[Cluster-devel] [PATCH] gfs2: Add missing rcu locking for glock lookup

[Steven Whitehouse <swhiteho@redhat.com>]

Hi,

Looks good, but can we fix that "retry for 100 times" loop too at the 
same time? There does appear to be an rhashtable API function that does 
what we need there,

Steve.

On 22/02/17 15:09, Andreas Gruenbacher wrote:
> From: Andrew Price <anprice@redhat.com>
>
> We must hold the rcu read lock across looking up glocks and trying to
> bump their refcount to prevent the glocks from being freed in between.
>
> Signed-off-by: Andreas Gruenbacher <agruenba@redhat.com>
> ---
>   fs/gfs2/glock.c | 5 +++++
>   1 file changed, 5 insertions(+)
>
> diff --git a/fs/gfs2/glock.c b/fs/gfs2/glock.c
> index 94f50ca..1d60f5f 100644
> --- a/fs/gfs2/glock.c
> +++ b/fs/gfs2/glock.c
> @@ -658,9 +658,11 @@ int gfs2_glock_get(struct gfs2_sbd *sdp, u64 number,
>   	struct kmem_cache *cachep;
>   	int ret, tries = 0;
>   
> +	rcu_read_lock();
>   	gl = rhashtable_lookup_fast(&gl_hash_table, &name, ht_parms);
>   	if (gl && !lockref_get_not_dead(&gl->gl_lockref))
>   		gl = NULL;
> +	rcu_read_unlock();
>   
>   	*glp = gl;
>   	if (gl)
> @@ -728,15 +730,18 @@ int gfs2_glock_get(struct gfs2_sbd *sdp, u64 number,
>   
>   	if (ret == -EEXIST) {
>   		ret = 0;
> +		rcu_read_lock();
>   		tmp = rhashtable_lookup_fast(&gl_hash_table, &name, ht_parms);
>   		if (tmp == NULL || !lockref_get_not_dead(&tmp->gl_lockref)) {
>   			if (++tries < 100) {
> +				rcu_read_unlock();
>   				cond_resched();
>   				goto again;
>   			}
>   			tmp = NULL;
>   			ret = -ENOMEM;
>   		}
> +		rcu_read_unlock();
>   	} else {
>   		WARN_ON_ONCE(ret);
>   	}