[PATCH v4 1/2] exfat: introduce bitmap_lock for cluster bitmap access

[Hyeongseok Kim <hyeongseok@xxxxxxxxx>]

s_lock which is for protecting concurrent access of file operations is
too huge for cluster bitmap protection, so introduce a new bitmap_lock
to narrow the lock range if only need to access cluster bitmap.

Signed-off-by: Hyeongseok Kim <hyeongseok@xxxxxxxxx>
---
 fs/exfat/exfat_fs.h |  1 +
 fs/exfat/fatent.c   | 37 +++++++++++++++++++++++++++++--------
 fs/exfat/super.c    |  1 +
 3 files changed, 31 insertions(+), 8 deletions(-)

diff --git a/fs/exfat/exfat_fs.h b/fs/exfat/exfat_fs.h
index 764bc645241e..1ce422d7e9ae 100644
--- a/fs/exfat/exfat_fs.h
+++ b/fs/exfat/exfat_fs.h
@@ -238,6 +238,7 @@ struct exfat_sb_info {
 	unsigned int used_clusters; /* number of used clusters */
 
 	struct mutex s_lock; /* superblock lock */
+	struct mutex bitmap_lock; /* bitmap lock */
 	struct exfat_mount_options options;
 	struct nls_table *nls_io; /* Charset used for input and display */
 	struct ratelimit_state ratelimit;
diff --git a/fs/exfat/fatent.c b/fs/exfat/fatent.c
index 7b2e8af17193..fd6c7fd12762 100644
--- a/fs/exfat/fatent.c
+++ b/fs/exfat/fatent.c
@@ -151,13 +151,14 @@ int exfat_chain_cont_cluster(struct super_block *sb, unsigned int chain,
 	return 0;
 }
 
-int exfat_free_cluster(struct inode *inode, struct exfat_chain *p_chain)
+/* This function must be called with bitmap_lock held */
+static int __exfat_free_cluster(struct inode *inode, struct exfat_chain *p_chain)
 {
-	unsigned int num_clusters = 0;
-	unsigned int clu;
 	struct super_block *sb = inode->i_sb;
 	struct exfat_sb_info *sbi = EXFAT_SB(sb);
 	int cur_cmap_i, next_cmap_i;
+	unsigned int num_clusters = 0;
+	unsigned int clu;
 
 	/* invalid cluster number */
 	if (p_chain->dir == EXFAT_FREE_CLUSTER ||
@@ -230,6 +231,17 @@ int exfat_free_cluster(struct inode *inode, struct exfat_chain *p_chain)
 	return 0;
 }
 
+int exfat_free_cluster(struct inode *inode, struct exfat_chain *p_chain)
+{
+	int ret = 0;
+
+	mutex_lock(&EXFAT_SB(inode->i_sb)->bitmap_lock);
+	ret = __exfat_free_cluster(inode, p_chain);
+	mutex_unlock(&EXFAT_SB(inode->i_sb)->bitmap_lock);
+
+	return ret;
+}
+
 int exfat_find_last_cluster(struct super_block *sb, struct exfat_chain *p_chain,
 		unsigned int *ret_clu)
 {
@@ -328,6 +340,8 @@ int exfat_alloc_cluster(struct inode *inode, unsigned int num_alloc,
 	if (num_alloc > total_cnt - sbi->used_clusters)
 		return -ENOSPC;
 
+	mutex_lock(&sbi->bitmap_lock);
+
 	hint_clu = p_chain->dir;
 	/* find new cluster */
 	if (hint_clu == EXFAT_EOF_CLUSTER) {
@@ -338,8 +352,10 @@ int exfat_alloc_cluster(struct inode *inode, unsigned int num_alloc,
 		}
 
 		hint_clu = exfat_find_free_bitmap(sb, sbi->clu_srch_ptr);
-		if (hint_clu == EXFAT_EOF_CLUSTER)
-			return -ENOSPC;
+		if (hint_clu == EXFAT_EOF_CLUSTER) {
+			ret = -ENOSPC;
+			goto unlock;
+		}
 	}
 
 	/* check cluster validation */
@@ -349,8 +365,10 @@ int exfat_alloc_cluster(struct inode *inode, unsigned int num_alloc,
 		hint_clu = EXFAT_FIRST_CLUSTER;
 		if (p_chain->flags == ALLOC_NO_FAT_CHAIN) {
 			if (exfat_chain_cont_cluster(sb, p_chain->dir,
-					num_clusters))
-				return -EIO;
+					num_clusters)) {
+				ret = -EIO;
+				goto unlock;
+			}
 			p_chain->flags = ALLOC_FAT_CHAIN;
 		}
 	}
@@ -400,6 +418,7 @@ int exfat_alloc_cluster(struct inode *inode, unsigned int num_alloc,
 			sbi->used_clusters += num_clusters;
 
 			p_chain->size += num_clusters;
+			mutex_unlock(&sbi->bitmap_lock);
 			return 0;
 		}
 
@@ -419,7 +438,9 @@ int exfat_alloc_cluster(struct inode *inode, unsigned int num_alloc,
 	}
 free_cluster:
 	if (num_clusters)
-		exfat_free_cluster(inode, p_chain);
+		__exfat_free_cluster(inode, p_chain);
+unlock:
+	mutex_unlock(&sbi->bitmap_lock);
 	return ret;
 }
 
diff --git a/fs/exfat/super.c b/fs/exfat/super.c
index c6d8d2e53486..d38d17a77e76 100644
--- a/fs/exfat/super.c
+++ b/fs/exfat/super.c
@@ -752,6 +752,7 @@ static int exfat_init_fs_context(struct fs_context *fc)
 		return -ENOMEM;
 
 	mutex_init(&sbi->s_lock);
+	mutex_init(&sbi->bitmap_lock);
 	ratelimit_state_init(&sbi->ratelimit, DEFAULT_RATELIMIT_INTERVAL,
 			DEFAULT_RATELIMIT_BURST);
 
-- 
2.27.0.83.g0313f36