On Tue, Jul 20, 2021 at 05:30:33PM +0000, Alexander Motin wrote: > The branch main has been updated by mav: > > URL: > https://cgit.FreeBSD.org/src/commit/?id=28d70deaafa62c5d1602de5272c0aad0fcca8aff > > commit 28d70deaafa62c5d1602de5272c0aad0fcca8aff > Author: Alexander Motin <m...@freebsd.org> > AuthorDate: 2021-07-20 17:15:08 +0000 > Commit: Alexander Motin <m...@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); For this to have effect on less ordered architectures (AKA non-x86), at least reads of rand3_state should be atomic_load_acq().
But consider using _once() in libc, which takes care about ordering/threads. > } > > int _______________________________________________ dev-commits-src-main@freebsd.org mailing list https://lists.freebsd.org/mailman/listinfo/dev-commits-src-main To unsubscribe, send any mail to "dev-commits-src-main-unsubscr...@freebsd.org"
