linux-kernel - Re: [PATCH 3/3] btrfs: refactor btrfs

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Date:	Sun, 30 Nov 2014 10:26:43 -0500
From:	Pranith Kumar <bobby.prani@...il.com>
To:	Omar Sandoval <osandov@...ndov.com>
Cc:	Chris Mason <clm@...com>, Josef Bacik <jbacik@...com>,
	Joe Perches <joe@...ches.com>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Josh Triplett <josh@...htriplett.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
	LKML <linux-kernel@...r.kernel.org>, linux-btrfs@...r.kernel.org
Subject: Re: [PATCH 3/3] btrfs: refactor btrfs_device->name updates

On Sun, Nov 30, 2014 at 3:26 AM, Omar Sandoval <osandov@...ndov.com> wrote:
> The rcu_string API introduced some new sparse errors but also revealed existing
> ones. First of all, the name in struct btrfs_device should be annotated as
> __rcu to prevent unsafe reads. Additionally, updates should go through
> rcu_dereference_protected to make it clear what's going on. This introduces
> some helper functions that factor out this functionality.
>
> Signed-off-by: Omar Sandoval <osandov@...ndov.com>
> diff --git a/fs/btrfs/volumes.h b/fs/btrfs/volumes.h
> index 6e04f27..2298a70 100644
> --- a/fs/btrfs/volumes.h
> +++ b/fs/btrfs/volumes.h
> @@ -54,7 +54,7 @@ struct btrfs_device {
>
>         struct btrfs_root *dev_root;
>
> -       struct rcu_string *name;
> +       struct rcu_string __rcu *name;
>
>         u64 generation;
>

Since rcu_strings are rcu specific, why not annotate the char pointer
in 'struct rcu_string' with __rcu annotation? That should catch all
error-prone users of rcu_string.

-- 
Pranith
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