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Fix race between first rand(3) calls with _once().

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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
This commit is contained in:
Alexander Motin 2021-07-21 11:25:46 -04:00
parent 2ae65d449f
commit 3a57f08b50
1 changed files with 5 additions and 4 deletions
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9
lib/libc/stdlib/rand.c
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@ -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);
}