linux-kernel - Re: [PATCH 1/3] kernfs: Introduce separate rwsem to protect inode attributes.

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Date:   Thu, 2 Mar 2023 16:14:04 +0000
From:   Matthew Wilcox <willy@...radead.org>
To:     Imran Khan <imran.f.khan@...cle.com>
Cc:     tj@...nel.org, gregkh@...uxfoundation.org, viro@...iv.linux.org.uk,
        linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        joe.jin@...cle.com
Subject: Re: [PATCH 1/3] kernfs: Introduce separate rwsem to protect inode
 attributes.

On Thu, Mar 02, 2023 at 03:32:01PM +1100, Imran Khan wrote:
> +++ b/fs/kernfs/kernfs-internal.h
> @@ -47,6 +47,7 @@ struct kernfs_root {
>  
>  	wait_queue_head_t	deactivate_waitq;
>  	struct rw_semaphore	kernfs_rwsem;
> +	struct rw_semaphore	kernfs_iattr_rwsem;
>  };
>  
>  /* +1 to avoid triggering overflow warning when negating it */

Can you explain why we want one iattr rwsem per kernfs_root instead of
one rwsem per kernfs_node?