by: Aoyama Wataru <wataru.aoyama@xxxxxxxx>
Reviewed-by: Sungjong Seo <sj1557.seo@xxxxxxxxxxx>
Signed-off-by: Namjae Jeon <linkinjeon@xxxxxxxxxx>
(cherry picked from commit a3ff29a95fde16906304455aa8c0bd84eb770258)
[Harshit: Backport - clean cherry-pick to 6.1.y]
Signed-off-by: Harshit Mogalapalli <harshit.m.mogalapalli@xxxxxxxxxx>
---
This is already in 5.10.y and 5.15.y, let us apply this to 6.1.y, this
also has a fix commit: 89fc548767a2 ("exfat: fix potential deadlock on
__exfat_get_dentry_set"). Both apply cleanly on 6.1.y and builds fine.
No exfat specific testing is done.
---
 fs/exfat/dir.c      | 15 +++++++++++++++
 fs/exfat/exfat_fs.h |  5 ++++-
 2 files changed, 19 insertions(+), 1 deletion(-)

diff --git a/fs/exfat/dir.c b/fs/exfat/dir.c
index 51b03b0dd5f7..6fd9a06cc7d0 100644
--- a/fs/exfat/dir.c
+++ b/fs/exfat/dir.c
@@ -613,6 +613,10 @@ int exfat_free_dentry_set(struct exfat_entry_set_cache *es, int sync)
 			bforget(es->bh[i]);
 		else
 			brelse(es->bh[i]);
+
+	if (IS_DYNAMIC_ES(es))
+		kfree(es->bh);
+
 	kfree(es);
 	return err;
 }
@@ -845,6 +849,7 @@ struct exfat_entry_set_cache *exfat_get_dentry_set(struct super_block *sb,
 	/* byte offset in sector */
 	off = EXFAT_BLK_OFFSET(byte_offset, sb);
 	es->start_off = off;
+	es->bh = es->__bh;
 
 	/* sector offset in cluster */
 	sec = EXFAT_B_TO_BLK(byte_offset, sb);
@@ -864,6 +869,16 @@ struct exfat_entry_set_cache *exfat_get_dentry_set(struct super_block *sb,
 	es->num_entries = num_entries;
 
 	num_bh = EXFAT_B_TO_BLK_ROUND_UP(off + num_entries * DENTRY_SIZE, sb);
+	if (num_bh > ARRAY_SIZE(es->__bh)) {
+		es->bh = kmalloc_array(num_bh, sizeof(*es->bh), GFP_KERNEL);
+		if (!es->bh) {
+			brelse(bh);
+			kfree(es);
+			return NULL;
+		}
+		es->bh[0] = bh;
+	}
+
 	for (i = 1; i < num_bh; i++) {
 		/* get the next sector */
 		if (exfat_is_last_sector_in_cluster(sbi, sec)) {
diff --git a/fs/exfat/exfat_fs.h b/fs/exfat/exfat_fs.h
index e0af6ace633c..c79c78bf265b 100644
--- a/fs/exfat/exfat_fs.h
+++ b/fs/exfat/exfat_fs.h
@@ -169,10 +169,13 @@ struct exfat_entry_set_cache {
 	bool modified;
 	unsigned int start_off;
 	int num_bh;
-	struct buffer_head *bh[DIR_CACHE_SIZE];
+	struct buffer_head *__bh[DIR_CACHE_SIZE];
+	struct buffer_head **bh;
 	unsigned int num_entries;
 };
 
+#define IS_DYNAMIC_ES(es)	((es)->__bh != (es)->bh)
+
 struct exfat_dir_entry {
 	struct exfat_chain dir;
 	int entry;
-- 
2.46.0