[PATCH RESEND v4 0/7] futex: Create set_robust_list2

[PATCH RESEND v4 0/7] futex: Create set_robust_list2

[André Almeida]

This patch adds a new robust_list() syscall. The current syscall
can't be expanded to cover the following use case, so a new one is
needed. This new syscall allows users to set multiple robust lists per
process and to have either 32bit or 64bit pointers in the list.

* Use case

FEX-Emu[1] is an application that runs x86 and x86-64 binaries on an
AArch64 Linux host. One of the tasks of FEX-Emu is to translate syscalls
from one platform to another. Existing set_robust_list() can't be easily
translated because of two limitations:

1) x86 apps can have 32bit pointers robust lists. For a x86-64 kernel
   this is not a problem, because of the compat entry point. But there's
   no such compat entry point for AArch64, so the kernel would do the
   pointer arithmetic wrongly. Is also unviable to userspace to keep
   track every addition/removal to the robust list and keep a 64bit
   version of it somewhere else to feed the kernel. Thus, the new
   interface has an option of telling the kernel if the list is filled
   with 32bit or 64bit pointers.

2) Apps can set just one robust list (in theory, x86-64 can set two if
   they also use the compat entry point). That means that when a x86 app
   asks FEX-Emu to call set_robust_list(), FEX have two options: to
   overwrite their own robust list pointer and make the app robust, or
   to ignore the app robust list and keep the emulator robust. The new
   interface allows for multiple robust lists per application, solving
   this.

* Interface

This is the proposed interface:

	long set_robust_list2(void *head, int index, unsigned int flags)

`head` is the head of the userspace struct robust_list_head, just as old
set_robust_list(). It needs to be a void pointer since it can point to a normal
robust_list_head or a compat_robust_list_head.

`flags` can be used for defining the list type:

	enum robust_list_type {
	 	ROBUST_LIST_32BIT,
		ROBUST_LIST_64BIT,
	 };

`index` is the index in the internal robust_list's linked list (the naming
starts to get confusing, I reckon). If `index == -1`, that means that user wants
to set a new robust_list, and the kernel will append it in the end of the list,
assign a new index and return this index to the user. If `index >= 0`, that
means that user wants to re-set `*head` of an already existing list (similarly
to what happens when you call set_robust_list() twice with different `*head`).

If `index` is out of range, or it points to a non-existing robust_list, or if
the internal list is full, an error is returned.

* Implementation

The implementation re-uses most of the existing robust list interface as
possible. The new task_struct member `struct list_head robust_list2` is just a
linked list where new lists are appended as the user requests more lists, and by
futex_cleanup(), the kernel walks through the internal list feeding
exit_robust_list() with the robust_list's.

This implementation supports up to 10 lists (defined at ROBUST_LISTS_PER_TASK),
but it was an arbitrary number for this RFC. For the described use case above, 4
should be enough, I'm not sure which should be the limit.

It doesn't support list removal (should it support?). It doesn't have a proper
get_robust_list2() yet as well, but I can add it in a next revision. We could
also have a generic robust_list() syscall that can be used to set/get and be
controlled by flags.

The new interface has a `unsigned int flags` argument, making it
extensible for future use cases as well.

It refuses unaligned `head` addresses. It doesn't have a limit for elements in a
single list (like ROBUST_LIST_LIMIT), it destroys the list as it is parsed to be
safe against circular lists.

* Testing

This patcheset has a selftest patch that expands this one:
https://lore.kernel.org/lkml/20250212131123.37431-1-andrealmeid@igalia.com/

Also, FEX-Emu added support for this interface to validate it:
https://github.com/FEX-Emu/FEX/pull/3966

Feedback is very welcomed!

Thanks,
	André

[1] https://github.com/FEX-Emu/FEX

Changelog:
- Rebased on top of new futex work (private hash)
v4: https://lore.kernel.org/lkml/20250225183531.682556-1-andrealmeid@igalia.com/

- Refuse unaligned head pointers
- Ignore ROBUST_LIST_LIMIT for lists created with this interface and make it
  robust against circular lists
- Fix a get_robust_list() syscall bug for getting the list from another thread
- Adapt selftest to use the new interface
v3: https://lore.kernel.org/lkml/20241217174958.477692-1-andrealmeid@igalia.com/

- Old syscall set_robust_list() adds new head to the internal linked list of
  robust lists pointers, instead of having a field just for them. Remove
  tsk->robust_list and use only tsk->robust_list2
v2: https://lore.kernel.org/lkml/20241101162147.284993-1-andrealmeid@igalia.com/

- Added a patch to properly deal with exit_robust_list() in 64bit vs 32bit
- Wired-up syscall for all archs
- Added more of the cover letter to the commit message
v1: https://lore.kernel.org/lkml/20241024145735.162090-1-andrealmeid@igalia.com/

---
André Almeida (7):
      selftests/futex: Add ASSERT_ macros
      selftests/futex: Create test for robust list
      futex: Use explicit sizes for compat_exit_robust_list
      futex: Create set_robust_list2
      futex: Wire up set_robust_list2 syscall
      futex: Remove the limit of elements for sys_set_robust_list2 lists
      selftests: futex: Expand robust list test for the new interface

 arch/alpha/kernel/syscalls/syscall.tbl             |   1 +
 arch/arm/tools/syscall.tbl                         |   1 +
 arch/m68k/kernel/syscalls/syscall.tbl              |   1 +
 arch/microblaze/kernel/syscalls/syscall.tbl        |   1 +
 arch/mips/kernel/syscalls/syscall_n32.tbl          |   1 +
 arch/mips/kernel/syscalls/syscall_n64.tbl          |   1 +
 arch/mips/kernel/syscalls/syscall_o32.tbl          |   1 +
 arch/parisc/kernel/syscalls/syscall.tbl            |   1 +
 arch/powerpc/kernel/syscalls/syscall.tbl           |   1 +
 arch/s390/kernel/syscalls/syscall.tbl              |   1 +
 arch/sh/kernel/syscalls/syscall.tbl                |   1 +
 arch/sparc/kernel/syscalls/syscall.tbl             |   1 +
 arch/x86/entry/syscalls/syscall_32.tbl             |   1 +
 arch/x86/entry/syscalls/syscall_64.tbl             |   1 +
 arch/xtensa/kernel/syscalls/syscall.tbl            |   1 +
 include/linux/compat.h                             |  12 +-
 include/linux/futex.h                              |  16 +-
 include/linux/sched.h                              |   5 +-
 include/uapi/asm-generic/unistd.h                  |   2 +
 include/uapi/linux/futex.h                         |  24 +
 kernel/futex/core.c                                | 165 ++++-
 kernel/futex/futex.h                               |   5 +
 kernel/futex/syscalls.c                            |  85 ++-
 kernel/sys_ni.c                                    |   1 +
 scripts/syscall.tbl                                |   1 +
 .../testing/selftests/futex/functional/.gitignore  |   1 +
 tools/testing/selftests/futex/functional/Makefile  |   3 +-
 .../selftests/futex/functional/robust_list.c       | 706 +++++++++++++++++++++
 tools/testing/selftests/futex/include/logging.h    |  38 ++
 29 files changed, 1026 insertions(+), 53 deletions(-)
---
base-commit: 3ee84e3dd88e39b55b534e17a7b9a181f1d46809
change-id: 20250225-tonyk-robust_futex-60adeedac695

Best regards,
-- 
André Almeida <andrealmeid@igalia.com>

[PATCH RESEND v4 1/7] selftests/futex: Add ASSERT_ macros

[André Almeida]

Create ASSERT_{EQ, NE, TRUE, FALSE} macros to make test creation easier.

Signed-off-by: André Almeida <andrealmeid@igalia.com>
---
 tools/testing/selftests/futex/include/logging.h | 38 +++++++++++++++++++++++++
 1 file changed, 38 insertions(+)

diff --git a/tools/testing/selftests/futex/include/logging.h b/tools/testing/selftests/futex/include/logging.h
index 874c69ce5cce9efa3a9d6de246f5972a75437dbf..a19755622a877932884570c8f58aaee7371d5f8f 100644
--- a/tools/testing/selftests/futex/include/logging.h
+++ b/tools/testing/selftests/futex/include/logging.h
@@ -23,6 +23,44 @@
 #include <linux/futex.h>
 #include "kselftest.h"
 
+#define ASSERT_EQ(var, value)	\
+do {				\
+	if (var != value) {	\
+		ksft_test_result_fail("%s: expected %ld, but %s has %ld\n", \
+				      __func__, (long) value, #var, \
+				      (long) var); \
+		return;		\
+	}			\
+} while (0)
+
+#define ASSERT_NE(var, value)	\
+do {				\
+	if (var == value) {	\
+		ksft_test_result_fail("%s: expected not %ld, but %s has %ld\n", \
+				      __func__, (long) value, #var, \
+				      (long) var); \
+		return; \
+	}		\
+} while (0)
+
+#define ASSERT_TRUE(var)	\
+do {				\
+	if ((var) == 0) {	\
+		ksft_test_result_fail("%s: expected %s to be true\n", \
+				      __func__, #var); \
+		return;		\
+	}			\
+} while (0)
+
+#define ASSERT_FALSE(var)	\
+do {				\
+	if (var) {		\
+		ksft_test_result_fail("%s: expected %s to be false\n", \
+				      __func__, #var); \
+		return;		\
+	}			\
+} while (0)
+
 /*
  * Define PASS, ERROR, and FAIL strings with and without color escape
  * sequences, default to no color.

