bionic: fix pthread_mutex_timedlock for PI mutexes
FUTEX_LOCK_PI uses CLOCK_REALTIME so adjust clock timebase
accordingly.
FUTEX_WAIT_BITSET, FUTEX_WAIT_REQUEUE_PI, FUTEX_LOCK_PI2
are updated to check the presence of FUTEX_CLOCK_REALTIME flag.
Test: atest bionic-unit-tests
Bug: 312787238
Bug: 315897315
Change-Id: I2d93286cf22d3b3d9f3757d49b46f7ee9ea5490c
diff --git a/libc/bionic/bionic_futex.cpp b/libc/bionic/bionic_futex.cpp
index 0ac1f6e..aa8234f 100644
--- a/libc/bionic/bionic_futex.cpp
+++ b/libc/bionic/bionic_futex.cpp
@@ -28,6 +28,7 @@
#include "private/bionic_futex.h"
+#include <stdatomic.h>
#include <time.h>
#include "private/bionic_time_conversions.h"
@@ -35,7 +36,6 @@
static inline __always_inline int FutexWithTimeout(volatile void* ftx, int op, int value,
bool use_realtime_clock,
const timespec* abs_timeout, int bitset) {
- const timespec* futex_abs_timeout = abs_timeout;
// pthread's and semaphore's default behavior is to use CLOCK_REALTIME, however this behavior is
// essentially never intended, as that clock is prone to change discontinuously.
//
@@ -46,16 +46,26 @@
// We have seen numerous bugs directly attributable to this difference. Therefore, we provide
// this general workaround to always use CLOCK_MONOTONIC for waiting, regardless of what the input
// timespec is.
- timespec converted_monotonic_abs_timeout;
- if (abs_timeout && use_realtime_clock) {
- monotonic_time_from_realtime_time(converted_monotonic_abs_timeout, *abs_timeout);
- if (converted_monotonic_abs_timeout.tv_sec < 0) {
+ timespec converted_timeout;
+ if (abs_timeout) {
+ if ((op & FUTEX_CMD_MASK) == FUTEX_LOCK_PI) {
+ if (!use_realtime_clock) {
+ realtime_time_from_monotonic_time(converted_timeout, *abs_timeout);
+ abs_timeout = &converted_timeout;
+ }
+ } else {
+ op &= ~FUTEX_CLOCK_REALTIME;
+ if (use_realtime_clock) {
+ monotonic_time_from_realtime_time(converted_timeout, *abs_timeout);
+ abs_timeout = &converted_timeout;
+ }
+ }
+ if (abs_timeout->tv_sec < 0) {
return -ETIMEDOUT;
}
- futex_abs_timeout = &converted_monotonic_abs_timeout;
}
- return __futex(ftx, op, value, futex_abs_timeout, bitset);
+ return __futex(ftx, op, value, abs_timeout, bitset);
}
int __futex_wait_ex(volatile void* ftx, bool shared, int value, bool use_realtime_clock,
@@ -66,6 +76,22 @@
int __futex_pi_lock_ex(volatile void* ftx, bool shared, bool use_realtime_clock,
const timespec* abs_timeout) {
- return FutexWithTimeout(ftx, (shared ? FUTEX_LOCK_PI : FUTEX_LOCK_PI_PRIVATE), 0,
- use_realtime_clock, abs_timeout, 0);
+ // We really want FUTEX_LOCK_PI2 which is default CLOCK_MONOTONIC, but that isn't supported
+ // on linux before 5.14. FUTEX_LOCK_PI uses CLOCK_REALTIME. Here we verify support.
