padata: Convert from atomic_t to refcount_t on parallel_data->refcnt

refcount_t type and corresponding API can protect refcounters from
accidental underflow and overflow and further use-after-free situations.
Signed-off-by: Xiyu Yang <xiyuyang19@fudan.edu.cn>
Signed-off-by: Xin Tan <tanxin.ctf@gmail.com>
Acked-by: Daniel Jordan <daniel.m.jordan@oracle.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

include/linux/padata.h

@@ -12,6 +12,7 @@
 #ifndef PADATA_H
 #define PADATA_H
 
+#include <linux/refcount.h>
 #include <linux/compiler_types.h>
 #include <linux/workqueue.h>
 #include <linux/spinlock.h>
@@ -96,7 +97,7 @@ struct parallel_data {
 	struct padata_shell		*ps;
 	struct padata_list		__percpu *reorder_list;
 	struct padata_serial_queue	__percpu *squeue;
-	atomic_t			refcnt;
+	refcount_t			refcnt;
 	unsigned int			seq_nr;
 	unsigned int			processed;
 	int				cpu;

kernel/padata.c

@@ -211,7 +211,7 @@ int padata_do_parallel(struct padata_shell *ps,
 	if ((pinst->flags & PADATA_RESET))
 		goto out;
 
-	atomic_inc(&pd->refcnt);
+	refcount_inc(&pd->refcnt);
 	padata->pd = pd;
 	padata->cb_cpu = *cb_cpu;
 
@@ -383,7 +383,7 @@ static void padata_serial_worker(struct work_struct *serial_work)
 	}
 	local_bh_enable();
 
-	if (atomic_sub_and_test(cnt, &pd->refcnt))
+	if (refcount_sub_and_test(cnt, &pd->refcnt))
 		padata_free_pd(pd);
 }
 
@@ -593,7 +593,7 @@ static struct parallel_data *padata_alloc_pd(struct padata_shell *ps)
 	padata_init_reorder_list(pd);
 	padata_init_squeues(pd);
 	pd->seq_nr = -1;
-	atomic_set(&pd->refcnt, 1);
+	refcount_set(&pd->refcnt, 1);
 	spin_lock_init(&pd->lock);
 	pd->cpu = cpumask_first(pd->cpumask.pcpu);
 	INIT_WORK(&pd->reorder_work, invoke_padata_reorder);
@@ -667,7 +667,7 @@ static int padata_replace(struct padata_instance *pinst)
 	synchronize_rcu();
 
 	list_for_each_entry_continue_reverse(ps, &pinst->pslist, list)
-		if (atomic_dec_and_test(&ps->opd->refcnt))
+		if (refcount_dec_and_test(&ps->opd->refcnt))
 			padata_free_pd(ps->opd);
 
 	pinst->flags &= ~PADATA_RESET;