-- 
2.49.0

[PATCH RESEND v4 2/7] selftests/futex: Create test for robust list

[André Almeida]

Create a test for the robust list mechanism. Test the following uAPI
operations:

- Creating a robust mutex where the lock waiter is wake by the kernel
  when the lock owner died
- Setting a robust list to the current task
- Getting a robust list from the current task
- Getting a robust list from another task
- Using the list_op_pending field from robust_list_head struct to test
  robustness when the lock owner dies before completing the locking
- Setting a invalid size for syscall argument `len`
- Adding multiple elements to a robust list wait waiting for each of
  them
- Creating a circular list and checking that the kernel does not get
  stuck in an infinity loop

This is the expected output:

 TAP version 13
 1..7
 ok 1 test_robustness
 ok 2 test_set_robust_list_invalid_size
 ok 3 test_get_robust_list_self
 ok 4 test_get_robust_list_child
 ok 5 test_set_list_op_pending
 ok 6 test_robust_list_multiple_elements
 ok 7 test_circular_list
 # Totals: pass:7 fail:0 xfail:0 xpass:0 skip:0 error:0

Signed-off-by: André Almeida <andrealmeid@igalia.com>
---
 .../testing/selftests/futex/functional/.gitignore  |   1 +
 tools/testing/selftests/futex/functional/Makefile  |   3 +-
 .../selftests/futex/functional/robust_list.c       | 554 +++++++++++++++++++++
 3 files changed, 557 insertions(+), 1 deletion(-)

diff --git a/tools/testing/selftests/futex/functional/.gitignore b/tools/testing/selftests/futex/functional/.gitignore
index 7b24ae89594a9db211d4b8469ebcef8d1f7012d8..7f447ebfbc62bbad9add0dc86a75abcdb8a4d9a7 100644
--- a/tools/testing/selftests/futex/functional/.gitignore
+++ b/tools/testing/selftests/futex/functional/.gitignore
@@ -11,3 +11,4 @@ futex_wait_timeout
 futex_wait_uninitialized_heap
 futex_wait_wouldblock
 futex_waitv
+robust_list
diff --git a/tools/testing/selftests/futex/functional/Makefile b/tools/testing/selftests/futex/functional/Makefile
index 8cfb87f7f7c5059c82f1e6290c076d3f13f5ea41..e6fa66e622dee4de74c31c8b9b486ca01de35737 100644
--- a/tools/testing/selftests/futex/functional/Makefile
+++ b/tools/testing/selftests/futex/functional/Makefile
@@ -20,7 +20,8 @@ TEST_GEN_PROGS := \
 	futex_priv_hash \
 	futex_numa_mpol \
 	futex_waitv \
-	futex_numa
+	futex_numa \
+	robust_list
 
 TEST_PROGS := run.sh
 
diff --git a/tools/testing/selftests/futex/functional/robust_list.c b/tools/testing/selftests/futex/functional/robust_list.c
new file mode 100644
index 0000000000000000000000000000000000000000..42690b2440fd29a9b12c46f67f9645ccc93d1147
--- /dev/null
+++ b/tools/testing/selftests/futex/functional/robust_list.c
@@ -0,0 +1,554 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * Copyright (C) 2024 Igalia S.L.
+ *
+ * Robust list test by André Almeida <andrealmeid@igalia.com>
+ *
+ * The robust list uAPI allows userspace to create "robust" locks, in the sense
+ * that if the lock holder thread dies, the remaining threads that are waiting
+ * for the lock won't block forever, waiting for a lock that will never be
+ * released.
+ *
+ * This is achieve by userspace setting a list where a thread can enter all the
+ * locks (futexes) that it is holding. The robust list is a linked list, and
+ * userspace register the start of the list with the syscall set_robust_list().
+ * If such thread eventually dies, the kernel will walk this list, waking up one
+ * thread waiting for each futex and marking the futex word with the flag
+ * FUTEX_OWNER_DIED.
+ *
+ * See also
+ *	man set_robust_list
+ *	Documententation/locking/robust-futex-ABI.rst
+ *	Documententation/locking/robust-futexes.rst
+ */
+
+#define _GNU_SOURCE
+
+#include "futextest.h"
+#include "logging.h"
+
+#include <errno.h>
+#include <pthread.h>
+#include <signal.h>
+#include <stdatomic.h>
+#include <stdbool.h>
+#include <stddef.h>
+#include <sys/mman.h>
+#include <sys/wait.h>
+
+#define STACK_SIZE (1024 * 1024)
+
+#define FUTEX_TIMEOUT 3
+
+static pthread_barrier_t barrier, barrier2;
+
+int set_robust_list(struct robust_list_head *head, size_t len)
+{
+	return syscall(SYS_set_robust_list, head, len);
+}
+
+int get_robust_list(int pid, struct robust_list_head **head, size_t *len_ptr)
+{
+	return syscall(SYS_get_robust_list, pid, head, len_ptr);
+}
+
+/*
+ * 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
+ */
+struct lock_struct {
+	_Atomic(unsigned int) futex;
+	struct robust_list list;
+};
+
+/*
+ * Helper function to spawn a child thread. Returns -1 on error, pid on success
+ */
+static int create_child(int (*fn)(void *arg), void *arg)
+{
+	char *stack;
+	pid_t pid;
+
+	stack = mmap(NULL, STACK_SIZE, PROT_READ | PROT_WRITE,
+		     MAP_PRIVATE | MAP_ANONYMOUS | MAP_STACK, -1, 0);
+	if (stack == MAP_FAILED)
+		return -1;
+
+	stack += STACK_SIZE;
+
+	pid = clone(fn, stack, CLONE_VM | SIGCHLD, arg);
+
+	if (pid == -1)
+		return -1;
+
+	return pid;
+}
+
+/*
+ * Helper function to prepare and register a robust list
+ */
+static int set_list(struct robust_list_head *head)
+{
+	int ret;
+
+	ret = set_robust_list(head, sizeof(struct robust_list_head));
+	if (ret)
+		return ret;
+
+	head->futex_offset = (size_t) offsetof(struct lock_struct, futex) -
+			     (size_t) offsetof(struct lock_struct, list);
+	head->list.next = &head->list;
+	head->list_op_pending = NULL;
+
+	return 0;
+}
+
+/*
+ * A basic (and incomplete) mutex lock function with robustness
+ */
+static int mutex_lock(struct lock_struct *lock, struct robust_list_head *head, bool error_inject)
+{
+	_Atomic(unsigned int) *futex = &lock->futex;
+	unsigned int zero = 0;
+	int ret = -1;
+	pid_t tid = gettid();
+
+	/*
+	 * Set list_op_pending before starting the lock, so the kernel can catch
+	 * the case where the thread died during the lock operation
+	 */
+	head->list_op_pending = &lock->list;
+
+	if (atomic_compare_exchange_strong(futex, &zero, tid)) {
+		/*
+		 * We took the lock, insert it in the robust list
+		 */
+		struct robust_list *list = &head->list;
+
+		/* Error injection to test list_op_pending */
+		if (error_inject)
+			return 0;
+
+		while (list->next != &head->list)
+			list = list->next;
+
+		list->next = &lock->list;
+		lock->list.next = &head->list;
+
+		ret = 0;
+	} else {
+		/*
+		 * We didn't take the lock, wait until the owner wakes (or dies)
+		 */
+		struct timespec to;
+
+		to.tv_sec = FUTEX_TIMEOUT;
+		to.tv_nsec = 0;
+
+		tid = atomic_load(futex);
+		/* Kernel ignores futexes without the waiters flag */
+		tid |= FUTEX_WAITERS;
+		atomic_store(futex, tid);
+
+		ret = futex_wait((futex_t *) futex, tid, &to, 0);
+
+		/*
+		 * A real mutex_lock() implementation would loop here to finally
+		 * take the lock. We don't care about that, so we stop here.
+		 */
+	}
+
+	head->list_op_pending = NULL;
+
+	return ret;
+}
+
+/*
+ * This child thread will succeed taking the lock, and then will exit holding it
+ */
+static int child_fn_lock(void *arg)
+{
+	struct lock_struct *lock = (struct lock_struct *) arg;
+	struct robust_list_head head;
+	int ret;
+
+	ret = set_list(&head);
+	if (ret)
+		ksft_test_result_fail("set_robust_list error\n");
+
+	ret = mutex_lock(lock, &head, false);
+	if (ret)
+		ksft_test_result_fail("mutex_lock error\n");
+
+	pthread_barrier_wait(&barrier);
+
+	/*
+	 * There's a race here: the parent thread needs to be inside
+	 * futex_wait() before the child thread dies, otherwise it will miss the
+	 * wakeup from handle_futex_death() that this child will emit. We wait a
+	 * little bit just to make sure that this happens.
+	 */
+	sleep(1);
+
+	return 0;
+}
+
+/*
+ * Spawns a child thread that will set a robust list, take the lock, register it
+ * in the robust list and die. The parent thread will wait on this futex, and
+ * should be waken up when the child exits.
+ */
+static void test_robustness(void)
+{
+	struct lock_struct lock = { .futex = 0 };
+	struct robust_list_head head;
+	_Atomic(unsigned int) *futex = &lock.futex;
+	int ret;
+
+	ret = set_list(&head);
+	ASSERT_EQ(ret, 0);
+
+	/*
+	 * Lets use a barrier to ensure that the child thread takes the lock
+	 * before the parent
+	 */
+	ret = pthread_barrier_init(&barrier, NULL, 2);
+	ASSERT_EQ(ret, 0);
+
+	ret = create_child(&child_fn_lock, &lock);
+	ASSERT_NE(ret, -1);
+
+	pthread_barrier_wait(&barrier);
+	ret = mutex_lock(&lock, &head, false);
+
+	/*
+	 * futex_wait() should return 0 and the futex word should be marked with
+	 * FUTEX_OWNER_DIED
+	 */
+	ASSERT_EQ(ret, 0);
+	if (ret != 0)
+		printf("futex wait returned %d", errno);
+
+	ASSERT_TRUE(*futex | FUTEX_OWNER_DIED);
+
+	wait(NULL);
+	pthread_barrier_destroy(&barrier);
+
+	ksft_test_result_pass("%s\n", __func__);
+}
+
+/*
+ * The only valid value for len is sizeof(*head)
+ */
+static void test_set_robust_list_invalid_size(void)
+{
+	struct robust_list_head head;
+	size_t head_size = sizeof(struct robust_list_head);
+	int ret;
+
+	ret = set_robust_list(&head, head_size);
+	ASSERT_EQ(ret, 0);
+
+	ret = set_robust_list(&head, head_size * 2);
+	ASSERT_EQ(ret, -1);
+	ASSERT_EQ(errno, EINVAL);
+
+	ret = set_robust_list(&head, head_size - 1);
+	ASSERT_EQ(ret, -1);
+	ASSERT_EQ(errno, EINVAL);
+
+	ret = set_robust_list(&head, 0);
+	ASSERT_EQ(ret, -1);
+	ASSERT_EQ(errno, EINVAL);
+
+	ksft_test_result_pass("%s\n", __func__);
+}
+
+/*
+ * Test get_robust_list with pid = 0, getting the list of the running thread
+ */
+static void test_get_robust_list_self(void)
+{
+	struct robust_list_head head, head2, *get_head;
+	size_t head_size = sizeof(struct robust_list_head), len_ptr;
+	int ret;
+
+	ret = set_robust_list(&head, head_size);
+	ASSERT_EQ(ret, 0);
+
+	ret = get_robust_list(0, &get_head, &len_ptr);
+	ASSERT_EQ(ret, 0);
+	ASSERT_EQ(get_head, &head);
+	ASSERT_EQ(head_size, len_ptr);
+
+	ret = set_robust_list(&head2, head_size);
+	ASSERT_EQ(ret, 0);
+
+	ret = get_robust_list(0, &get_head, &len_ptr);
+	ASSERT_EQ(ret, 0);
+	ASSERT_EQ(get_head, &head2);
+	ASSERT_EQ(head_size, len_ptr);
+
+	ksft_test_result_pass("%s\n", __func__);
+}
+
+static int child_list(void *arg)
+{
+	struct robust_list_head *head = (struct robust_list_head *) arg;
+	int ret;
+
+	ret = set_robust_list(head, sizeof(struct robust_list_head));
+	if (ret)
+		ksft_test_result_fail("set_robust_list error\n");
+
+	pthread_barrier_wait(&barrier);
+	pthread_barrier_wait(&barrier2);
+
+	return 0;
+}
+
+/*
+ * Test get_robust_list from another thread. We use two barriers here to ensure
+ * that:
+ *   1) the child thread set the list before we try to get it from the
+ * parent
+ *   2) the child thread still alive when we try to get the list from it
+ */
+static void test_get_robust_list_child(void)
+{
+	pid_t tid;
+	int ret;
+	struct robust_list_head head, *get_head;
+	size_t len_ptr;
+
+	ret = pthread_barrier_init(&barrier, NULL, 2);
+	ret = pthread_barrier_init(&barrier2, NULL, 2);
+	ASSERT_EQ(ret, 0);
+
+	tid = create_child(&child_list, &head);
+	ASSERT_NE(tid, -1);
+
+	pthread_barrier_wait(&barrier);
+
+	ret = get_robust_list(tid, &get_head, &len_ptr);
+	ASSERT_EQ(ret, 0);
+	ASSERT_EQ(&head, get_head);
+
+	pthread_barrier_wait(&barrier2);
+
+	wait(NULL);
+	pthread_barrier_destroy(&barrier);
+	pthread_barrier_destroy(&barrier2);
+
+	ksft_test_result_pass("%s\n", __func__);
+}
+
+static int child_fn_lock_with_error(void *arg)
+{
+	struct lock_struct *lock = (struct lock_struct *) arg;
+	struct robust_list_head head;
+	int ret;
+
+	ret = set_list(&head);
+	if (ret)
+		ksft_test_result_fail("set_robust_list error\n");
+
+	ret = mutex_lock(lock, &head, true);
+	if (ret)
+		ksft_test_result_fail("mutex_lock error\n");
+
+	pthread_barrier_wait(&barrier);
+
+	sleep(1);
+
+	return 0;
+}
+
+/*
+ * Same as robustness test, but inject an error where the mutex_lock() exits
+ * earlier, just after setting list_op_pending and taking the lock, to test the
+ * list_op_pending mechanism
+ */
+static void test_set_list_op_pending(void)
+{
+	struct lock_struct lock = { .futex = 0 };
+	struct robust_list_head head;
+	_Atomic(unsigned int) *futex = &lock.futex;
+	int ret;
+
+	ret = set_list(&head);
+	ASSERT_EQ(ret, 0);
+
+	ret = pthread_barrier_init(&barrier, NULL, 2);
+	ASSERT_EQ(ret, 0);
+
+	ret = create_child(&child_fn_lock_with_error, &lock);
+	ASSERT_NE(ret, -1);
+
+	pthread_barrier_wait(&barrier);
+	ret = mutex_lock(&lock, &head, false);
+
+	ASSERT_EQ(ret, 0);
+	if (ret != 0)
+		printf("futex wait returned %d", errno);
+
+	ASSERT_TRUE(*futex | FUTEX_OWNER_DIED);
+
+	wait(NULL);
+	pthread_barrier_destroy(&barrier);
+
+	ksft_test_result_pass("%s\n", __func__);
+}
+
+#define CHILD_NR 10
+
+static int child_lock_holder(void *arg)
+{
+	struct lock_struct *locks = (struct lock_struct *) arg;
+	struct robust_list_head head;
+	int i;
+
+	set_list(&head);
+
+	for (i = 0; i < CHILD_NR; i++) {
+		locks[i].futex = 0;
+		mutex_lock(&locks[i], &head, false);
+	}
+
+	pthread_barrier_wait(&barrier);
+	pthread_barrier_wait(&barrier2);
+
+	sleep(1);
+	return 0;
+}
+
+static int child_wait_lock(void *arg)
+{
+	struct lock_struct *lock = (struct lock_struct *) arg;
+	struct robust_list_head head;
+	int ret;
+
+	pthread_barrier_wait(&barrier2);
+	ret = mutex_lock(lock, &head, false);
+
+	if (ret)
+		ksft_test_result_fail("mutex_lock error\n");
+
+	if (!(lock->futex | FUTEX_OWNER_DIED))
+		ksft_test_result_fail("futex not marked with FUTEX_OWNER_DIED\n");
+
+	return 0;
+}
+
+/*
+ * Test a robust list of more than one element. All the waiters should wake when
+ * the holder dies
+ */
+static void test_robust_list_multiple_elements(void)
+{
+	struct lock_struct locks[CHILD_NR];
+	int i, ret;
+
+	ret = pthread_barrier_init(&barrier, NULL, 2);
+	ASSERT_EQ(ret, 0);
+	ret = pthread_barrier_init(&barrier2, NULL, CHILD_NR + 1);
+	ASSERT_EQ(ret, 0);
+
+	create_child(&child_lock_holder, &locks);
+
+	/* Wait until the locker thread takes the look */
+	pthread_barrier_wait(&barrier);
+
+	for (i = 0; i < CHILD_NR; i++)
+		create_child(&child_wait_lock, &locks[i]);
+
+	/* Wait for all children to return */
+	while (wait(NULL) > 0);
+
+	pthread_barrier_destroy(&barrier);
+	pthread_barrier_destroy(&barrier2);
+
+	ksft_test_result_pass("%s\n", __func__);
+}
+
+static int child_circular_list(void *arg)
+{
+	static struct robust_list_head head;
+	struct lock_struct a, b, c;
+	int ret;
+
+	ret = set_list(&head);
+	if (ret)
+		ksft_test_result_fail("set_list error\n");
+
+	head.list.next = &a.list;
+
+	/*
+	 * The last element should point to head list, but we short circuit it
+	 */
+	a.list.next = &b.list;
+	b.list.next = &c.list;
+	c.list.next = &a.list;
+
+	return 0;
+}
+
+/*
+ * Create a circular robust list. The kernel should be able to destroy the list
+ * while processing it so it won't be trapped in an infinite loop while handling
+ * a process exit
+ */
+static void test_circular_list(void)
+{
+	create_child(child_circular_list, NULL);
+
+	wait(NULL);
+
+	ksft_test_result_pass("%s\n", __func__);
+}
+
+void usage(char *prog)
+{
+	printf("Usage: %s\n", prog);
+	printf("  -c	Use color\n");
+	printf("  -h	Display this help message\n");
+	printf("  -v L	Verbosity level: %d=QUIET %d=CRITICAL %d=INFO\n",
+	       VQUIET, VCRITICAL, VINFO);
+}
+
+int main(int argc, char *argv[])
+{
+	int c;
+
+	while ((c = getopt(argc, argv, "cht:v:")) != -1) {
+		switch (c) {
+		case 'c':
+			log_color(1);
+			break;
+		case 'h':
+			usage(basename(argv[0]));
+			exit(0);
+		case 'v':
+			log_verbosity(atoi(optarg));
+			break;
+		default:
+			usage(basename(argv[0]));
+			exit(1);
+		}
+	}
+
+	ksft_print_header();
+	ksft_set_plan(7);
+
+	test_robustness();
+
+	test_set_robust_list_invalid_size();
+	test_get_robust_list_self();
+	test_get_robust_list_child();
+	test_set_list_op_pending();
+	test_robust_list_multiple_elements();
+	test_circular_list();
+
+	ksft_print_cnts();
+	return 0;
+}

