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selftests: futex: Add tests for robust release operations

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Add tests for __vdso_futex_robust_listXX_try_unlock() and for the futex()
op FUTEX_ROBUST_UNLOCK.

Test the contended and uncontended cases for the vDSO functions and all
ops combinations for FUTEX_ROBUST_UNLOCK.

[ tglx: Replace the VDSO function lookup ]

Signed-off-by: André Almeida <andrealmeid@igalia.com>
Signed-off-by: Thomas Gleixner <tglx@kernel.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://patch.msgid.link/20260329-tonyk-vdso_test-v2-2-b7db810e44a1@igalia.com
Link: https://patch.msgid.link/20260602090535.988101541@kernel.org
This commit is contained in:
André Almeida
2026-06-02 11:10:21 +02:00
committed by Peter Zijlstra
parent 3f63e25459
commit 608323bf7b
2 changed files with 245 additions and 0 deletions
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239
tools/testing/selftests/futex/functional/robust_list.c
View File

@@ -27,12 +27,15 @@
#include "futextest.h"
#include "../../kselftest_harness.h"
#include <dlfcn.h>
#include <errno.h>
#include <pthread.h>
#include <signal.h>
#include <stdint.h>
#include <stdatomic.h>
#include <stdbool.h>
#include <stddef.h>
#include <sys/auxv.h>
#include <sys/mman.h>
#include <sys/wait.h>
@@ -42,6 +45,10 @@
#define SLEEP_US 100
#if __SIZEOF_LONG__ == 8
# define BUILD_64
#endif
static pthread_barrier_t barrier, barrier2;
static int set_robust_list(struct robust_list_head *head, size_t len)
@@ -54,6 +61,12 @@ static int get_robust_list(int pid, struct robust_list_head **head, size_t *len_
return syscall(SYS_get_robust_list, pid, head, len_ptr);
}
static int sys_futex_robust_unlock(_Atomic(uint32_t) *uaddr, unsigned int op, int val,
void *list_op_pending, unsigned int val3)
{
return syscall(SYS_futex, uaddr, op, val, NULL, list_op_pending, val3, 0);
}
/*
* Basic lock struct, contains just the futex word and the robust list element
* Real implementations have also a *prev to easily walk in the list
@@ -549,4 +562,230 @@ TEST(test_circular_list)
ksft_test_result_pass("%s\n", __func__);
}
/*
* Below are tests for the fix of robust release race condition. Please read the following
* thread to learn more about the issue in the first place and why the following functions fix it:
* https://lore.kernel.org/lkml/20260316162316.356674433@kernel.org/
*/
/*
* Auxiliary code for binding the vDSO functions
*/
static void *get_vdso_func_addr(const char *function)
{
const char *vdso_names[] = {
"linux-vdso.so.1", "linux-gate.so.1", "linux-vdso32.so.1", "linux-vdso64.so.1",
};
for (int i = 0; i < ARRAY_SIZE(vdso_names); i++) {
void *vdso = dlopen(vdso_names[i], RTLD_LAZY | RTLD_LOCAL | RTLD_NOLOAD);
if (vdso)
return dlsym(vdso, function);
}
return NULL;
}
/*
* These are the real vDSO function signatures:
*
* __vdso_futex_robust_list64_try_unlock(__u32 *lock, __u32 tid, __u64 *pop)
* __vdso_futex_robust_list32_try_unlock(__u32 *lock, __u32 tid, __u32 *pop)
*
* So for the generic entry point we need to use a void pointer as the last argument
*/
FIXTURE(vdso_unlock)
{
uint32_t (*vdso)(_Atomic(uint32_t) *lock, uint32_t tid, void *pop);
};
FIXTURE_VARIANT(vdso_unlock)
{
bool is_32;
char func_name[];
};
FIXTURE_SETUP(vdso_unlock)
{
self->vdso = get_vdso_func_addr(variant->func_name);
}
FIXTURE_TEARDOWN(vdso_unlock) {}
FIXTURE_VARIANT_ADD(vdso_unlock, 32)
{
.func_name = "__vdso_futex_robust_list32_try_unlock",
.is_32 = true,
};
FIXTURE_VARIANT_ADD(vdso_unlock, 64)
{
.func_name = "__vdso_futex_robust_list64_try_unlock",
.is_32 = false,
};
/*
* Test the vDSO robust_listXX_try_unlock() for the uncontended case. The virtual syscall should
* return the thread ID of the lock owner, the lock word must be 0 and the list_op_pending should
