[RFC PATCH v4 1/8] ext4: convert i_fc_lock to spinlock

[Harshad Shirwadkar <harshadshirwadkar@xxxxxxxxx>]

Convert ext4_inode_info->i_fc_lock to spinlock to avoid sleeping
in invalid contexts.

Signed-off-by: Harshad Shirwadkar <harshadshirwadkar@xxxxxxxxx>
Reviewed-by: Jan Kara <jack@xxxxxxx>
---
 fs/ext4/ext4.h        |  7 +++++--
 fs/ext4/fast_commit.c | 22 ++++++++++------------
 fs/ext4/super.c       |  2 +-
 3 files changed, 16 insertions(+), 15 deletions(-)

diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h
index 75b8d81b2469..12c8691f08d3 100644
--- a/fs/ext4/ext4.h
+++ b/fs/ext4/ext4.h
@@ -1067,8 +1067,11 @@ struct ext4_inode_info {
 	/* Fast commit wait queue for this inode */
 	wait_queue_head_t i_fc_wait;
 
-	/* Protect concurrent accesses on i_fc_lblk_start, i_fc_lblk_len */
-	struct mutex i_fc_lock;
+	/*
+	 * Protect concurrent accesses on i_fc_lblk_start, i_fc_lblk_len
+	 * and inode's EXT4_FC_STATE_COMMITTING state bit.
+	 */
+	spinlock_t i_fc_lock;
 
 	/*
 	 * i_disksize keeps track of what the inode size is ON DISK, not
diff --git a/fs/ext4/fast_commit.c b/fs/ext4/fast_commit.c
index 795a60ad1897..8d6d5155a646 100644
--- a/fs/ext4/fast_commit.c
+++ b/fs/ext4/fast_commit.c
@@ -380,7 +380,7 @@ static int ext4_fc_track_template(
 	int ret;
 
 	tid = handle->h_transaction->t_tid;
-	mutex_lock(&ei->i_fc_lock);
+	spin_lock(&ei->i_fc_lock);
 	if (tid == ei->i_sync_tid) {
 		update = true;
 	} else {
@@ -388,7 +388,7 @@ static int ext4_fc_track_template(
 		ei->i_sync_tid = tid;
 	}
 	ret = __fc_track_fn(inode, args, update);
-	mutex_unlock(&ei->i_fc_lock);
+	spin_unlock(&ei->i_fc_lock);
 
 	if (!enqueue)
 		return ret;
@@ -420,11 +420,11 @@ static int __track_dentry_update(struct inode *inode, void *arg, bool update)
 	struct dentry *dentry = dentry_update->dentry;
 	struct ext4_sb_info *sbi = EXT4_SB(inode->i_sb);
 
-	mutex_unlock(&ei->i_fc_lock);
+	spin_unlock(&ei->i_fc_lock);
 	node = kmem_cache_alloc(ext4_fc_dentry_cachep, GFP_NOFS);
 	if (!node) {
 		ext4_fc_mark_ineligible(inode->i_sb, EXT4_FC_REASON_NOMEM, NULL);
-		mutex_lock(&ei->i_fc_lock);
+		spin_lock(&ei->i_fc_lock);
 		return -ENOMEM;
 	}
 
@@ -437,7 +437,7 @@ static int __track_dentry_update(struct inode *inode, void *arg, bool update)
 			kmem_cache_free(ext4_fc_dentry_cachep, node);
 			ext4_fc_mark_ineligible(inode->i_sb,
 				EXT4_FC_REASON_NOMEM, NULL);
-			mutex_lock(&ei->i_fc_lock);
+			spin_lock(&ei->i_fc_lock);
 			return -ENOMEM;
 		}
 		memcpy((u8 *)node->fcd_name.name, dentry->d_name.name,
@@ -471,7 +471,7 @@ static int __track_dentry_update(struct inode *inode, void *arg, bool update)
 		list_add_tail(&node->fcd_dilist, &ei->i_fc_dilist);
 	}
 	spin_unlock(&sbi->s_fc_lock);
-	mutex_lock(&ei->i_fc_lock);
+	spin_lock(&ei->i_fc_lock);
 
 	return 0;
 }
@@ -611,10 +611,8 @@ static int __track_range(struct inode *inode, void *arg, bool update)
 	struct __track_range_args *__arg =
 		(struct __track_range_args *)arg;
 
-	if (inode->i_ino < EXT4_FIRST_INO(inode->i_sb)) {
-		ext4_debug("Special inode %ld being modified\n", inode->i_ino);
+	if (inode->i_ino < EXT4_FIRST_INO(inode->i_sb))
 		return -ECANCELED;
-	}
 
 	oldstart = ei->i_fc_lblk_start;
 
@@ -906,15 +904,15 @@ static int ext4_fc_write_inode_data(struct inode *inode, u32 *crc)
 	struct ext4_extent *ex;
 	int ret;
 
-	mutex_lock(&ei->i_fc_lock);
+	spin_lock(&ei->i_fc_lock);
 	if (ei->i_fc_lblk_len == 0) {
-		mutex_unlock(&ei->i_fc_lock);
+		spin_unlock(&ei->i_fc_lock);
 		return 0;
 	}
 	old_blk_size = ei->i_fc_lblk_start;
 	new_blk_size = ei->i_fc_lblk_start + ei->i_fc_lblk_len - 1;
 	ei->i_fc_lblk_len = 0;
-	mutex_unlock(&ei->i_fc_lock);
+	spin_unlock(&ei->i_fc_lock);
 
 	cur_lblk_off = old_blk_size;
 	jbd_debug(1, "%s: will try writing %d to %d for inode %ld\n",
diff --git a/fs/ext4/super.c b/fs/ext4/super.c
index 845f2f8aee5f..307871359e23 100644
--- a/fs/ext4/super.c
+++ b/fs/ext4/super.c
@@ -1354,7 +1354,7 @@ static struct inode *ext4_alloc_inode(struct super_block *sb)
 	atomic_set(&ei->i_unwritten, 0);
 	INIT_WORK(&ei->i_rsv_conversion_work, ext4_end_io_rsv_work);
 	ext4_fc_init_inode(&ei->vfs_inode);
-	mutex_init(&ei->i_fc_lock);
+	spin_lock_init(&ei->i_fc_lock);
 	return &ei->vfs_inode;
 }
 
-- 
2.37.0.170.g444d1eabd0-goog