-- 
2.49.0

[PATCH RESEND v4 3/7] futex: Use explicit sizes for compat_exit_robust_list

[André Almeida]

There are two functions for handling robust lists during the task
exit: exit_robust_list() and compat_exit_robust_list(). The first one
handles either 64bit or 32bit lists, depending if it's a 64bit or 32bit
kernel. The compat_exit_robust_list() only exists in 64bit kernels that
supports 32bit syscalls, and handles 32bit lists.

For the new syscall set_robust_list2(), 64bit kernels need to be able to
handle 32bit lists despite having or not support for 32bit syscalls, so
make compat_exit_robust_list() exist regardless of compat_ config.

Also, use explicitly sizing, otherwise in a 32bit kernel both
exit_robust_list() and compat_exit_robust_list() would be the exactly
same function, with none of them dealing with 64bit robust lists.

Signed-off-by: André Almeida <andrealmeid@igalia.com>
---
 include/linux/compat.h  | 12 +-----------
 include/linux/futex.h   | 11 +++++++++++
 include/linux/sched.h   |  2 +-
 kernel/futex/core.c     | 44 ++++++++++++++++++++++++++++----------------
 kernel/futex/syscalls.c |  4 ++--
 5 files changed, 43 insertions(+), 30 deletions(-)

diff --git a/include/linux/compat.h b/include/linux/compat.h
index 56cebaff0c910fda853a0e2b3d6d0517e55f8b38..968a9135ff486cf9c8be2a18b80cd4c46e890236 100644
--- a/include/linux/compat.h
+++ b/include/linux/compat.h
@@ -385,16 +385,6 @@ struct compat_ifconf {
 	compat_caddr_t  ifcbuf;
 };
 
-struct compat_robust_list {
-	compat_uptr_t			next;
-};
-
-struct compat_robust_list_head {
-	struct compat_robust_list	list;
-	compat_long_t			futex_offset;
-	compat_uptr_t			list_op_pending;
-};
-
 #ifdef CONFIG_COMPAT_OLD_SIGACTION
 struct compat_old_sigaction {
 	compat_uptr_t			sa_handler;
@@ -672,7 +662,7 @@ asmlinkage long compat_sys_waitid(int, compat_pid_t,
 		struct compat_siginfo __user *, int,
 		struct compat_rusage __user *);
 asmlinkage long
-compat_sys_set_robust_list(struct compat_robust_list_head __user *head,
+compat_sys_set_robust_list(struct robust_list_head32 __user *head,
 			   compat_size_t len);
 asmlinkage long
 compat_sys_get_robust_list(int pid, compat_uptr_t __user *head_ptr,
diff --git a/include/linux/futex.h b/include/linux/futex.h
index 168ffd5996b4808491c05bdc7c8d0aeca1d37ee5..cd7c5d12c846566c56f3f3ea74b95e437a6e8193 100644
--- a/include/linux/futex.h
+++ b/include/linux/futex.h
@@ -56,6 +56,17 @@ union futex_key {
 #define FUTEX_KEY_INIT (union futex_key) { .both = { .ptr = 0ULL } }
 
