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Harden against aba problem

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Justine Tunney 2024-08-26 19:59:25 -07:00
parent 610c951f71
commit 884d89235f
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GPG key ID: BE714B4575D6E328
8 changed files with 212 additions and 85 deletions
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65
third_party/nsync/common.c vendored
View file

@ -15,6 +15,7 @@
│ See the License for the specific language governing permissions and │
│ limitations under the License. │
╚─────────────────────────────────────────────────────────────────────────────*/
#include "libc/atomic.h"
#include "libc/calls/calls.h"
#include "libc/calls/syscall-sysv.internal.h"
#include "libc/dce.h"
@ -136,14 +137,45 @@ waiter *nsync_dll_waiter_samecond_ (struct Dll *e) {
/* -------------------------------- */
static _Atomic(waiter *) free_waiters;
#define MASQUE 0x00fffffffffffff8
#define PTR(x) ((uintptr_t)(x) & MASQUE)
#define TAG(x) ROL((uintptr_t)(x) & ~MASQUE, 8)
#define ABA(p, t) ((uintptr_t)(p) | (ROR((uintptr_t)(t), 8) & ~MASQUE))
#define ROL(x, n) (((x) << (n)) | ((x) >> (64 - (n))))
#define ROR(x, n) (((x) >> (n)) | ((x) << (64 - (n))))
static atomic_uintptr_t free_waiters;
static void free_waiters_push (waiter *w) {
int backoff = 0;
w->next_free = atomic_load_explicit (&free_waiters, memory_order_relaxed);
while (!atomic_compare_exchange_weak_explicit (&free_waiters, &w->next_free, w,
memory_order_acq_rel, memory_order_relaxed))
backoff = pthread_delay_np (free_waiters, backoff);
uintptr_t tip;
ASSERT (!TAG(w));
tip = atomic_load_explicit (&free_waiters, memory_order_relaxed);
for (;;) {
w->next_free = (waiter *) PTR (tip);
if (atomic_compare_exchange_weak_explicit (&free_waiters,
&tip,
ABA (w, TAG (tip) + 1),
memory_order_release,
memory_order_relaxed))
break;
pthread_pause_np ();
}
}
static waiter *free_waiters_pop (void) {
waiter *w;
uintptr_t tip;
tip = atomic_load_explicit (&free_waiters, memory_order_relaxed);
while ((w = (waiter *) PTR (tip))) {
if (atomic_compare_exchange_weak_explicit (&free_waiters,
&tip,
ABA (w->next_free, TAG (tip) + 1),
memory_order_acquire,
memory_order_relaxed))
break;
pthread_pause_np ();
}
return w;
}
static void free_waiters_populate (void) {
@ -172,30 +204,12 @@ static void free_waiters_populate (void) {
}
w->nw.sem = &w->sem;
dll_init (&w->nw.q);
NSYNC_ATOMIC_UINT32_STORE_ (&w->nw.waiting, 0);
w->nw.flags = NSYNC_WAITER_FLAG_MUCV;
ATM_STORE (&w->remove_count, 0);
dll_init (&w->same_condition);
w->flags = 0;
free_waiters_push (w);
}
}
static waiter *free_waiters_pop (void) {
waiter *w;
int backoff = 0;
for (;;) {
if ((w = atomic_load_explicit (&free_waiters, memory_order_relaxed))) {
if (atomic_compare_exchange_weak_explicit (&free_waiters, &w, w->next_free,
memory_order_acq_rel, memory_order_relaxed))
return w;
backoff = pthread_delay_np (free_waiters, backoff);
} else {
free_waiters_populate ();
}
}
}
/* -------------------------------- */
#define waiter_for_thread __get_tls()->tib_nsync
@ -221,7 +235,8 @@ waiter *nsync_waiter_new_ (void) {
tw = waiter_for_thread;
w = tw;
if (w == NULL || (w->flags & (WAITER_RESERVED|WAITER_IN_USE)) != WAITER_RESERVED) {
w = free_waiters_pop ();
while (!(w = free_waiters_pop ()))
free_waiters_populate ();
if (tw == NULL) {
w->flags |= WAITER_RESERVED;
waiter_for_thread = w;

6
third_party/nsync/mu_semaphore_sem.c vendored
View file

@ -52,11 +52,11 @@ static nsync_semaphore *sem_big_enough_for_sem = (nsync_semaphore *) (uintptr_t)
(sizeof (struct sem) <= sizeof (*sem_big_enough_for_sem)));
static void sems_push (struct sem *f) {
int backoff = 0;
f->next = atomic_load_explicit (&g_sems, memory_order_relaxed);
while (!atomic_compare_exchange_weak_explicit (&g_sems, &f->next, f,
memory_order_acq_rel, memory_order_relaxed))
backoff = pthread_delay_np (&g_sems, backoff);
memory_order_acq_rel,
memory_order_relaxed))
pthread_pause_np ();
}
static bool nsync_mu_semaphore_sem_create (struct sem *f) {