* be NULL.
*/
TEST_F(vdso_unlock, test_robust_try_unlock_uncontended)
{
struct lock_struct lock = { .futex = 0 };
_Atomic(unsigned int) *futex = &lock.futex;
struct robust_list_head head;
uintptr_t exp = (uintptr_t) NULL;
pid_t tid = gettid();
int ret;
if (!self->vdso) {
ksft_test_result_skip("%s not found\n", variant->func_name);
return;
}
*futex = tid;
ret = set_list(&head);
if (ret)
ksft_test_result_fail("set_robust_list error\n");
head.list_op_pending = &lock.list;
ret = self->vdso(futex, tid, &head.list_op_pending);
ASSERT_EQ(ret, tid);
ASSERT_EQ(*futex, 0);
/* Check only the lower 32 bits for the 32-bit entry point */
if (variant->is_32) {
exp = (uintptr_t)(unsigned long)&lock.list;
exp &= ~0xFFFFFFFFULL;
}
ASSERT_EQ((uintptr_t)(unsigned long)head.list_op_pending, exp);
}
/*
* If the lock is contended, the operation fails. The return value is the value found at the
* futex word (tid | FUTEX_WAITERS), the futex word is not modified and the list_op_pending is_32
* not cleared.
*/
TEST_F(vdso_unlock, test_robust_try_unlock_contended)
{
struct lock_struct lock = { .futex = 0 };
_Atomic(unsigned int) *futex = &lock.futex;
struct robust_list_head head;
pid_t tid = gettid();
int ret;
if (!self->vdso) {
ksft_test_result_skip("%s not found\n", variant->func_name);
return;
}
*futex = tid | FUTEX_WAITERS;
ret = set_list(&head);
if (ret)
ksft_test_result_fail("set_robust_list error\n");
head.list_op_pending = &lock.list;
ret = self->vdso(futex, tid, &head.list_op_pending);
ASSERT_EQ(ret, tid | FUTEX_WAITERS);
ASSERT_EQ(*futex, tid | FUTEX_WAITERS);
ASSERT_EQ(head.list_op_pending, &lock.list);
}
FIXTURE(futex_op) {};
FIXTURE_VARIANT(futex_op)
{
unsigned int op;
unsigned int val3;
};
FIXTURE_SETUP(futex_op) {}
FIXTURE_TEARDOWN(futex_op) {}
FIXTURE_VARIANT_ADD(futex_op, wake)
{
.op = FUTEX_WAKE,
.val3 = 0,
};
FIXTURE_VARIANT_ADD(futex_op, wake_bitset)
{
.op = FUTEX_WAKE_BITSET,
.val3 = FUTEX_BITSET_MATCH_ANY,
};
FIXTURE_VARIANT_ADD(futex_op, unlock_pi)
{
.op = FUTEX_UNLOCK_PI,
.val3 = 0,
};
FIXTURE_VARIANT_ADD(futex_op, wake32)
{
.op = FUTEX_WAKE | FUTEX_ROBUST_LIST32,
.val3 = 0,
};
FIXTURE_VARIANT_ADD(futex_op, wake_bitset32)
{
.op = FUTEX_WAKE_BITSET | FUTEX_ROBUST_LIST32,
.val3 = FUTEX_BITSET_MATCH_ANY,
};
FIXTURE_VARIANT_ADD(futex_op, unlock_pi32)
{
.op = FUTEX_UNLOCK_PI | FUTEX_ROBUST_LIST32,
.val3 = 0,
};
/*
* The syscall should return the number of tasks waken (for this test, 0), clear the futex word and
* clear list_op_pending
*/
TEST_F(futex_op, test_futex_robust_unlock)
{
struct lock_struct lock = { .futex = 0 };
_Atomic(unsigned int) *futex = &lock.futex;
uintptr_t exp = (uintptr_t) NULL;
struct robust_list_head head;
pid_t tid = gettid();
int ret;
#ifndef BUILD_64
if (!(variant->op & FUTEX_ROBUST_LIST32)) {
ksft_test_result_skip("Not supported for 32 bit build\n");
return;
}
#endif
*futex = tid | FUTEX_WAITERS;
ret = set_list(&head);
if (ret)
ksft_test_result_fail("set_robust_list error\n");
head.list_op_pending = &lock.list;
ret = sys_futex_robust_unlock(futex, FUTEX_ROBUST_UNLOCK | variant->op, tid,
&head.list_op_pending, variant->val3);
ASSERT_EQ(ret, 0);
ASSERT_EQ(*futex, 0);
if (variant->op & FUTEX_ROBUST_LIST32) {
exp = (uint64_t)(unsigned long)&lock.list;
exp &= ~0xFFFFFFFFULL;
}
ASSERT_EQ((uintptr_t)(unsigned long)head.list_op_pending, exp);
}
TEST_HARNESS_MAIN

6
tools/testing/selftests/futex/include/futextest.h
View File

@@ -38,6 +38,12 @@ typedef volatile u_int32_t futex_t;
#ifndef FUTEX_CMP_REQUEUE_PI
#define FUTEX_CMP_REQUEUE_PI 12
#endif
#ifndef FUTEX_ROBUST_UNLOCK
#define FUTEX_ROBUST_UNLOCK 512
#endif
#ifndef FUTEX_ROBUST_LIST32
#define FUTEX_ROBUST_LIST32 1024
#endif
#ifndef FUTEX_WAIT_REQUEUE_PI_PRIVATE
#define FUTEX_WAIT_REQUEUE_PI_PRIVATE (FUTEX_WAIT_REQUEUE_PI | \
FUTEX_PRIVATE_FLAG)