 #ifdef CONFIG_FUTEX
+
+struct robust_list32 {
+	u32 next;
+};
+
+struct robust_list_head32 {
+	struct robust_list32	list;
+	s32			futex_offset;
+	u32			list_op_pending;
+};
+
 enum {
 	FUTEX_STATE_OK,
 	FUTEX_STATE_EXITING,
diff --git a/include/linux/sched.h b/include/linux/sched.h
index 45e5953b8f326c2ff5e19de469d6cba27cc4c17d..51e5d05a9fcd407dcd53b7b7cb8c59783660a826 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -1324,7 +1324,7 @@ struct task_struct {
 #ifdef CONFIG_FUTEX
 	struct robust_list_head __user	*robust_list;
 #ifdef CONFIG_COMPAT
-	struct compat_robust_list_head __user *compat_robust_list;
+	struct robust_list_head32 __user *compat_robust_list;
 #endif
 	struct list_head		pi_state_list;
 	struct futex_pi_state		*pi_state_cache;
diff --git a/kernel/futex/core.c b/kernel/futex/core.c
index 19a2c65f3d373c0b60c864a6fe0604787221d342..8640770aadc611b7341a3abb41bdb740e6394479 100644
--- a/kernel/futex/core.c
+++ b/kernel/futex/core.c
@@ -1144,13 +1144,14 @@ static inline int fetch_robust_entry(struct robust_list __user **entry,
 	return 0;
 }
 
+#ifdef CONFIG_64BIT
 /*
  * Walk curr->robust_list (very carefully, it's a userspace list!)
  * and mark any locks found there dead, and notify any waiters.
  *
  * We silently return on any sign of list-walking problem.
  */
-static void exit_robust_list(struct task_struct *curr)
+static void exit_robust_list64(struct task_struct *curr)
 {
 	struct robust_list_head __user *head = curr->robust_list;
 	struct robust_list __user *entry, *next_entry, *pending;
@@ -1211,8 +1212,13 @@ static void exit_robust_list(struct task_struct *curr)
 				   curr, pip, HANDLE_DEATH_PENDING);
 	}
 }
+#else
+static void exit_robust_list64(struct task_struct *curr)
+{
+	pr_warn("32bit kernel should not allow ROBUST_LIST_64BIT");
+}
+#endif
 
-#ifdef CONFIG_COMPAT
 static void __user *futex_uaddr(struct robust_list __user *entry,
 				compat_long_t futex_offset)
 {
@@ -1226,13 +1232,13 @@ static void __user *futex_uaddr(struct robust_list __user *entry,
  * Fetch a robust-list pointer. Bit 0 signals PI futexes:
  */
 static inline int
-compat_fetch_robust_entry(compat_uptr_t *uentry, struct robust_list __user **entry,
-		   compat_uptr_t __user *head, unsigned int *pi)
+fetch_robust_entry32(u32 *uentry, struct robust_list __user **entry,
+		     u32 __user *head, unsigned int *pi)
 {
 	if (get_user(*uentry, head))
 		return -EFAULT;
 
-	*entry = compat_ptr((*uentry) & ~1);
+	*entry = (void __user *)(unsigned long)((*uentry) & ~1);
 	*pi = (unsigned int)(*uentry) & 1;
 
 	return 0;
@@ -1244,21 +1250,21 @@ compat_fetch_robust_entry(compat_uptr_t *uentry, struct robust_list __user **ent
  *
  * We silently return on any sign of list-walking problem.
  */
-static void compat_exit_robust_list(struct task_struct *curr)
+static void exit_robust_list32(struct task_struct *curr)
 {
-	struct compat_robust_list_head __user *head = curr->compat_robust_list;
+	struct robust_list_head32 __user *head = curr->compat_robust_list;
 	struct robust_list __user *entry, *next_entry, *pending;
 	unsigned int limit = ROBUST_LIST_LIMIT, pi, pip;
 	unsigned int next_pi;
-	compat_uptr_t uentry, next_uentry, upending;
-	compat_long_t futex_offset;
+	u32 uentry, next_uentry, upending;
+	s32 futex_offset;
 	int rc;
 
 	/*
 	 * Fetch the list head (which was registered earlier, via
 	 * sys_set_robust_list()):
 	 */
-	if (compat_fetch_robust_entry(&uentry, &entry, &head->list.next, &pi))
+	if (fetch_robust_entry32((u32 *)&uentry, &entry, (u32 *)&head->list.next, &pi))
 		return;
 	/*
 	 * Fetch the relative futex offset:
@@ -1269,7 +1275,7 @@ static void compat_exit_robust_list(struct task_struct *curr)
 	 * Fetch any possibly pending lock-add first, and handle it
 	 * if it exists:
 	 */
-	if (compat_fetch_robust_entry(&upending, &pending,
+	if (fetch_robust_entry32(&upending, &pending,
 			       &head->list_op_pending, &pip))
 		return;
 
@@ -1279,8 +1285,8 @@ static void compat_exit_robust_list(struct task_struct *curr)
 		 * Fetch the next entry in the list before calling
 		 * handle_futex_death:
 		 */
-		rc = compat_fetch_robust_entry(&next_uentry, &next_entry,
-			(compat_uptr_t __user *)&entry->next, &next_pi);
+		rc = fetch_robust_entry32(&next_uentry, &next_entry,
+			(u32 __user *)&entry->next, &next_pi);
 		/*
 		 * A pending lock might already be on the list, so
 		 * dont process it twice:
@@ -1311,7 +1317,6 @@ static void compat_exit_robust_list(struct task_struct *curr)
 		handle_futex_death(uaddr, curr, pip, HANDLE_DEATH_PENDING);
 	}
 }
-#endif
 
 #ifdef CONFIG_FUTEX_PI
 
@@ -1406,14 +1411,21 @@ static inline void exit_pi_state_list(struct task_struct *curr) { }
 
 static void futex_cleanup(struct task_struct *tsk)
 {
+#ifdef CONFIG_64BIT
 	if (unlikely(tsk->robust_list)) {
-		exit_robust_list(tsk);
+		exit_robust_list64(tsk);
 		tsk->robust_list = NULL;
 	}
+#else
+	if (unlikely(tsk->robust_list)) {
+		exit_robust_list32(tsk);
+		tsk->robust_list = NULL;
+	}
+#endif
 
 #ifdef CONFIG_COMPAT
 	if (unlikely(tsk->compat_robust_list)) {
-		compat_exit_robust_list(tsk);
+		exit_robust_list32(tsk);
 		tsk->compat_robust_list = NULL;
 	}
 #endif
diff --git a/kernel/futex/syscalls.c b/kernel/futex/syscalls.c
index 4b6da9116aa6c33db9796e3055ce0c90b02d7b91..dba193dfd216cc929c8f4d979aa2bcd99237e2d8 100644
--- a/kernel/futex/syscalls.c
+++ b/kernel/futex/syscalls.c
@@ -440,7 +440,7 @@ SYSCALL_DEFINE4(futex_requeue,
 
 #ifdef CONFIG_COMPAT
 COMPAT_SYSCALL_DEFINE2(set_robust_list,
-		struct compat_robust_list_head __user *, head,
+		struct robust_list_head32 __user *, head,
 		compat_size_t, len)
 {
 	if (unlikely(len != sizeof(*head)))
@@ -455,7 +455,7 @@ COMPAT_SYSCALL_DEFINE3(get_robust_list, int, pid,
 			compat_uptr_t __user *, head_ptr,
 			compat_size_t __user *, len_ptr)
 {
-	struct compat_robust_list_head __user *head;
+	struct robust_list_head32 __user *head;
 	unsigned long ret;
 	struct task_struct *p;
 

-- 
2.49.0

[PATCH RESEND v4 4/7] futex: Create set_robust_list2

[André Almeida]

Create a new robust_list() syscall. The current syscall can't be
expanded to cover the following use case, so a new one is needed. This
new syscall allows users to set multiple robust lists per process and to
have either 32bit or 64bit pointers in the list.

* Interface

This is the proposed interface:

	long set_robust_list2(void *head, int index, unsigned int flags)

`head` is the head of the userspace struct robust_list_head, just as old
set_robust_list(). It needs to be a void pointer since it can point to a
normal robust_list_head or a compat_robust_list_head.

`flags` can be used for defining the list type:

	enum robust_list_type {
	 	ROBUST_LIST_32BIT,
		ROBUST_LIST_64BIT,
	 };

`index` is the index in the internal robust_list's linked list (the
naming starts to get confusing, I reckon). If `index == -1`, that means
that user wants to set a new robust_list, and the kernel will append it
in the end of the list, assign a new index and return this index to the
user. If `index >= 0`, that means that user wants to re-set `*head` of
an already existing list (similarly to what happens when you call
set_robust_list() twice with different `*head`).

If `index` is out of range, or it points to a non-existing robust_list,
or if the internal list is full, an error is returned.

Unaligned `head` addresses are refused by the kernel with -EINVAL.

User cannot remove lists.

* Implementation

The old syscall's set/get_robust_list() are converted to use the linked
list as well. When using only the old syscalls user shouldn't any
difference as the internal code will handle the linked list insertion as
usual. When mixing old and new interfaces users should be aware that one
of the elements of the list was created by another syscall and they
should have special care handling this element index.

On exit, the linked list is parsed and all robust lists regardless of
which interface it was used to create them are handled.

