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Date:   Wed, 16 Dec 2020 02:43:15 +0000
From:   Al Viro <viro@zeniv.linux.org.uk>
To:     Jens Axboe <axboe@kernel.dk>
Cc:     linux-fsdevel@vger.kernel.org, torvalds@linux-foundation.org
Subject: Re: [PATCH 2/4] fs: add support for LOOKUP_NONBLOCK
Message-ID: <20201216024315.GJ3579531@ZenIV.linux.org.uk>
References: <20201214191323.173773-1-axboe@kernel.dk>
 <20201214191323.173773-3-axboe@kernel.dk>
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On Mon, Dec 14, 2020 at 12:13:22PM -0700, Jens Axboe wrote:
> @@ -3140,6 +3149,12 @@ static const char *open_last_lookups(struct nameidata *nd,
>  			return ERR_CAST(dentry);
>  		if (likely(dentry))
>  			goto finish_lookup;
> +		/*
> +		 * We can't guarantee nonblocking semantics beyond this, if
> +		 * the fast lookup fails.
> +		 */
> +		if (nd->flags & LOOKUP_NONBLOCK)
> +			return ERR_PTR(-EAGAIN);
>  
>  		BUG_ON(nd->flags & LOOKUP_RCU);

That can't be right - we already must have removed LOOKUP_RCU here
(see BUG_ON() right after that point).  What is that test supposed
to catch?

What am I missing here?