perf cgroup: Convert cgroup_sel.refcnt from atomic_t to refcount_t

The refcount_t type and corresponding API should be used instead of
atomic_t when the variable is used as a reference counter.

This allows to avoid accidental refcounter overflows that might lead to
use-after-free situations.

Signed-off-by: Elena Reshetova <[e-mail]>
Signed-off-by: David Windsor <[e-mail]>
Signed-off-by: Hans Liljestrand <[e-mail]>
Signed-off-by: Kees Kook <[e-mail]>
Tested-by: Arnaldo Carvalho de Melo <[e-mail]>
Cc: Alexander Shishkin <[e-mail]>
Cc: [e-mail]
Cc: Andrew Morton <[e-mail]>
Cc: David Windsor <[e-mail]>
Cc: Greg Kroah-Hartman <[e-mail]>
Cc: Hans Liljestrand <[e-mail]>
Cc: Jiri Olsa <[e-mail]>
Cc: Kees Kook <[e-mail]>
Cc: Mark Rutland <[e-mail]>
Cc: Matija Glavinic Pecotic <[e-mail]>
Cc: Peter Zijlstra <[e-mail]>
Link: http://lkml.kernel.org/r/[e-mail]
Signed-off-by: Arnaldo Carvalho de Melo <[e-mail]>

tools/perf/util/cgroup.c

···
 			goto found;
 		n++;
 	}
-	if (atomic_read(&cgrp->refcnt) == 0)
+	if (refcount_read(&cgrp->refcnt) == 0)
 		free(cgrp);
 
 	return -1;
 found:
-	atomic_inc(&cgrp->refcnt);
+	refcount_inc(&cgrp->refcnt);
 	counter->cgrp = cgrp;
 	return 0;
 }
 
 void close_cgroup(struct cgroup_sel *cgrp)
 {
-	if (cgrp && atomic_dec_and_test(&cgrp->refcnt)) {
+	if (cgrp && refcount_dec_and_test(&cgrp->refcnt)) {
 		close(cgrp->fd);
 		zfree(&cgrp->name);
 		free(cgrp);

tools/perf/util/cgroup.h

···
 #ifndef __CGROUP_H__
 #define __CGROUP_H__
 
-#include <linux/atomic.h>
+#include <linux/refcount.h>
 
 struct option;
 
 struct cgroup_sel {
 	char *name;
 	int fd;
-	atomic_t refcnt;
+	refcount_t refcnt;
 };