Signed-off-by: André Almeida <andrealmeid@igalia.com>
---
 include/linux/futex.h             |   5 +-
 include/linux/sched.h             |   5 +-
 include/uapi/asm-generic/unistd.h |   2 +
 include/uapi/linux/futex.h        |  24 +++++++++
 kernel/futex/core.c               | 111 ++++++++++++++++++++++++++++++--------
 kernel/futex/futex.h              |   5 ++
 kernel/futex/syscalls.c           |  81 ++++++++++++++++++++++++++--
 7 files changed, 204 insertions(+), 29 deletions(-)

diff --git a/include/linux/futex.h b/include/linux/futex.h
index cd7c5d12c846566c56f3f3ea74b95e437a6e8193..7721629926535c775bd7b05b5283a3d0b51262d6 100644
--- a/include/linux/futex.h
+++ b/include/linux/futex.h
@@ -75,10 +75,11 @@ enum {
 
 static inline void futex_init_task(struct task_struct *tsk)
 {
-	tsk->robust_list = NULL;
+	tsk->robust_list_index = -1;
 #ifdef CONFIG_COMPAT
-	tsk->compat_robust_list = NULL;
+	tsk->compat_robust_list_index = -1;
 #endif
+	INIT_LIST_HEAD(&tsk->robust_list2);
 	INIT_LIST_HEAD(&tsk->pi_state_list);
 	tsk->pi_state_cache = NULL;
 	tsk->futex_state = FUTEX_STATE_OK;
diff --git a/include/linux/sched.h b/include/linux/sched.h
index 51e5d05a9fcd407dcd53b7b7cb8c59783660a826..a37c55cf0a4d942ec1fbedb8bcd4be5a3ebb20bb 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -1322,10 +1322,11 @@ struct task_struct {
 	u32				rmid;
 #endif
 #ifdef CONFIG_FUTEX
-	struct robust_list_head __user	*robust_list;
+	int				robust_list_index;
 #ifdef CONFIG_COMPAT
-	struct robust_list_head32 __user *compat_robust_list;
+	int				compat_robust_list_index;
 #endif
+	struct list_head		robust_list2;
 	struct list_head		pi_state_list;
 	struct futex_pi_state		*pi_state_cache;
 	struct mutex			futex_exit_mutex;
diff --git a/include/uapi/asm-generic/unistd.h b/include/uapi/asm-generic/unistd.h
index 2892a45023af6d3eb941623d4fed04841ab07e02..ebe68c2c88eb5390dda184ce9268a8d3a606c9e5 100644
--- a/include/uapi/asm-generic/unistd.h
+++ b/include/uapi/asm-generic/unistd.h
@@ -852,6 +852,8 @@ __SYSCALL(__NR_removexattrat, sys_removexattrat)
 #define __NR_open_tree_attr 467
 __SYSCALL(__NR_open_tree_attr, sys_open_tree_attr)
 
+#define __NR_set_robust_list2 467
+
 #undef __NR_syscalls
 #define __NR_syscalls 468
 
diff --git a/include/uapi/linux/futex.h b/include/uapi/linux/futex.h
index 7e2744ec89336a260e89883e95222eda199eeb7f..cbd321eca03afb6bdcf47e9534761d82f9de7e43 100644
--- a/include/uapi/linux/futex.h
+++ b/include/uapi/linux/futex.h
@@ -153,6 +153,30 @@ struct robust_list_head {
 	struct robust_list __user *list_op_pending;
 };
 
+#define ROBUST_LISTS_PER_TASK 10
+
+enum robust_list2_type {
+	ROBUST_LIST_32BIT,
+	ROBUST_LIST_64BIT,
+};
+
+#define ROBUST_LIST_TYPE_MASK (ROBUST_LIST_32BIT | ROBUST_LIST_64BIT)
+
+/*
+ * This is an entry of a linked list of robust lists.
+ *
+ * @head: can point to a 64bit list or a 32bit list
+ * @list_type: determine the size of the futex pointers in the list
+ * @index: the index of this entry in the list
+ * @list: linked list element
+ */
+struct robust_list2_entry {
+	void __user *head;
+	enum robust_list2_type list_type;
+	unsigned int index;
+	struct list_head list;
+};
+
 /*
  * Are there any waiters for this robust futex:
  */
diff --git a/kernel/futex/core.c b/kernel/futex/core.c
index 8640770aadc611b7341a3abb41bdb740e6394479..49b3bc592948a811f995017027f33ad8f285531f 100644
--- a/kernel/futex/core.c
+++ b/kernel/futex/core.c
@@ -1151,9 +1151,9 @@ static inline int fetch_robust_entry(struct robust_list __user **entry,
  *
  * We silently return on any sign of list-walking problem.
  */
-static void exit_robust_list64(struct task_struct *curr)
+static void exit_robust_list64(struct task_struct *curr,
+			       struct robust_list_head __user *head)
 {
-	struct robust_list_head __user *head = curr->robust_list;
 	struct robust_list __user *entry, *next_entry, *pending;
 	unsigned int limit = ROBUST_LIST_LIMIT, pi, pip;
 	unsigned int next_pi;
@@ -1213,7 +1213,8 @@ static void exit_robust_list64(struct task_struct *curr)
 	}
 }
 #else
-static void exit_robust_list64(struct task_struct *curr)
+static void exit_robust_list64(struct task_struct *curr,
+			      struct robust_list_head __user *head)
 {
 	pr_warn("32bit kernel should not allow ROBUST_LIST_64BIT");
 }
@@ -1250,9 +1251,9 @@ fetch_robust_entry32(u32 *uentry, struct robust_list __user **entry,
  *
  * We silently return on any sign of list-walking problem.
  */
-static void exit_robust_list32(struct task_struct *curr)
+static void exit_robust_list32(struct task_struct *curr,
+			       struct robust_list_head32 __user *head)
 {
-	struct robust_list_head32 __user *head = curr->compat_robust_list;
 	struct robust_list __user *entry, *next_entry, *pending;
 	unsigned int limit = ROBUST_LIST_LIMIT, pi, pip;
 	unsigned int next_pi;
@@ -1318,6 +1319,70 @@ static void exit_robust_list32(struct task_struct *curr)
 	}
 }
 
+long do_set_robust_list2(struct robust_list_head __user *head,
+			 int index, unsigned int type)
+{
+	struct list_head *list2 = &current->robust_list2;
+	struct robust_list2_entry *prev, *new = NULL;
+
+	if (index == -1) {
+		if (list_empty(list2)) {
+			index = 0;
+		} else {
+			prev = list_last_entry(list2, struct robust_list2_entry, list);
+			index = prev->index + 1;
+		}
+
+		if (index >= ROBUST_LISTS_PER_TASK)
+			return -EINVAL;
+
+		new = kmalloc(sizeof(struct robust_list2_entry), GFP_KERNEL);
+		if (!new)
+			return -ENOMEM;
+
+		list_add_tail(&new->list, list2);
+		new->index = index;
+
+	} else if (index >= 0) {
+		struct robust_list2_entry *curr;
+
+		if (list_empty(list2))
+			return -ENOENT;
+
+		list_for_each_entry(curr, list2, list) {
+			if (index == curr->index) {
+				new = curr;
+				break;
+			}
+		}
+
+		if (!new)
+			return -ENOENT;
+	}
+
+	BUG_ON(!new);
+	new->head = head;
+	new->list_type = type;
+
+	return index;
+}
+
+struct robust_list_head __user *get_robust_list2(int index, struct task_struct *task)
+{
+	struct list_head *list2 = &task->robust_list2;
+	struct robust_list2_entry *curr;
+
+	if (list_empty(list2) || index == -1)
+		return NULL;
+
+	list_for_each_entry(curr, list2, list) {
+		if (index == curr->index)
+			return curr->head;
+	}
+
+	return NULL;
+}
+
 #ifdef CONFIG_FUTEX_PI
 
 /*
@@ -1411,24 +1476,28 @@ static inline void exit_pi_state_list(struct task_struct *curr) { }
 
 static void futex_cleanup(struct task_struct *tsk)
 {
-#ifdef CONFIG_64BIT
-	if (unlikely(tsk->robust_list)) {
-		exit_robust_list64(tsk);
-		tsk->robust_list = NULL;
-	}
-#else
-	if (unlikely(tsk->robust_list)) {
-		exit_robust_list32(tsk);
-		tsk->robust_list = NULL;
-	}
-#endif
+	struct robust_list2_entry *curr, *n;
+	struct list_head *list2 = &tsk->robust_list2;
 
-#ifdef CONFIG_COMPAT
-	if (unlikely(tsk->compat_robust_list)) {
-		exit_robust_list32(tsk);
-		tsk->compat_robust_list = NULL;
+	/*
+	 * Walk through the linked list, parsing robust lists and freeing the
+	 * allocated lists
+	 */
+	if (unlikely(!list_empty(list2))) {
+		list_for_each_entry_safe(curr, n, list2, list) {
+			if (curr->head != NULL) {
+				if (curr->list_type == ROBUST_LIST_64BIT)
+					exit_robust_list64(tsk, curr->head);
+				else if (curr->list_type == ROBUST_LIST_32BIT)
+					exit_robust_list32(tsk, curr->head);
+				curr->head = NULL;
+			}
+			list_del_init(&curr->list);
+			kfree(curr);
+		}
 	}
-#endif
+
+	tsk->robust_list_index = -1;
 
 	if (unlikely(!list_empty(&tsk->pi_state_list)))
 		exit_pi_state_list(tsk);
diff --git a/kernel/futex/futex.h b/kernel/futex/futex.h
index fcd1617212eed0e3c2367d2b463a0e019eda6d13..67201e51fa1798a21ff68f60b1e35977b9bd267b 100644
--- a/kernel/futex/futex.h
+++ b/kernel/futex/futex.h
@@ -467,6 +467,11 @@ extern int __futex_wait(u32 __user *uaddr, unsigned int flags, u32 val,
 extern int futex_wait(u32 __user *uaddr, unsigned int flags, u32 val,
 		      ktime_t *abs_time, u32 bitset);
 
+extern long do_set_robust_list2(struct robust_list_head __user *head,
+			 int index, unsigned int type);
+
+extern struct robust_list_head __user *get_robust_list2(int index, struct task_struct *task);
+
 /**
  * struct futex_vector - Auxiliary struct for futex_waitv()
  * @w: Userspace provided data
diff --git a/kernel/futex/syscalls.c b/kernel/futex/syscalls.c
index dba193dfd216cc929c8f4d979aa2bcd99237e2d8..56ee1123cbd8ea26c8d22aa74e5faed2974ec577 100644
--- a/kernel/futex/syscalls.c
+++ b/kernel/futex/syscalls.c
@@ -20,6 +20,18 @@
  * the list. There can only be one such pending lock.
  */
 
+#ifdef CONFIG_64BIT
+static inline int robust_list_native_type(void)
+{
+	return ROBUST_LIST_64BIT;
+}
+#else
+static inline int robust_list_native_type(void)
+{
+	return ROBUST_LIST_32BIT;
+}
+#endif
+
 /**
  * sys_set_robust_list() - Set the robust-futex list head of a task
  * @head:	pointer to the list-head
@@ -28,17 +40,63 @@
 SYSCALL_DEFINE2(set_robust_list, struct robust_list_head __user *, head,
 		size_t, len)
 {
+	unsigned int type = robust_list_native_type();
+	int ret;
+
 	/*
 	 * The kernel knows only one size for now:
 	 */
 	if (unlikely(len != sizeof(*head)))
 		return -EINVAL;
 
