linux-kernel - Re: [RESEND PATCH] drivers/md: Use rcu_dereference() for accessing rcu pointer

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Date:	Sun, 28 Sep 2014 14:43:25 -0700
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	Pranith Kumar <bobby.prani@...il.com>
Cc:	Alasdair Kergon <agk@...hat.com>,
	Mike Snitzer <snitzer@...hat.com>,
	"maintainer:DEVICE-MAPPER (LVM)" <dm-devel@...hat.com>,
	Neil Brown <neilb@...e.de>, linux-raid@...r.kernel.org,
	open list <linux-kernel@...r.kernel.org>
Subject: Re: [RESEND PATCH] drivers/md: Use rcu_dereference() for accessing
 rcu pointer

On Sun, Sep 28, 2014 at 11:05:04AM -0400, Pranith Kumar wrote:
> Got Paul's email wrong the first time.
> 
> The map field in 'struct mapped_device' is an rcu pointer. Use rcu_dereference()
> while accessing it.
> 
> Signed-off-by: Pranith Kumar <bobby.prani@...il.com>

OK, I now have all three queued (including the extraneous first line of
the commit log above...), will see what 0day thinks of it.

							Thanx, Paul

> ---
>  drivers/md/dm.c | 8 ++++----
>  1 file changed, 4 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/md/dm.c b/drivers/md/dm.c
> index 746411b..fbdf0bb 100644
> --- a/drivers/md/dm.c
> +++ b/drivers/md/dm.c
> @@ -2211,7 +2211,7 @@ static struct dm_table *__bind(struct mapped_device *md, struct dm_table *t,
> 
>  	merge_is_optional = dm_table_merge_is_optional(t);
> 
> -	old_map = md->map;
> +	old_map = rcu_dereference(md->map);
>  	rcu_assign_pointer(md->map, t);
>  	md->immutable_target_type = dm_table_get_immutable_target_type(t);
> 
> @@ -2230,7 +2230,7 @@ static struct dm_table *__bind(struct mapped_device *md, struct dm_table *t,
>   */
>  static struct dm_table *__unbind(struct mapped_device *md)
>  {
> -	struct dm_table *map = md->map;
> +	struct dm_table *map = rcu_dereference(md->map);
> 
>  	if (!map)
>  		return NULL;
> @@ -2624,7 +2624,7 @@ int dm_suspend(struct mapped_device *md, unsigned suspend_flags)
>  		goto out_unlock;
>  	}
> 
> -	map = md->map;
> +	map = rcu_dereference(md->map);
> 
>  	/*
>  	 * DMF_NOFLUSH_SUSPENDING must be set before presuspend.
> @@ -2718,7 +2718,7 @@ int dm_resume(struct mapped_device *md)
>  	if (!dm_suspended_md(md))
>  		goto out;
> 
> -	map = md->map;
> +	map = rcu_dereference(md->map);
>  	if (!map || !dm_table_get_size(map))
>  		goto out;
> 
> -- 
> 1.9.1
> 

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