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Fix race between first rand(3) calls.

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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.

MFC after:	1 month
This commit is contained in:
Alexander Motin 2021-07-20 13:15:08 -04:00
parent 5a9e5a5111
commit 28d70deaaf
1 changed files with 7 additions and 2 deletions
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9
lib/libc/stdlib/rand.c
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@ -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