+
+ static atomic_int lock_op = 0;
+ int op = atomic_load_explicit(&lock_op, memory_order_relaxed);
+ if (op == 0) {
+ uint32_t tmp = 0;
+ if (__futex(&tmp, FUTEX_LOCK_PI2, 0, nullptr, 0) == 0) {
+ __futex(&tmp, FUTEX_UNLOCK_PI, 0, nullptr, 0);
+ op = FUTEX_LOCK_PI2;
+ } else {
+ op = FUTEX_LOCK_PI;
+ }
+ atomic_store_explicit(&lock_op, op, memory_order_relaxed);
+ }
+
+ if (!shared) op |= FUTEX_PRIVATE_FLAG;
+ return FutexWithTimeout(ftx, op, 0 /* value */, use_realtime_clock, abs_timeout, 0 /* bitset */);
}
diff --git a/libc/bionic/bionic_time_conversions.cpp b/libc/bionic/bionic_time_conversions.cpp
index d21e12e..9f3c50d 100644
--- a/libc/bionic/bionic_time_conversions.cpp
+++ b/libc/bionic/bionic_time_conversions.cpp
@@ -52,23 +52,32 @@
tv.tv_usec = ts.tv_nsec / 1000;
}
-void monotonic_time_from_realtime_time(timespec& monotonic_time, const timespec& realtime_time) {
- monotonic_time = realtime_time;
+static void convert_timespec_clocks(timespec& new_time, clockid_t new_clockbase,
+ const timespec& old_time, clockid_t old_clockbase) {
+ // get reference clocks
+ timespec new_clock;
+ clock_gettime(new_clockbase, &new_clock);
+ timespec old_clock;
+ clock_gettime(old_clockbase, &old_clock);
- timespec cur_monotonic_time;
- clock_gettime(CLOCK_MONOTONIC, &cur_monotonic_time);
- timespec cur_realtime_time;
- clock_gettime(CLOCK_REALTIME, &cur_realtime_time);
+ // compute new time by moving old delta to the new clock.
+ new_time.tv_sec = old_time.tv_sec - old_clock.tv_sec + new_clock.tv_sec;
+ new_time.tv_nsec = old_time.tv_nsec - old_clock.tv_nsec + new_clock.tv_nsec;
- monotonic_time.tv_nsec -= cur_realtime_time.tv_nsec;
- monotonic_time.tv_nsec += cur_monotonic_time.tv_nsec;
- if (monotonic_time.tv_nsec >= NS_PER_S) {
- monotonic_time.tv_nsec -= NS_PER_S;
- monotonic_time.tv_sec += 1;
- } else if (monotonic_time.tv_nsec < 0) {
- monotonic_time.tv_nsec += NS_PER_S;
- monotonic_time.tv_sec -= 1;
+ // correct nsec to second wrap.
+ if (new_time.tv_nsec >= NS_PER_S) {
+ new_time.tv_nsec -= NS_PER_S;
+ new_time.tv_sec += 1;
+ } else if (new_time.tv_nsec < 0) {
+ new_time.tv_nsec += NS_PER_S;
+ new_time.tv_sec -= 1;
}
- monotonic_time.tv_sec -= cur_realtime_time.tv_sec;
- monotonic_time.tv_sec += cur_monotonic_time.tv_sec;
+}
+
+void monotonic_time_from_realtime_time(timespec& monotonic_time, const timespec& realtime_time) {
+ convert_timespec_clocks(monotonic_time, CLOCK_MONOTONIC, realtime_time, CLOCK_REALTIME);
+}
+
+void realtime_time_from_monotonic_time(timespec& realtime_time, const timespec& monotonic_time) {
+ convert_timespec_clocks(realtime_time, CLOCK_REALTIME, monotonic_time, CLOCK_MONOTONIC);
}
diff --git a/libc/private/bionic_constants.h b/libc/private/bionic_constants.h
index 05914f4..6274fe2 100644
--- a/libc/private/bionic_constants.h
+++ b/libc/private/bionic_constants.h
@@ -16,7 +16,7 @@
#pragma once
-#define NS_PER_S 1000000000
+#define NS_PER_S 1'000'000'000LL
// Size of the shadow call stack. This can be small because these stacks only
// contain return addresses. This must be a power of 2 so the mask trick works.
diff --git a/libc/private/bionic_time_conversions.h b/libc/private/bionic_time_conversions.h
index fb049f2..c6b3c78 100644
--- a/libc/private/bionic_time_conversions.h
+++ b/libc/private/bionic_time_conversions.h
@@ -45,6 +45,9 @@
__LIBC_HIDDEN__ void monotonic_time_from_realtime_time(timespec& monotonic_time,
const timespec& realtime_time);
+__LIBC_HIDDEN__ void realtime_time_from_monotonic_time(timespec& realtime_time,
+ const timespec& monotonic_time);
+
__END_DECLS
static inline int check_timespec(const timespec* ts, bool null_allowed) {