[PATCH] 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.

Reviewed-by: Jan Kara <jack@xxxxxxx>
Signed-off-by: Harshad Shirwadkar <harshadshirwadkar@xxxxxxxxx>
---
 fs/ext4/ext4.h        |  7 +++++--
 fs/ext4/fast_commit.c | 24 +++++++++++-------------
 fs/ext4/super.c       |  2 +-
 3 files changed, 17 insertions(+), 16 deletions(-)

diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h
index 08acd1522..51ae1785a 100644
--- a/fs/ext4/ext4.h
+++ b/fs/ext4/ext4.h
@@ -1062,8 +1062,11 @@ 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 3926a05ec..8731728cc 100644
--- a/fs/ext4/fast_commit.c
+++ b/fs/ext4/fast_commit.c
@@ -382,7 +382,7 @@ 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 {
@@ -390,7 +390,7 @@ 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;
@@ -424,19 +424,19 @@ static int __track_dentry_update(struct inode *inode, void *arg, bool update)
 	struct super_block *sb = inode->i_sb;
 	struct ext4_sb_info *sbi = EXT4_SB(sb);
 
-	mutex_unlock(&ei->i_fc_lock);
+	spin_unlock(&ei->i_fc_lock);
 
 	if (IS_ENCRYPTED(dir)) {
 		ext4_fc_mark_ineligible(sb, EXT4_FC_REASON_ENCRYPTED_FILENAME,
 					NULL);
-		mutex_lock(&ei->i_fc_lock);
+		spin_lock(&ei->i_fc_lock);
 		return -EOPNOTSUPP;
 	}
 
 	node = kmem_cache_alloc(ext4_fc_dentry_cachep, GFP_NOFS);
 	if (!node) {
 		ext4_fc_mark_ineligible(sb, EXT4_FC_REASON_NOMEM, NULL);
-		mutex_lock(&ei->i_fc_lock);
+		spin_lock(&ei->i_fc_lock);
 		return -ENOMEM;
 	}
 
@@ -448,7 +448,7 @@ static int __track_dentry_update(struct inode *inode, void *arg, bool update)
 		if (!node->fcd_name.name) {
 			kmem_cache_free(ext4_fc_dentry_cachep, node);
 			ext4_fc_mark_ineligible(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,
@@ -482,7 +482,7 @@ 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;
 }
@@ -614,10 +614,8 @@ 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;
 
@@ -902,15 +900,15 @@ 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;
 	ext4_debug("will try writing %d to %d for inode %ld\n",
diff --git a/fs/ext4/super.c b/fs/ext4/super.c
index e72145c4a..d37944839 100644
--- a/fs/ext4/super.c
+++ b/fs/ext4/super.c
@@ -1423,7 +1423,7 @@ 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;
 }
 
-- 
2.46.0.184.g6999bdac58-goog