linux-kernel - Re: [Xen-devel] [PATCH 2/2] xen-blkfront: implement safe version of llist_for_each

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Message-ID: <20121207202003.GA9462@phenom.dumpdata.com>
Date:	Fri, 7 Dec 2012 15:20:03 -0500
From:	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
To:	Roger Pau Monne <roger.pau@...rix.com>, akpm@...ux-foundation.org,
	sfr@...b.auug.org.au, peterz@...radead.org
Cc:	linux-kernel@...r.kernel.org,
	Konrad Rzeszutek Wilk <konrad@...nel.org>,
	xen-devel@...ts.xen.org
Subject: Re: [Xen-devel] [PATCH 2/2] xen-blkfront: implement safe version of
 llist_for_each_entry

On Tue, Dec 04, 2012 at 03:21:53PM +0100, Roger Pau Monne wrote:
> Implement a safe version of llist_for_each_entry, and use it in
> blkif_free. Previously grants where freed while iterating the list,
> which lead to dereferences when trying to fetch the next item.

Looks like xen-blkfront is the only user of this llist_for_each_entry.

Would it be more prudent to put the macro in the llist.h file?

> 
> Reported-by: Dan Carpenter <dan.carpenter@...cle.com>
> Signed-off-by: Roger Pau Monné <roger.pau@...rix.com>
> Cc: Konrad Rzeszutek Wilk <konrad@...nel.org>
> Cc: xen-devel@...ts.xen.org
> ---
>  drivers/block/xen-blkfront.c |   10 +++++++++-
>  1 files changed, 9 insertions(+), 1 deletions(-)
> 
> diff --git a/drivers/block/xen-blkfront.c b/drivers/block/xen-blkfront.c
> index 96e9b00..df21b05 100644
> --- a/drivers/block/xen-blkfront.c
> +++ b/drivers/block/xen-blkfront.c
> @@ -143,6 +143,13 @@ static DEFINE_SPINLOCK(minor_lock);
>  
>  #define DEV_NAME	"xvd"	/* name in /dev */
>  
> +#define llist_for_each_entry_safe(pos, n, node, member)		\
> +	for ((pos) = llist_entry((node), typeof(*(pos)), member),	\
> +	     (n) = (pos)->member.next;					\
> +	     &(pos)->member != NULL;					\
> +	     (pos) = llist_entry(n, typeof(*(pos)), member),		\
> +	     (n) = (&(pos)->member != NULL) ? (pos)->member.next : NULL)
> +
>  static int get_id_from_freelist(struct blkfront_info *info)
>  {
>  	unsigned long free = info->shadow_free;
> @@ -792,6 +799,7 @@ static void blkif_free(struct blkfront_info *info, int suspend)
>  {
>  	struct llist_node *all_gnts;
>  	struct grant *persistent_gnt;
> +	struct llist_node *n;
>  
>  	/* Prevent new requests being issued until we fix things up. */
>  	spin_lock_irq(&info->io_lock);
> @@ -804,7 +812,7 @@ static void blkif_free(struct blkfront_info *info, int suspend)
>  	/* Remove all persistent grants */
>  	if (info->persistent_gnts_c) {
>  		all_gnts = llist_del_all(&info->persistent_gnts);
> -		llist_for_each_entry(persistent_gnt, all_gnts, node) {
> +		llist_for_each_entry_safe(persistent_gnt, n, all_gnts, node) {
>  			gnttab_end_foreign_access(persistent_gnt->gref, 0, 0UL);
>  			__free_page(pfn_to_page(persistent_gnt->pfn));
>  			kfree(persistent_gnt);
> -- 
> 1.7.7.5 (Apple Git-26)
> 
> 
> _______________________________________________
> Xen-devel mailing list
> Xen-devel@...ts.xen.org
> http://lists.xen.org/xen-devel
> 
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