[Cluster-devel] [PATCH v2] GFS2: Use rht_for_each_entry_rcu in glock_hash_walk

[Steven Whitehouse <swhiteho@redhat.com>]

Hi,

Looks good...

Acked-by: Steven Whitehouse <swhiteho@redhat.com>

Steve.

On 13/11/15 12:16, Andrew Price wrote:
> This lockdep splat was being triggered on umount:
>
> [55715.973122] ===============================
> [55715.980169] [ INFO: suspicious RCU usage. ]
> [55715.981021] 4.3.0-11553-g8d3de01-dirty #15 Tainted: G        W
> [55715.982353] -------------------------------
> [55715.983301] fs/gfs2/glock.c:1427 suspicious rcu_dereference_protected() usage!
>
> The code it refers to is the rht_for_each_entry_safe usage in
> glock_hash_walk. The condition that triggers the warning is
> lockdep_rht_bucket_is_held(tbl, hash) which is checked in the
> __rcu_dereference_protected macro.
>
> The rhashtable buckets are not changed in glock_hash_walk so it's safe
> to rely on the rcu protection. Replace the rht_for_each_entry_safe()
> usage with rht_for_each_entry_rcu(), which doesn't care whether the
> bucket lock is held if the rcu read lock is held.
>
> Signed-off-by: Andrew Price <anprice@redhat.com>
> ---
>   fs/gfs2/glock.c | 4 ++--
>   1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/fs/gfs2/glock.c b/fs/gfs2/glock.c
> index 32e7471..430326e 100644
> --- a/fs/gfs2/glock.c
> +++ b/fs/gfs2/glock.c
> @@ -1417,14 +1417,14 @@ static struct shrinker glock_shrinker = {
>   static void glock_hash_walk(glock_examiner examiner, const struct gfs2_sbd *sdp)
>   {
>   	struct gfs2_glock *gl;
> -	struct rhash_head *pos, *next;
> +	struct rhash_head *pos;
>   	const struct bucket_table *tbl;
>   	int i;
>   
>   	rcu_read_lock();
>   	tbl = rht_dereference_rcu(gl_hash_table.tbl, &gl_hash_table);
>   	for (i = 0; i < tbl->size; i++) {
> -		rht_for_each_entry_safe(gl, pos, next, tbl, i, gl_node) {
> +		rht_for_each_entry_rcu(gl, pos, tbl, i, gl_node) {
>   			if ((gl->gl_name.ln_sbd == sdp) &&
>   			    lockref_get_not_dead(&gl->gl_lockref))
>   				examiner(gl);