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Fix nsync_mu_unlock_slow_() on Apple Silicon

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We torture test dlmalloc() in test/libc/stdio/memory_test.c. That test
was crashing on occasion on Apple M1 microprocessors when dlmalloc was
using *NSYNC locks. It was relatively easy to spot the cause, which is
this one particular compare and swap operation, which needed to change
to use sequentially-consistent ordering rather than an acquire barrier
This commit is contained in:
Justine Tunney 2023-11-13 10:57:02 -08:00
parent 3b15d31247
commit 751d20d98d
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GPG key ID: BE714B4575D6E328
5 changed files with 36 additions and 2 deletions
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2
third_party/nsync/README.cosmo vendored
View file

@ -15,6 +15,8 @@ ORIGIN
LOCAL CHANGES
- Fix nsync_mu_unlock() on Apple Silicon
- Time APIs were so good that they're now in libc
- Double linked list API was so good that it's now in libc

8
third_party/nsync/atomic.internal.h vendored
View file

@ -86,6 +86,13 @@ static inline int atm_cas_relacq_u32_(nsync_atomic_uint32_ *p, uint32_t o,
memory_order_relaxed);
}
static inline int atm_cas_seqcst_u32_(nsync_atomic_uint32_ *p, uint32_t o,
uint32_t n) {
return atomic_compare_exchange_strong_explicit(NSYNC_ATOMIC_UINT32_PTR_(p),
&o, n, memory_order_seq_cst,
memory_order_relaxed);
}
#define ATM_CAS_HELPER_(barrier, p, o, n) \
(atm_cas_##barrier##_u32_((p), (o), (n)))
@ -93,6 +100,7 @@ static inline int atm_cas_relacq_u32_(nsync_atomic_uint32_ *p, uint32_t o,
#define ATM_CAS_ACQ(p, o, n) ATM_CAS_HELPER_(acq, (p), (o), (n))
#define ATM_CAS_REL(p, o, n) ATM_CAS_HELPER_(rel, (p), (o), (n))
#define ATM_CAS_RELACQ(p, o, n) ATM_CAS_HELPER_(relacq, (p), (o), (n))
#define ATM_CAS_SEQCST(p, o, n) ATM_CAS_HELPER_(seqcst, (p), (o), (n))
/* Need a cast to remove "const" from some uses. */
#define ATM_LOAD(p) \

4
third_party/nsync/mu.c vendored
View file

@ -298,8 +298,8 @@ void nsync_mu_unlock_slow_ (nsync_mu *mu, lock_type *l_type) {
return;
}
} else if ((old_word&MU_SPINLOCK) == 0 &&
ATM_CAS_ACQ (&mu->word, old_word,
(old_word-early_release_mu)|MU_SPINLOCK|MU_DESIG_WAKER)) {
ATM_CAS_SEQCST (&mu->word, old_word, /* [jart] fixes issues on apple silicon */
(old_word-early_release_mu)|MU_SPINLOCK|MU_DESIG_WAKER)) {
struct Dll *wake;
lock_type *wake_type;
uint32_t clear_on_release;