linux-kernel - Re: [RFC PATCH 5/6] ext4: Search for an inode to update under the RCU lock if we can

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Message-ID: <20190418150833.GE2217@ZenIV.linux.org.uk>
Date:   Thu, 18 Apr 2019 16:08:34 +0100
From:   Al Viro <viro@...iv.linux.org.uk>
To:     David Howells <dhowells@...hat.com>
Cc:     Theodore Ts'o <tytso@....edu>,
        Andreas Dilger <adilger.kernel@...ger.ca>,
        linux-ext4@...r.kernel.org, linux-afs@...ts.infradead.org,
        linux-ntfs-dev@...ts.sourceforge.net,
        linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH 5/6] ext4: Search for an inode to update under the
 RCU lock if we can

On Thu, Apr 18, 2019 at 03:06:44PM +0100, David Howells wrote:
> +	inode = find_inode_by_ino_rcu(sb, ino);
> +	if (!inode)
> +		return;
>  
>  	if ((inode->i_ino != ino) ||
>  	    (inode->i_state & (I_FREEING | I_WILL_FREE | I_NEW |
>  			       I_DIRTY_INODE)) ||
>  	    ((inode->i_state & I_DIRTY_TIME) == 0))

Umm...  The situation with memory barriers here needs to be documented,
IMO.  And I'm not sure if the thing is actually correct...