git: 28d70deaafa6 - main - Fix race between first rand(3) calls.

[Alexander Motin]

The branch main has been updated by mav:

URL: https://cgit.FreeBSD.org/src/commit/?id=28d70deaafa62c5d1602de5272c0aad0fcca8aff

commit 28d70deaafa62c5d1602de5272c0aad0fcca8aff
Author:     Alexander Motin <mav at FreeBSD.org>
AuthorDate: 2021-07-20 17:15:08 +0000
Commit:     Alexander Motin <mav at FreeBSD.org>
CommitDate: 2021-07-20 17:30:28 +0000

    Fix race between first rand(3) calls.
    
    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.
    
    MFC after:      1 month
---
 lib/libc/stdlib/rand.c | 9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/lib/libc/stdlib/rand.c b/lib/libc/stdlib/rand.c
index bddb0f040302..353f59349e1d 100644
--- a/lib/libc/stdlib/rand.c
+++ b/lib/libc/stdlib/rand.c
@@ -44,6 +44,7 @@ __FBSDID("$FreeBSD$");
 #include <stdbool.h>
 #include <stdlib.h>
 #include <syslog.h>
+#include <machine/atomic.h>
 #include "un-namespace.h"
 
 #include "random.h"
@@ -68,11 +69,15 @@ static struct __random_state *rand3_state;
 static void
 initialize_rand3(void)
 {
+	struct __random_state *state;
 	int error;
 
-	rand3_state = allocatestate(TYPE_3);
-	error = initstate_r(rand3_state, 1, rand3_state->rst_randtbl, BREAK_3);
+	state = allocatestate(TYPE_3);
+	error = initstate_r(state, 1, state->rst_randtbl, BREAK_3);
 	assert(error == 0);
+	if (!atomic_cmpset_rel_ptr((volatile uintptr_t *)&rand3_state,
+	    (uintptr_t)NULL, (uintptr_t)state))
+		free(state);
 }
 
 int