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Date:   Tue, 8 Mar 2022 13:03:44 +0100
From:   Jan Kara <jack@suse.cz>
To:     Harshad Shirwadkar <harshadshirwadkar@gmail.com>
Cc:     linux-ext4@vger.kernel.org, riteshh@linux.ibm.com, jack@suse.cz,
        tytso@mit.edu
Subject: Re: [PATCH 1/5] ext4: convert i_fc_lock to spinlock
Message-ID: <20220308120344.dplfoodvjl63u7jp@quack3.lan>
References: <20220308105112.404498-1-harshads@google.com>
 <20220308105112.404498-2-harshads@google.com>
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On Tue 08-03-22 02:51:08, Harshad Shirwadkar wrote:
> From: Harshad Shirwadkar <harshadshirwadkar@gmail.com>
> 
> Convert ext4_inode_info->i_fc_lock to spinlock to avoid sleeping
> in invalid contexts.
> 
> Signed-off-by: Harshad Shirwadkar <harshadshirwadkar@gmail.com>

I don't think ext4_debug() is safe under spinlock in __track_range(). But
otherwise the patch looks good to me. So feel free to add:

Reviewed-by: Jan Kara <jack@suse.cz>

after fixing this.

								Honza

> ---
>  fs/ext4/ext4.h        |  7 +++++--
>  fs/ext4/fast_commit.c | 24 ++++++++++++++----------
>  fs/ext4/super.c       |  2 +-
>  3 files changed, 20 insertions(+), 13 deletions(-)
> 
> diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h
> index 3f87cca49f0c..fb6d65f1176f 100644
> --- a/fs/ext4/ext4.h
> +++ b/fs/ext4/ext4.h
> @@ -1065,8 +1065,11 @@ 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 5ac594e03402..4f2caf6f987c 100644
> --- a/fs/ext4/fast_commit.c
> +++ b/fs/ext4/fast_commit.c
> @@ -387,7 +387,7 @@ static int ext4_fc_track_template(
>  		return -EINVAL;
>  
>  	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 {
> @@ -395,7 +395,7 @@ 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;
> @@ -427,11 +427,11 @@ 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;
>  	}
>  
> @@ -444,7 +444,7 @@ 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,
> @@ -478,7 +478,7 @@ 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;
>  }
> @@ -867,15 +867,15 @@ 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",
> @@ -972,9 +972,13 @@ static int ext4_fc_wait_inode_data_all(journal_t *journal)
>  
>  	spin_lock(&sbi->s_fc_lock);
>  	list_for_each_entry_safe(pos, n, &sbi->s_fc_q[FC_Q_MAIN], i_fc_list) {
> +		spin_lock(&pos->i_fc_lock);
>  		if (!ext4_test_inode_state(&pos->vfs_inode,
> -					   EXT4_STATE_FC_COMMITTING))
> +					   EXT4_STATE_FC_COMMITTING)) {
> +			spin_unlock(&pos->i_fc_lock);
>  			continue;
> +		}
> +		spin_unlock(&pos->i_fc_lock);
>  		spin_unlock(&sbi->s_fc_lock);
>  
>  		ret = jbd2_wait_inode_data(journal, pos->jinode);
> diff --git a/fs/ext4/super.c b/fs/ext4/super.c
> index 1e5f4994fe57..38d63113c383 100644
> --- a/fs/ext4/super.c
> +++ b/fs/ext4/super.c
> @@ -1346,7 +1346,7 @@ 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;
>  }
>  
> -- 
> 2.35.1.616.g0bdcbb4464-goog
> 
-- 
Jan Kara <jack@suse.com>
SUSE Labs, CR