linux-kernel - Re: [PATCH] fs: Safe rcu access to hlist.

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Message-ID: <20171120185535.ggmnui2ud3ixqw7g@debian>
Date:   Mon, 20 Nov 2017 13:55:35 -0500
From:   Tim Hansen <devtimhansen@...il.com>
To:     Al Viro <viro@...IV.linux.org.uk>
Cc:     linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        alexander.levin@....verizon.com
Subject: Re: [PATCH] fs: Safe rcu access to hlist.

On Sun, Nov 19, 2017 at 09:28:49PM +0000, Al Viro wrote:
> On Sun, Nov 19, 2017 at 03:02:10PM -0500, Tim Hansen wrote:
> > Adds hlist_first_rcu and hlist_next_rcu for safe access
> > to the hlist in seq_hlist_next_rcu.
> > 
> > Found on linux-next branch, tag next-20171117 with sparse.
> 
> Frankly, I'm tempted to take sparse RCU annotations out for good -
> they are far too noisy and I'm not sure sparse is suitable for the
> analysis needed to prove safety of that stuff, so unless you (or
> somebody else) figures out how to use them in a reasonably clean
> way, we'd probably be better off just dropping them.

Can you detail how sparse is insufficent to prove RCU saftey? 
I'm not an RCU expert by any means but I don't know of any 
complaints regarding the capabilities of sparse to detect RCU
correctness in the community.  That however could just be my 
own ignornace. As far as I know these sparse RCU annotations 
are used widely across other subsystems.

I'd defer to other people more knowledgable on sparse to chime 
in regarding the "correctness" of it's capability on the RCU.