[PATCH] mm: zcache: zcache_cleancache_flush_fs fix

[PATCH] mm: zcache: zcache_cleancache_flush_fs fix

[Piotr Sarna]

This patch fixes "mm: zcache: core functions added" patch,
available at https://lkml.org/lkml/2013/7/20/90.
It regards incorrect implementation of zcache_cleancache_flush_fs().

Function above should be effective only if cleancache pool referred
by pool_id is valid. This issue is checked by testing whether zpool
points to NULL.

Unfortunately, if filesystem mount fails, such pool is never created
and fs/super.c calls cleancache_invalidate_fs() function with pool_id
parameter set to -1. This results in assigning zpool with pools[-1],
which causes zpool to be not NULL and thus whole function hangs on
uninitialized read-write lock.

To prevent that behaviour, pool_id should be checked for being positive
before assigning zpool variable with pools[pool_id].

Signed-off-by: Piotr Sarna <p.sarna@partner.samsung.com>
Acked-by: Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>
Signed-off-by: Kyungmin Park <kyungmin.park@samsung.com>
---
 mm/zcache.c |    6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/mm/zcache.c b/mm/zcache.c
index a2408e8..7e6d2e7 100644
--- a/mm/zcache.c
+++ b/mm/zcache.c
@@ -600,8 +600,12 @@ static void zcache_cleancache_flush_fs(int pool_id)
 	struct zcache_rb_entry *entry = NULL;
 	struct rb_node *node;
 	unsigned long flags1, flags2;
-	struct zcache_pool *zpool = zcache.pools[pool_id];
+	struct zcache_pool *zpool;
+
+	if (pool_id < 0)
+		return;
 
+	zpool = zcache.pools[pool_id];
 	if (!zpool)
 		return;
 
-- 
1.7.9.5

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Re: [PATCH] mm: zcache: zcache_cleancache_flush_fs fix

[Bob Liu]

Hi Piotr,

On 08/06/2013 05:36 PM, Piotr Sarna wrote:
> This patch fixes "mm: zcache: core functions added" patch,
> available at https://lkml.org/lkml/2013/7/20/90.
> It regards incorrect implementation of zcache_cleancache_flush_fs().
> 
> Function above should be effective only if cleancache pool referred
> by pool_id is valid. This issue is checked by testing whether zpool
> points to NULL.
> 
> Unfortunately, if filesystem mount fails, such pool is never created
> and fs/super.c calls cleancache_invalidate_fs() function with pool_id
> parameter set to -1. This results in assigning zpool with pools[-1],
> which causes zpool to be not NULL and thus whole function hangs on
> uninitialized read-write lock.
> 
> To prevent that behaviour, pool_id should be checked for being positive
> before assigning zpool variable with pools[pool_id].
> 
> Signed-off-by: Piotr Sarna <p.sarna@partner.samsung.com>
> Acked-by: Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>
> Signed-off-by: Kyungmin Park <kyungmin.park@samsung.com>

Yes, that's a problem. Thank you very much!
I'm so glad you are also interesting in zcache. I'm preparing a update
version of zcache which is still under testing currently.

> ---
>  mm/zcache.c |    6 +++++-
>  1 file changed, 5 insertions(+), 1 deletion(-)
> 
> diff --git a/mm/zcache.c b/mm/zcache.c
> index a2408e8..7e6d2e7 100644
> --- a/mm/zcache.c
> +++ b/mm/zcache.c
> @@ -600,8 +600,12 @@ static void zcache_cleancache_flush_fs(int pool_id)
>  	struct zcache_rb_entry *entry = NULL;
>  	struct rb_node *node;
>  	unsigned long flags1, flags2;
> -	struct zcache_pool *zpool = zcache.pools[pool_id];
> +	struct zcache_pool *zpool;
> +
> +	if (pool_id < 0)
> +		return;
>  
> +	zpool = zcache.pools[pool_id];
>  	if (!zpool)
>  		return;
>  
> 

-- 
Regards,
-Bob

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