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To: src-committers@FreeBSD.org, dev-commits-src-all@FreeBSD.org,
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From: Alexander Motin <mav@FreeBSD.org>
Subject: git: 09d4fe40e039 - stable/13 - Fix race between first rand(3) calls
with _once().
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The branch stable/13 has been updated by mav:
URL: https://cgit.FreeBSD.org/src/commit/?id=09d4fe40e039d4b08a034454c36aed86571725b0
commit 09d4fe40e039d4b08a034454c36aed86571725b0
Author: Alexander Motin <mav@FreeBSD.org>
AuthorDate: 2021-07-21 15:25:46 +0000
Commit: Alexander Motin <mav@FreeBSD.org>
CommitDate: 2021-08-19 01:11:51 +0000
Fix race between first rand(3) calls with _once().
Before this patch there was a chance for thread that called rand(3)
slightly later to see rand3_state already allocated, but not yet
initialized. While this API is not expected to be thread-safe, it
is not expected to crash. ztest on 64-thread system reproduced it
reliably for me.
Submitted by: avg@
MFC after: 1 month
(cherry picked from commit 3a57f08b5042f15bb8ffb2fcce99d082d225d4cf)
---
lib/libc/stdlib/rand.c | 9 +++++----
1 file changed, 5 insertions(+), 4 deletions(-)
diff --git a/lib/libc/stdlib/rand.c b/lib/libc/stdlib/rand.c
index bddb0f040302..e448d1b1fd14 100644
--- a/lib/libc/stdlib/rand.c
+++ b/lib/libc/stdlib/rand.c
@@ -41,11 +41,13 @@ __FBSDID("$FreeBSD$");
#include <sys/param.h>
#include <sys/sysctl.h>
#include <assert.h>
+#include <pthread.h>
#include <stdbool.h>
#include <stdlib.h>
#include <syslog.h>
#include "un-namespace.h"
+#include "libc_private.h"
#include "random.h"
/*
@@ -64,6 +66,7 @@ __FBSDID("$FreeBSD$");
* the advantage of being the one already in the tree.
*/
static struct __random_state *rand3_state;
+static pthread_once_t rand3_state_once = PTHREAD_ONCE_INIT;
static void
initialize_rand3(void)
@@ -78,16 +81,14 @@ initialize_rand3(void)
int
rand(void)
{
- if (rand3_state == NULL)
- initialize_rand3();
+ _once(&rand3_state_once, initialize_rand3);
return ((int)random_r(rand3_state));
}
void
srand(unsigned seed)
{
- if (rand3_state == NULL)
- initialize_rand3();
+ _once(&rand3_state_once, initialize_rand3);
srandom_r(rand3_state, seed);
}