Fix coverity defects: CID 150924

CID 150924: Unchecked return value (CHECKED_RETURN)
- On taskq_dispatch failure the reference must be dropped and
  this entry can be safely skipped.  This case should be impossible
  in the existing implementation but should be handled regardless.
  
Reviewed-by: Brian Behlendorf <[email protected]>
Signed-off-by: luozhengzheng <[email protected]>
Closes #5278 

1 files changed, 5 insertions, 1 deletions

diff --git a/module/zfs/arc.c b/module/zfs/arc.c
index 7bae2c42d..0c5e66cbe 100644
--- a/module/zfs/arc.c
+++ b/module/zfs/arc.c
@@ -3472,7 +3472,11 @@ arc_prune_async(int64_t adjust)
 
 		refcount_add(&ap->p_refcnt, ap->p_pfunc);
 		ap->p_adjust = adjust;
-		taskq_dispatch(arc_prune_taskq, arc_prune_task, ap, TQ_SLEEP);
+		if (taskq_dispatch(arc_prune_taskq, arc_prune_task,
+		    ap, TQ_SLEEP) == 0) {
+			refcount_remove(&ap->p_refcnt, ap->p_pfunc);
+			continue;
+		}
 		ARCSTAT_BUMP(arcstat_prune);
 	}
 	mutex_exit(&arc_prune_mtx);