linux-kernel - [PATCH 12/35] perf comm: Convert comm_str.refcnt from atomic_t to refcount

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Message-Id: <20170306193825.24011-13-acme@kernel.org>
Date:   Mon,  6 Mar 2017 16:38:02 -0300
From:   Arnaldo Carvalho de Melo <acme@...nel.org>
To:     Ingo Molnar <mingo@...nel.org>
Cc:     linux-kernel@...r.kernel.org,
        Elena Reshetova <elena.reshetova@...el.com>,
        David Windsor <dwindsor@...il.com>,
        Hans Liljestrand <ishkamiel@...il.com>,
        Kees Kook <keescook@...omium.org>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Jiri Olsa <jolsa@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Matija Glavinic Pecotic <matija.glavinic-pecotic.ext@...ia.com>,
        Peter Zijlstra <peterz@...radead.org>,
        alsa-devel@...a-project.org,
        Arnaldo Carvalho de Melo <acme@...hat.com>
Subject: [PATCH 12/35] perf comm: Convert comm_str.refcnt from atomic_t to refcount_t

From: Elena Reshetova <elena.reshetova@...el.com>

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 <elena.reshetova@...el.com>
Signed-off-by: David Windsor <dwindsor@...il.com>
Signed-off-by: Hans Liljestrand <ishkamiel@...il.com>
Signed-off-by: Kees Kook <keescook@...omium.org>
Tested-by: Arnaldo Carvalho de Melo <acme@...hat.com>
Cc: Alexander Shishkin <alexander.shishkin@...ux.intel.com>
Cc: Andrew Morton <akpm@...ux-foundation.org>
Cc: David Windsor <dwindsor@...il.com>
Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc: Hans Liljestrand <ishkamiel@...il.com>
Cc: Jiri Olsa <jolsa@...nel.org>
Cc: Kees Kook <keescook@...omium.org>
Cc: Mark Rutland <mark.rutland@....com>
Cc: Matija Glavinic Pecotic <matija.glavinic-pecotic.ext@...ia.com>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: alsa-devel@...a-project.org
Link: http://lkml.kernel.org/r/1487691303-31858-4-git-send-email-elena.reshetova@intel.com
[ Reinstated comm_str__get() function, needed when reusing entries in the rbtree ]
Signed-off-by: Arnaldo Carvalho de Melo <acme@...hat.com>

Signed-off-by: Arnaldo Carvalho de Melo <acme@...hat.com>
---
 tools/perf/util/comm.c | 15 ++++++---------
 1 file changed, 6 insertions(+), 9 deletions(-)

diff --git a/tools/perf/util/comm.c b/tools/perf/util/comm.c
index 21b7ff382c3f..32837b6f7879 100644
--- a/tools/perf/util/comm.c
+++ b/tools/perf/util/comm.c
@@ -2,12 +2,12 @@
 #include "util.h"
 #include <stdlib.h>
 #include <stdio.h>
-#include <linux/atomic.h>
+#include <linux/refcount.h>
 
 struct comm_str {
 	char *str;
 	struct rb_node rb_node;
-	atomic_t refcnt;
+	refcount_t refcnt;
 };
 
 /* Should perhaps be moved to struct machine */
@@ -16,13 +16,13 @@ static struct rb_root comm_str_root;
 static struct comm_str *comm_str__get(struct comm_str *cs)
 {
 	if (cs)
-		atomic_inc(&cs->refcnt);
+		refcount_inc(&cs->refcnt);
 	return cs;
 }
 
 static void comm_str__put(struct comm_str *cs)
 {
-	if (cs && atomic_dec_and_test(&cs->refcnt)) {
+	if (cs && refcount_dec_and_test(&cs->refcnt)) {
 		rb_erase(&cs->rb_node, &comm_str_root);
 		zfree(&cs->str);
 		free(cs);
@@ -43,7 +43,7 @@ static struct comm_str *comm_str__alloc(const char *str)
 		return NULL;
 	}
 
-	atomic_set(&cs->refcnt, 0);
+	refcount_set(&cs->refcnt, 1);
 
 	return cs;
 }
@@ -61,7 +61,7 @@ static struct comm_str *comm_str__findnew(const char *str, struct rb_root *root)
 
 		cmp = strcmp(str, iter->str);
 		if (!cmp)
-			return iter;
+			return comm_str__get(iter);
 
 		if (cmp < 0)
 			p = &(*p)->rb_left;
@@ -95,8 +95,6 @@ struct comm *comm__new(const char *str, u64 timestamp, bool exec)
 		return NULL;
 	}
 
-	comm_str__get(comm->comm_str);
-
 	return comm;
 }
 
@@ -108,7 +106,6 @@ int comm__override(struct comm *comm, const char *str, u64 timestamp, bool exec)
 	if (!new)
 		return -ENOMEM;
 
-	comm_str__get(new);
 	comm_str__put(old);
 	comm->comm_str = new;
 	comm->start = timestamp;
-- 
2.9.3