Date: Wed, 21 Jul 2021 15:32:28 GMT From: Alexander Motin <mav@FreeBSD.org> To: src-committers@FreeBSD.org, dev-commits-src-all@FreeBSD.org, dev-commits-src-main@FreeBSD.org Subject: git: 3a57f08b5042 - main - Fix race between first rand(3) calls with _once(). Message-ID: <202107211532.16LFWS55025500@gitrepo.freebsd.org>
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The branch main has been updated by mav: URL: https://cgit.FreeBSD.org/src/commit/?id=3a57f08b5042f15bb8ffb2fcce99d082d225d4cf commit 3a57f08b5042f15bb8ffb2fcce99d082d225d4cf Author: Alexander Motin <mav@FreeBSD.org> AuthorDate: 2021-07-21 15:25:46 +0000 Commit: Alexander Motin <mav@FreeBSD.org> CommitDate: 2021-07-21 15:32:22 +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 --- 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); }
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