-	current->robust_list = head;
+	ret = do_set_robust_list2(head, current->robust_list_index, type);
+	if (ret < 0)
+		return ret;
+
+	current->robust_list_index = ret;
 
 	return 0;
 }
 
+#define ROBUST_LIST_FLAGS ROBUST_LIST_TYPE_MASK
+
+/*
+ * sys_set_robust_list2()
+ *
+ * When index == -1, create a new list for user. When index >= 0, try to find
+ * the corresponding list and re-set the head there.
+ *
+ * Return values:
+ *  >= 0: success, index of the robust list
+ *  -EINVAL: invalid flags, invalid index
+ *  -ENOENT: requested index no where to be found
+ *  -ENOMEM: error allocating new list
+ *  -ESRCH: too many allocated lists
+ */
+SYSCALL_DEFINE3(set_robust_list2, struct robust_list_head __user *, head,
+		int, index, unsigned int, flags)
+{
+	unsigned int type;
+
+	type = flags & ROBUST_LIST_TYPE_MASK;
+
+	if (index < -1 || index >= ROBUST_LISTS_PER_TASK)
+		return -EINVAL;
+
+	if ((flags & ~ROBUST_LIST_FLAGS) != 0)
+		return -EINVAL;
+
+	if (((uintptr_t) head % sizeof(u32)) != 0)
+		return -EINVAL;
+
+#ifndef CONFIG_64BIT
+	if (type == ROBUST_LIST_64BIT)
+		return -EINVAL;
+#endif
+
+	return do_set_robust_list2(head, index, type);
+}
+
 /**
  * sys_get_robust_list() - Get the robust-futex list head of a task
  * @pid:	pid of the process [zero for current task]
@@ -52,6 +110,7 @@ SYSCALL_DEFINE3(get_robust_list, int, pid,
 	struct robust_list_head __user *head;
 	unsigned long ret;
 	struct task_struct *p;
+	int index;
 
 	rcu_read_lock();
 
@@ -68,9 +127,11 @@ SYSCALL_DEFINE3(get_robust_list, int, pid,
 	if (!ptrace_may_access(p, PTRACE_MODE_READ_REALCREDS))
 		goto err_unlock;
 
-	head = p->robust_list;
+	index = p->robust_list_index;
 	rcu_read_unlock();
 
+	head = get_robust_list2(index, p);
+
 	if (put_user(sizeof(*head), len_ptr))
 		return -EFAULT;
 	return put_user(head, head_ptr);
@@ -443,10 +504,19 @@ COMPAT_SYSCALL_DEFINE2(set_robust_list,
 		struct robust_list_head32 __user *, head,
 		compat_size_t, len)
 {
+	unsigned int type = ROBUST_LIST_32BIT;
+	int ret;
+
 	if (unlikely(len != sizeof(*head)))
 		return -EINVAL;
 
-	current->compat_robust_list = head;
+	ret = do_set_robust_list2((struct robust_list_head __user *) head,
+				  current->robust_list_index, type);
+	if (ret < 0)
+		return ret;
+
+	current->robust_list_index = ret;
+
 
 	return 0;
 }
@@ -458,6 +528,7 @@ COMPAT_SYSCALL_DEFINE3(get_robust_list, int, pid,
 	struct robust_list_head32 __user *head;
 	unsigned long ret;
 	struct task_struct *p;
+	int index;
 
 	rcu_read_lock();
 
@@ -474,9 +545,11 @@ COMPAT_SYSCALL_DEFINE3(get_robust_list, int, pid,
 	if (!ptrace_may_access(p, PTRACE_MODE_READ_REALCREDS))
 		goto err_unlock;
 
-	head = p->compat_robust_list;
+	index = p->compat_robust_list_index;
 	rcu_read_unlock();
 
+	head = (struct robust_list_head32 __user *) get_robust_list2(index, p);
+
 	if (put_user(sizeof(*head), len_ptr))
 		return -EFAULT;
 	return put_user(ptr_to_compat(head), head_ptr);

-- 
2.49.0

[PATCH RESEND v4 5/7] futex: Wire up set_robust_list2 syscall

[André Almeida]

Wire up the new set_robust_list2 syscall in all available architectures.

Signed-off-by: André Almeida <andrealmeid@igalia.com>
---
 arch/alpha/kernel/syscalls/syscall.tbl      | 1 +
 arch/arm/tools/syscall.tbl                  | 1 +
 arch/m68k/kernel/syscalls/syscall.tbl       | 1 +
 arch/microblaze/kernel/syscalls/syscall.tbl | 1 +
 arch/mips/kernel/syscalls/syscall_n32.tbl   | 1 +
 arch/mips/kernel/syscalls/syscall_n64.tbl   | 1 +
 arch/mips/kernel/syscalls/syscall_o32.tbl   | 1 +
 arch/parisc/kernel/syscalls/syscall.tbl     | 1 +
 arch/powerpc/kernel/syscalls/syscall.tbl    | 1 +
 arch/s390/kernel/syscalls/syscall.tbl       | 1 +
 arch/sh/kernel/syscalls/syscall.tbl         | 1 +
 arch/sparc/kernel/syscalls/syscall.tbl      | 1 +
 arch/x86/entry/syscalls/syscall_32.tbl      | 1 +
 arch/x86/entry/syscalls/syscall_64.tbl      | 1 +
 arch/xtensa/kernel/syscalls/syscall.tbl     | 1 +
 kernel/sys_ni.c                             | 1 +
 scripts/syscall.tbl                         | 1 +
 17 files changed, 17 insertions(+)

diff --git a/arch/alpha/kernel/syscalls/syscall.tbl b/arch/alpha/kernel/syscalls/syscall.tbl
index 2dd6340de6b4efddc406f0c235701c15cf02f650..aecc167ac7706d25da73db8099f0813e268b820c 100644
--- a/arch/alpha/kernel/syscalls/syscall.tbl
+++ b/arch/alpha/kernel/syscalls/syscall.tbl
@@ -507,3 +507,4 @@
 575	common	listxattrat			sys_listxattrat
 576	common	removexattrat			sys_removexattrat
 577	common	open_tree_attr			sys_open_tree_attr
+578	common	set_robust_list2		sys_robust_list2
diff --git a/arch/arm/tools/syscall.tbl b/arch/arm/tools/syscall.tbl
index 27c1d5ebcd91c8c296dc6676307f66bfdf4ab78d..2e47ae5dc9a426d8e5e9dacf29caa54223cf2f5a 100644
--- a/arch/arm/tools/syscall.tbl
+++ b/arch/arm/tools/syscall.tbl
@@ -482,3 +482,4 @@
 465	common	listxattrat			sys_listxattrat
 466	common	removexattrat			sys_removexattrat
 467	common	open_tree_attr			sys_open_tree_attr
+468	common	set_robust_list2		sys_set_robust_list2
diff --git a/arch/m68k/kernel/syscalls/syscall.tbl b/arch/m68k/kernel/syscalls/syscall.tbl
index 9fe47112c586f152662af38a9a7f90957cb96cf8..7bcc8cc628c80a44fea2b53d5c69ab5e5f10a1d2 100644
--- a/arch/m68k/kernel/syscalls/syscall.tbl
+++ b/arch/m68k/kernel/syscalls/syscall.tbl
@@ -467,3 +467,4 @@
 465	common	listxattrat			sys_listxattrat
 466	common	removexattrat			sys_removexattrat
 467	common	open_tree_attr			sys_open_tree_attr
+468	common  set_robust_list2		sys_set_robust_list2
diff --git a/arch/microblaze/kernel/syscalls/syscall.tbl b/arch/microblaze/kernel/syscalls/syscall.tbl
index 7b6e97828e552d4da90046ddfcd4a55723e522bb..cd23608afe7e7dadfbf8e21df0486b85bfcb99ce 100644
--- a/arch/microblaze/kernel/syscalls/syscall.tbl
+++ b/arch/microblaze/kernel/syscalls/syscall.tbl
@@ -473,3 +473,4 @@
 465	common	listxattrat			sys_listxattrat
 466	common	removexattrat			sys_removexattrat
 467	common	open_tree_attr			sys_open_tree_attr
+468	common	set_robust_list2		sys_set_robust_list2
diff --git a/arch/mips/kernel/syscalls/syscall_n32.tbl b/arch/mips/kernel/syscalls/syscall_n32.tbl
index aa70e371bb54ab5d9c8dd8923b6ecf9693ee914d..0a31452ef6ed8fee8f1e2ead5d44acfbbe275fe9 100644
--- a/arch/mips/kernel/syscalls/syscall_n32.tbl
+++ b/arch/mips/kernel/syscalls/syscall_n32.tbl
@@ -406,3 +406,4 @@
 465	n32	listxattrat			sys_listxattrat
 466	n32	removexattrat			sys_removexattrat
 467	n32	open_tree_attr			sys_open_tree_attr
+468	n32	set_robust_list2		sys_set_robust_list2
diff --git a/arch/mips/kernel/syscalls/syscall_n64.tbl b/arch/mips/kernel/syscalls/syscall_n64.tbl
index 1e8c44c7b61492eabf00c777831e457a7a6e579c..4cb5a72256338f6fb407f940f1883d523113d609 100644
--- a/arch/mips/kernel/syscalls/syscall_n64.tbl
+++ b/arch/mips/kernel/syscalls/syscall_n64.tbl
@@ -382,3 +382,4 @@
 465	n64	listxattrat			sys_listxattrat
 466	n64	removexattrat			sys_removexattrat
 467	n64	open_tree_attr			sys_open_tree_attr
+468	n64	set_robust_list2		sys_set_robust_list2
diff --git a/arch/mips/kernel/syscalls/syscall_o32.tbl b/arch/mips/kernel/syscalls/syscall_o32.tbl
index 114a5a1a62302e32dd74d1679ff423a2d57c3c6b..c46238e9edd00d2861edcfa87c5ce7a62bfdc3d4 100644
--- a/arch/mips/kernel/syscalls/syscall_o32.tbl
+++ b/arch/mips/kernel/syscalls/syscall_o32.tbl
@@ -455,3 +455,4 @@
 465	o32	listxattrat			sys_listxattrat
 466	o32	removexattrat			sys_removexattrat
 467	o32	open_tree_attr			sys_open_tree_attr
+468	o32	set_robust_list2		sys_set_robust_list2
diff --git a/arch/parisc/kernel/syscalls/syscall.tbl b/arch/parisc/kernel/syscalls/syscall.tbl
index 94df3cb957e9d547d192e8732c0cf23ef2b5ce5d..71071489a18375013bbfbe26578a634283c1e07b 100644
--- a/arch/parisc/kernel/syscalls/syscall.tbl
+++ b/arch/parisc/kernel/syscalls/syscall.tbl
@@ -466,3 +466,4 @@
 465	common	listxattrat			sys_listxattrat
 466	common	removexattrat			sys_removexattrat
 467	common	open_tree_attr			sys_open_tree_attr
+468	common	set_robust_list2		sys_set_robust_list2
diff --git a/arch/powerpc/kernel/syscalls/syscall.tbl b/arch/powerpc/kernel/syscalls/syscall.tbl
index 9a084bdb892694bc562f514b55212d167cbac12f..edc4d0bef3f1c7ab826ea8180e7f5ceba4774c07 100644
--- a/arch/powerpc/kernel/syscalls/syscall.tbl
+++ b/arch/powerpc/kernel/syscalls/syscall.tbl
@@ -558,3 +558,4 @@
 465	common	listxattrat			sys_listxattrat
 466	common	removexattrat			sys_removexattrat
 467	common	open_tree_attr			sys_open_tree_attr
+468	common	set_robust_list2		sys_set_robust_list2
diff --git a/arch/s390/kernel/syscalls/syscall.tbl b/arch/s390/kernel/syscalls/syscall.tbl
index a4569b96ef06c54ce7aa795d039541c90a38284f..ff8c594073ec8c3486cc61544d14a338d3f3a906 100644
--- a/arch/s390/kernel/syscalls/syscall.tbl
+++ b/arch/s390/kernel/syscalls/syscall.tbl
@@ -470,3 +470,4 @@
 465  common	listxattrat		sys_listxattrat			sys_listxattrat
 466  common	removexattrat		sys_removexattrat		sys_removexattrat
 467  common	open_tree_attr		sys_open_tree_attr		sys_open_tree_attr
+468  common	set_robust_list2	sys_set_robust_list2		sys_set_robust_list2
diff --git a/arch/sh/kernel/syscalls/syscall.tbl b/arch/sh/kernel/syscalls/syscall.tbl
index 52a7652fcff6394b96ace1f3b0ed72250ee5e669..507789194570a9e7b492b210be30bb41021be289 100644
--- a/arch/sh/kernel/syscalls/syscall.tbl
+++ b/arch/sh/kernel/syscalls/syscall.tbl
@@ -471,3 +471,4 @@
 465	common	listxattrat			sys_listxattrat
 466	common	removexattrat			sys_removexattrat
 467	common	open_tree_attr			sys_open_tree_attr
+468	common	set_robust_list2		sys_set_robust_list2
diff --git a/arch/sparc/kernel/syscalls/syscall.tbl b/arch/sparc/kernel/syscalls/syscall.tbl
index 83e45eb6c095a36baaf749927628e6052fe900e6..8d1122c2235b8d5082a11392e68787efe55f58be 100644
--- a/arch/sparc/kernel/syscalls/syscall.tbl
+++ b/arch/sparc/kernel/syscalls/syscall.tbl
@@ -513,3 +513,4 @@
 465	common	listxattrat			sys_listxattrat
 466	common	removexattrat			sys_removexattrat
 467	common	open_tree_attr			sys_open_tree_attr
+468	common	set_robust_list2		sys_set_robust_list2
diff --git a/arch/x86/entry/syscalls/syscall_32.tbl b/arch/x86/entry/syscalls/syscall_32.tbl
index ac007ea00979dc28b0ef7c002a0615ce86dd3101..cbc0c469e66ecf7b8a61e82c38b07ecc63f6fe23 100644
--- a/arch/x86/entry/syscalls/syscall_32.tbl
+++ b/arch/x86/entry/syscalls/syscall_32.tbl
@@ -473,3 +473,4 @@
 465	i386	listxattrat		sys_listxattrat
 466	i386	removexattrat		sys_removexattrat
 467	i386	open_tree_attr		sys_open_tree_attr
+468	i386	set_robust_list2	sys_set_robust_list2
diff --git a/arch/x86/entry/syscalls/syscall_64.tbl b/arch/x86/entry/syscalls/syscall_64.tbl
index cfb5ca41e30de1a4e073750096f5b51a2ec137d2..b420217c72fc50ad90f291812972019606c5ff69 100644
--- a/arch/x86/entry/syscalls/syscall_64.tbl
+++ b/arch/x86/entry/syscalls/syscall_64.tbl
@@ -391,6 +391,7 @@
 465	common	listxattrat		sys_listxattrat
 466	common	removexattrat		sys_removexattrat
 467	common	open_tree_attr		sys_open_tree_attr
+468	common	set_robust_list2	sys_set_robust_list2
 
