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Date:   Tue, 15 Dec 2020 12:24:47 +0000
From:   Matthew Wilcox <willy@infradead.org>
To:     Jens Axboe <axboe@kernel.dk>
Cc:     linux-fsdevel@vger.kernel.org, torvalds@linux-foundation.org,
        viro@zeniv.linux.org.uk
Subject: Re: [PATCH 2/4] fs: add support for LOOKUP_NONBLOCK
Message-ID: <20201215122447.GQ2443@casper.infradead.org>
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 <20201214191323.173773-3-axboe@kernel.dk>
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On Mon, Dec 14, 2020 at 12:13:22PM -0700, Jens Axboe wrote:
> +++ b/fs/namei.c
> @@ -686,6 +686,8 @@ static bool try_to_unlazy(struct nameidata *nd)
>  	BUG_ON(!(nd->flags & LOOKUP_RCU));
>  
>  	nd->flags &= ~LOOKUP_RCU;
> +	if (nd->flags & LOOKUP_NONBLOCK)
> +		goto out1;

If we try a walk in a non-blocking context, it fails, then we punt to
a thread, do we want to prohibit that thread trying an RCU walk first?
I can see arguments both ways -- this may only be a temporary RCU walk
failure, or we may never be able to RCU walk this path.