linux-ext4 - Re: [PATCH v2 26/54] fs: use igrab in insert_inode

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Message-ID: <20250828-wohngebiet-pfahl-a6f23062f6e1@brauner>
Date: Thu, 28 Aug 2025 14:15:46 +0200
From: Christian Brauner <brauner@...nel.org>
To: Josef Bacik <josef@...icpanda.com>
Cc: linux-fsdevel@...r.kernel.org, linux-btrfs@...r.kernel.org, 
	kernel-team@...com, linux-ext4@...r.kernel.org, linux-xfs@...r.kernel.org, 
	viro@...iv.linux.org.uk, amir73il@...il.com
Subject: Re: [PATCH v2 26/54] fs: use igrab in insert_inode_locked

On Tue, Aug 26, 2025 at 11:39:26AM -0400, Josef Bacik wrote:
> Follow the same pattern in find_inode*. Instead of checking for
> I_WILL_FREE|I_FREEING simply call igrab() and if it succeeds we're done.
> 
> Signed-off-by: Josef Bacik <josef@...icpanda.com>
> ---
>  fs/inode.c | 8 +++-----
>  1 file changed, 3 insertions(+), 5 deletions(-)
> 
> diff --git a/fs/inode.c b/fs/inode.c
> index 8ae9ed9605ef..d34da95a3295 100644
> --- a/fs/inode.c
> +++ b/fs/inode.c
> @@ -1883,11 +1883,8 @@ int insert_inode_locked(struct inode *inode)
>  				continue;
>  			if (old->i_sb != sb)
>  				continue;
> -			spin_lock(&old->i_lock);
> -			if (old->i_state & (I_FREEING|I_WILL_FREE)) {
> -				spin_unlock(&old->i_lock);
> +			if (!igrab(old))
>  				continue;
> -			}
>  			break;
>  		}
>  		if (likely(!old)) {
> @@ -1899,12 +1896,13 @@ int insert_inode_locked(struct inode *inode)
>  			spin_unlock(&inode_hash_lock);
>  			return 0;
>  		}
> +		spin_lock(&old->i_lock);
>  		if (unlikely(old->i_state & I_CREATING)) {
>  			spin_unlock(&old->i_lock);
>  			spin_unlock(&inode_hash_lock);
> +			iput(old);
>  			return -EBUSY;
>  		}
> -		__iget(old);
>  		spin_unlock(&old->i_lock);
>  		spin_unlock(&inode_hash_lock);
>  		wait_on_inode(old);
> -- 
> 2.49.0
> 

So looking at the function in full context:

int insert_inode_locked(struct inode *inode)
{
	struct super_block *sb = inode->i_sb;
	ino_t ino = inode->i_ino;
	struct hlist_head *head = inode_hashtable + hash(sb, ino);

	while (1) {
		struct inode *old = NULL;
		spin_lock(&inode_hash_lock);
		hlist_for_each_entry(old, head, i_hash) {
			if (old->i_ino != ino)
				continue;
			if (old->i_sb != sb)
				continue;
			if (!igrab(old))
				continue;
			break;
		}
		if (likely(!old)) {
			spin_lock(&inode->i_lock);
			iobj_get(inode);

Sorry, this is probably me being confused.
Say we allocated a new inode then we've definitely went through
inode_init_always() and so i_obj_count == i_count == 1.
Then we insert it into the hash table. For that we only take an
i_obj_count but no i_count bringing it to 2.

So for the hashlist we only deal with i_obj_count.

Is that documented somewhere? I probably just read over it.