 #
 # Due to a historical design error, certain syscalls are numbered differently
diff --git a/arch/xtensa/kernel/syscalls/syscall.tbl b/arch/xtensa/kernel/syscalls/syscall.tbl
index f657a77314f8667fa019a01e10c84ea270024adc..6b852ee8a1621c7dd24f6cd37fd990f5ff8d8527 100644
--- a/arch/xtensa/kernel/syscalls/syscall.tbl
+++ b/arch/xtensa/kernel/syscalls/syscall.tbl
@@ -438,3 +438,4 @@
 465	common	listxattrat			sys_listxattrat
 466	common	removexattrat			sys_removexattrat
 467	common	open_tree_attr			sys_open_tree_attr
+468	common	set_robust_list2		sys_set_robust_list2
diff --git a/kernel/sys_ni.c b/kernel/sys_ni.c
index c00a86931f8c6cb30d35a9d56cbcc5994add90e1..71fbac6176c8886f4fa8dd437b0aedd5f14e9f74 100644
--- a/kernel/sys_ni.c
+++ b/kernel/sys_ni.c
@@ -195,6 +195,7 @@ COND_SYSCALL(move_pages);
 COND_SYSCALL(set_mempolicy_home_node);
 COND_SYSCALL(cachestat);
 COND_SYSCALL(mseal);
+COND_SYSCALL(set_robust_list2);
 
 COND_SYSCALL(perf_event_open);
 COND_SYSCALL(accept4);
diff --git a/scripts/syscall.tbl b/scripts/syscall.tbl
index 580b4e246aecd5f07d542943ba68fc4ed5961660..07d7e776d0329659e70a9a55ffff7ac18eb3ff87 100644
--- a/scripts/syscall.tbl
+++ b/scripts/syscall.tbl
@@ -408,3 +408,4 @@
 465	common	listxattrat			sys_listxattrat
 466	common	removexattrat			sys_removexattrat
 467	common	open_tree_attr			sys_open_tree_attr
+468	common	set_robust_list2		sys_set_robust_list2

-- 
2.49.0

[PATCH RESEND v4 6/7] futex: Remove the limit of elements for sys_set_robust_list2 lists

[André Almeida]

Remove the limit of ROBUST_LIST_LIMIT elements that a robust list can
have, for the ones created with the new interface. This is done by
overwritten the list as it's proceeded in a way that we avoid circular
lists.

For the old interface, we keep the limited behavior to avoid changing
the API.

Signed-off-by: André Almeida <andrealmeid@igalia.com>
---
 kernel/futex/core.c | 50 ++++++++++++++++++++++++++++++++++++--------------
 1 file changed, 36 insertions(+), 14 deletions(-)

diff --git a/kernel/futex/core.c b/kernel/futex/core.c
index 49b3bc592948a811f995017027f33ad8f285531f..61f0b48a2bcd8ab926754980ab3454b9ec13a344 100644
--- a/kernel/futex/core.c
+++ b/kernel/futex/core.c
@@ -1152,7 +1152,8 @@ static inline int fetch_robust_entry(struct robust_list __user **entry,
  * We silently return on any sign of list-walking problem.
  */
 static void exit_robust_list64(struct task_struct *curr,
-			       struct robust_list_head __user *head)
+			       struct robust_list_head __user *head,
+			       bool destroyable)
 {
 	struct robust_list __user *entry, *next_entry, *pending;
 	unsigned int limit = ROBUST_LIST_LIMIT, pi, pip;
@@ -1196,13 +1197,17 @@ static void exit_robust_list64(struct task_struct *curr,
 		}
 		if (rc)
 			return;
-		entry = next_entry;
-		pi = next_pi;
+
 		/*
 		 * Avoid excessively long or circular lists:
 		 */
-		if (!--limit)
+		if (!destroyable && !--limit)
 			break;
+		else
+			put_user(&head->list, &entry->next);
+
+		entry = next_entry;
+		pi = next_pi;
 
 		cond_resched();
 	}
@@ -1214,7 +1219,8 @@ static void exit_robust_list64(struct task_struct *curr,
 }
 #else
 static void exit_robust_list64(struct task_struct *curr,
-			      struct robust_list_head __user *head)
+			      struct robust_list_head __user *head,
+			      bool destroyable)
 {
 	pr_warn("32bit kernel should not allow ROBUST_LIST_64BIT");
 }
@@ -1252,7 +1258,8 @@ fetch_robust_entry32(u32 *uentry, struct robust_list __user **entry,
  * We silently return on any sign of list-walking problem.
  */
 static void exit_robust_list32(struct task_struct *curr,
-			       struct robust_list_head32 __user *head)
+			       struct robust_list_head32 __user *head,
+			       bool destroyable)
 {
 	struct robust_list __user *entry, *next_entry, *pending;
 	unsigned int limit = ROBUST_LIST_LIMIT, pi, pip;
@@ -1301,14 +1308,17 @@ static void exit_robust_list32(struct task_struct *curr,
 		}
 		if (rc)
 			return;
-		uentry = next_uentry;
-		entry = next_entry;
-		pi = next_pi;
 		/*
 		 * Avoid excessively long or circular lists:
 		 */
-		if (!--limit)
+		if (!destroyable && !--limit)
 			break;
+		else
+			put_user((struct robust_list __user *) &head->list, &entry->next);
+
+		uentry = next_uentry;
+		entry = next_entry;
+		pi = next_pi;
 
 		cond_resched();
 	}
@@ -1474,26 +1484,38 @@ static void exit_pi_state_list(struct task_struct *curr)
 static inline void exit_pi_state_list(struct task_struct *curr) { }
 #endif
 
+/*
+ * futex_cleanup - After the task exists, process the robust lists
+ *
+ * Walk through the linked list, parsing robust lists and freeing the
+ * allocated lists. Lists created with the set_robust_list2 don't have a limit
+ * for sizing and can be destroyed while we walk on it to avoid circular list.
+ */
 static void futex_cleanup(struct task_struct *tsk)
 {
 	struct robust_list2_entry *curr, *n;
 	struct list_head *list2 = &tsk->robust_list2;
+	bool destroyable = true;
+	int i = 0;
 
 	/*
-	 * Walk through the linked list, parsing robust lists and freeing the
-	 * allocated lists
 	 */
 	if (unlikely(!list_empty(list2))) {
 		list_for_each_entry_safe(curr, n, list2, list) {
+			destroyable = true;
+			if (tsk->robust_list_index == i)
+				destroyable = false;
+
 			if (curr->head != NULL) {
 				if (curr->list_type == ROBUST_LIST_64BIT)
-					exit_robust_list64(tsk, curr->head);
+					exit_robust_list64(tsk, curr->head, destroyable);
 				else if (curr->list_type == ROBUST_LIST_32BIT)
-					exit_robust_list32(tsk, curr->head);
+					exit_robust_list32(tsk, curr->head, destroyable);
 				curr->head = NULL;
 			}
 			list_del_init(&curr->list);
 			kfree(curr);
+			i++;
 		}
 	}
 

-- 
2.49.0

[PATCH RESEND v4 7/7] selftests: futex: Expand robust list test for the new interface

[André Almeida]

Expand the current robust list test for the new set_robust_list2
syscall. Create an option to make it possible to run the same tests
using the new syscall, and also add two new relevant test: test long
lists (bigger than ROBUST_LIST_LIMIT) and for unaligned addresses.

