f2fs: use sbi->write_mutex for write bios

This patch removes an unnecessary semaphore (i.e., sbi->bio_sem).
There is no reason to use the semaphore when f2fs submits read and write IOs.
Instead, let's use a write mutex and cover the sbi->bio[] by the lock.

Change log from v1:
 o split write_mutex suggested by Chao Yu

Chao described,
"All DATA/NODE/META bio buffers in superblock is protected by
'sbi->write_mutex', but each bio buffer area is independent, So we
should split write_mutex to three for DATA/NODE/META."
Signed-off-by: Chao Yu <chao2.yu@samsung.com>
Signed-off-by: Jaegeuk Kim <jaegeuk.kim@samsung.com>

fs/f2fs/data.c

@@ -383,8 +383,6 @@ int f2fs_readpage(struct f2fs_sb_info *sbi, struct page *page,
 
 	trace_f2fs_readpage(page, blk_addr, type);
 
-	down_read(&sbi->bio_sem);
-
 	/* Allocate a new bio */
 	bio = f2fs_bio_alloc(bdev, 1);
 
@@ -394,13 +392,11 @@ int f2fs_readpage(struct f2fs_sb_info *sbi, struct page *page,
 
 	if (bio_add_page(bio, page, PAGE_CACHE_SIZE, 0) < PAGE_CACHE_SIZE) {
 		bio_put(bio);
-		up_read(&sbi->bio_sem);
 		f2fs_put_page(page, 1);
 		return -EFAULT;
 	}
 
 	submit_bio(type, bio);
-	up_read(&sbi->bio_sem);
 	return 0;
 }
 

fs/f2fs/f2fs.h

@@ -374,7 +374,7 @@ struct f2fs_sb_info {
 	struct f2fs_sm_info *sm_info;		/* segment manager */
 	struct bio *bio[NR_PAGE_TYPE];		/* bios to merge */
 	sector_t last_block_in_bio[NR_PAGE_TYPE];	/* last block number */
-	struct rw_semaphore bio_sem;		/* IO semaphore */
+	struct mutex write_mutex[NR_PAGE_TYPE];	/* mutex for writing IOs */
 
 	/* for checkpoint */
 	struct f2fs_checkpoint *ckpt;		/* raw checkpoint pointer */

fs/f2fs/segment.c

@@ -869,9 +869,14 @@ static void do_submit_bio(struct f2fs_sb_info *sbi,
 
 void f2fs_submit_bio(struct f2fs_sb_info *sbi, enum page_type type, bool sync)
 {
-	down_write(&sbi->bio_sem);
+	enum page_type btype = PAGE_TYPE_OF_BIO(type);
+
+	if (!sbi->bio[btype])
+		return;
+
+	mutex_lock(&sbi->write_mutex[btype]);
 	do_submit_bio(sbi, type, sync);
-	up_write(&sbi->bio_sem);
+	mutex_unlock(&sbi->write_mutex[btype]);
 }
 
 static void submit_write_page(struct f2fs_sb_info *sbi, struct page *page,
@@ -882,7 +887,7 @@ static void submit_write_page(struct f2fs_sb_info *sbi, struct page *page,
 
 	verify_block_addr(sbi, blk_addr);
 
-	down_write(&sbi->bio_sem);
+	mutex_lock(&sbi->write_mutex[type]);
 
 	inc_page_count(sbi, F2FS_WRITEBACK);
 
@@ -917,7 +922,7 @@ static void submit_write_page(struct f2fs_sb_info *sbi, struct page *page,
 
 	sbi->last_block_in_bio[type] = blk_addr;
 
-	up_write(&sbi->bio_sem);
+	mutex_unlock(&sbi->write_mutex[type]);
 	trace_f2fs_submit_write_page(page, blk_addr, type);
 }
 

fs/f2fs/super.c

@@ -820,6 +820,7 @@ static int f2fs_fill_super(struct super_block *sb, void *data, int silent)
 	struct buffer_head *raw_super_buf;
 	struct inode *root;
 	long err = -EINVAL;
+	int i;
 
 	/* allocate memory for f2fs-specific super block info */
 	sbi = kzalloc(sizeof(struct f2fs_sb_info), GFP_KERNEL);
@@ -876,7 +877,10 @@ static int f2fs_fill_super(struct super_block *sb, void *data, int silent)
 	mutex_init(&sbi->node_write);
 	sbi->por_doing = false;
 	spin_lock_init(&sbi->stat_lock);
-	init_rwsem(&sbi->bio_sem);
+
+	for (i = 0; i < NR_PAGE_TYPE; i++)
+		mutex_init(&sbi->write_mutex[i]);
+
 	init_rwsem(&sbi->cp_rwsem);
 	init_waitqueue_head(&sbi->cp_wait);
 	init_sb_info(sbi);