Signed-off-by: André Almeida <andrealmeid@igalia.com>
---
 .../selftests/futex/functional/robust_list.c       | 160 ++++++++++++++++++++-
 1 file changed, 156 insertions(+), 4 deletions(-)

diff --git a/tools/testing/selftests/futex/functional/robust_list.c b/tools/testing/selftests/futex/functional/robust_list.c
index 42690b2440fd29a9b12c46f67f9645ccc93d1147..004ad79ff6171c411fd47e699e3c38889544218e 100644
--- a/tools/testing/selftests/futex/functional/robust_list.c
+++ b/tools/testing/selftests/futex/functional/robust_list.c
@@ -35,16 +35,45 @@
 #include <stddef.h>
 #include <sys/mman.h>
 #include <sys/wait.h>
+#include <stdint.h>
 
 #define STACK_SIZE (1024 * 1024)
 
 #define FUTEX_TIMEOUT 3
 
+#define SYS_set_robust_list2 468
+
+enum robust_list2_type {
+        ROBUST_LIST_32BIT,
+        ROBUST_LIST_64BIT,
+};
+
 static pthread_barrier_t barrier, barrier2;
 
+bool robust2 = false;
+
 int set_robust_list(struct robust_list_head *head, size_t len)
 {
-	return syscall(SYS_set_robust_list, head, len);
+	int ret, flags;
+
+	if (!robust2) {
+		return syscall(SYS_set_robust_list, head, len);
+	}
+
+	if (sizeof(head) == 8)
+		flags = ROBUST_LIST_64BIT;
+	else
+		flags = ROBUST_LIST_32BIT;
+
+	/*
+	 * We act as we have just one list here. We try to use the first slot,
+	 * but if it hasn't been alocated yet we allocate it.
+	 */
+	ret = syscall(SYS_set_robust_list2, head, 0, flags);
+	if (ret == -1 && errno == ENOENT)
+		ret = syscall(SYS_set_robust_list2, head, -1, flags);
+
+	return ret;
 }
 
 int get_robust_list(int pid, struct robust_list_head **head, size_t *len_ptr)
@@ -246,6 +275,11 @@ static void test_set_robust_list_invalid_size(void)
 	size_t head_size = sizeof(struct robust_list_head);
 	int ret;
 
+	if (robust2) {
+		ksft_test_result_skip("This test is only for old robust interface\n");
+		return;
+	}
+
 	ret = set_robust_list(&head, head_size);
 	ASSERT_EQ(ret, 0);
 
@@ -321,6 +355,11 @@ static void test_get_robust_list_child(void)
 	struct robust_list_head head, *get_head;
 	size_t len_ptr;
 
+	if (robust2) {
+		ksft_test_result_skip("Not implemented in the new robust interface\n");
+		return;
+	}
+
 	ret = pthread_barrier_init(&barrier, NULL, 2);
 	ret = pthread_barrier_init(&barrier2, NULL, 2);
 	ASSERT_EQ(ret, 0);
@@ -332,7 +371,7 @@ static void test_get_robust_list_child(void)
 
 	ret = get_robust_list(tid, &get_head, &len_ptr);
 	ASSERT_EQ(ret, 0);
-	ASSERT_EQ(&head, get_head);
+	ASSERT_EQ(get_head, &head);
 
 	pthread_barrier_wait(&barrier2);
 
@@ -507,11 +546,119 @@ static void test_circular_list(void)
 	ksft_test_result_pass("%s\n", __func__);
 }
 
+#define ROBUST_LIST_LIMIT	2048
+#define CHILD_LIST_LIMIT (ROBUST_LIST_LIMIT + 10)
+
+static int child_robust_list_limit(void *arg)
+{
+	struct lock_struct *locks;
+	struct robust_list *list;
+	struct robust_list_head head;
+	int ret, i;
+
+	locks = (struct lock_struct *) arg;
+
+	ret = set_list(&head);
+	if (ret)
+		ksft_test_result_fail("set_list error\n");
+
+	/*
+	 * Create a very long list of locks
+	 */
+	head.list.next = &locks[0].list;
+
+	list = head.list.next;
+	for (i = 0; i < CHILD_LIST_LIMIT - 1; i++) {
+		list->next = &locks[i+1].list;
+		list = list->next;
+	}
+	list->next = &head.list;
+
+	/*
+	 * Grab the lock in the last one, and die without releasing it
+	 */
+	mutex_lock(&locks[CHILD_LIST_LIMIT], &head, false);
+	pthread_barrier_wait(&barrier);
+
+	sleep(1);
+
+	return 0;
+}
+
+/*
+ * The old robust list used to have a limit of 2048 items from the kernel side.
+ * After this limit the kernel stops walking the list and ignore the other
+ * futexes, causing deadlocks.
+ *
+ * For the new interface, test if we can wait for a list of more than 2048
+ * elements.
+ */
+static void test_robust_list_limit(void)
+{
+	struct lock_struct locks[CHILD_LIST_LIMIT + 1];
+	_Atomic(unsigned int) *futex = &locks[CHILD_LIST_LIMIT].futex;
+	struct robust_list_head head;
+	int ret;
+
+	if (!robust2) {
+		ksft_test_result_skip("This test is only for new robust interface\n");
+		return;
+	}
+
+	*futex = 0;
+
+	ret = set_list(&head);
+	ASSERT_EQ(ret, 0);
+
+	ret = pthread_barrier_init(&barrier, NULL, 2);
+	ASSERT_EQ(ret, 0);
+
+	create_child(child_robust_list_limit, locks);
+
+	/*
+	 * After the child thread creates the very long list of locks, wait on
+	 * the last one.
+	 */
+	pthread_barrier_wait(&barrier);
+	ret = mutex_lock(&locks[CHILD_LIST_LIMIT], &head, false);
+
+	if (ret != 0)
+		printf("futex wait returned %d\n", errno);
+	ASSERT_EQ(ret, 0);
+
+	ASSERT_TRUE(*futex | FUTEX_OWNER_DIED);
+
+	wait(NULL);
+	pthread_barrier_destroy(&barrier);
+
+	ksft_test_result_pass("%s\n", __func__);
+}
+
+/*
+ * The kernel should refuse an unaligned head pointer
+ */
+static void test_unaligned_address(void)
+{
+	struct robust_list_head head, *h;
+	int ret;
+
+	if (!robust2) {
+		ksft_test_result_skip("This test is only for new robust interface\n");
+		return;
+	}
+
+	h = (struct robust_list_head *) ((uintptr_t) &head + 1);
+	ret = set_list(h);
+	ASSERT_EQ(ret, -1);
+	ASSERT_EQ(errno, EINVAL);
+}
+
 void usage(char *prog)
 {
 	printf("Usage: %s\n", prog);
 	printf("  -c	Use color\n");
 	printf("  -h	Display this help message\n");
+	printf("  -n	Use robust2 syscall\n");
 	printf("  -v L	Verbosity level: %d=QUIET %d=CRITICAL %d=INFO\n",
 	       VQUIET, VCRITICAL, VINFO);
 }
@@ -520,7 +667,7 @@ int main(int argc, char *argv[])
 {
 	int c;
 
-	while ((c = getopt(argc, argv, "cht:v:")) != -1) {
+	while ((c = getopt(argc, argv, "chnt:v:")) != -1) {
 		switch (c) {
 		case 'c':
 			log_color(1);
@@ -531,6 +678,9 @@ int main(int argc, char *argv[])
 		case 'v':
 			log_verbosity(atoi(optarg));
 			break;
+		case 'n':
+			robust2 = true;
+			break;
 		default:
 			usage(basename(argv[0]));
 			exit(1);
@@ -538,7 +688,7 @@ int main(int argc, char *argv[])
 	}
 
 	ksft_print_header();
-	ksft_set_plan(7);
+	ksft_set_plan(8);
 
 	test_robustness();
 
@@ -548,6 +698,8 @@ int main(int argc, char *argv[])
 	test_set_list_op_pending();
 	test_robust_list_multiple_elements();
 	test_circular_list();
+	test_robust_list_limit();
+	test_unaligned_address();
 
 	ksft_print_cnts();
 	return 0;

-- 
2.49.0

Re: [PATCH RESEND v4 0/7] futex: Create set_robust_list2

[Sebastian Andrzej Siewior]

On 2025-06-17 15:34:17 [-0300], André Almeida wrote:
> This patch adds a new robust_list() syscall. The current syscall
> can't be expanded to cover the following use case, so a new one is
> needed. This new syscall allows users to set multiple robust lists per
> process and to have either 32bit or 64bit pointers in the list.

Thank you for the reminder. It was on my list, it slipped. Two
questions:
- there was a bot warning for v3 but this v4 is a RESEND. It the warning
  addressed in any way?

- You say 64bit x86-64 does not have the problem due the compat syscall.
  Arm64 has this problem. New arm64 do not provide arm32 facility. You
  introduce the syscall here. Why not introduce the compat syscall
  instead? I'm sorry if this has been answered somewhere below but this
  was one question I had while I initially skimmed over the patches.

Sebastian

Re: [PATCH RESEND v4 0/7] futex: Create set_robust_list2

[André Almeida]

Hi Sebastian,

Thanks for the feedback!

Em 18/06/2025 04:08, Sebastian Andrzej Siewior escreveu:
> On 2025-06-17 15:34:17 [-0300], André Almeida wrote:
>> This patch adds a new robust_list() syscall. The current syscall
>> can't be expanded to cover the following use case, so a new one is
>> needed. This new syscall allows users to set multiple robust lists per
>> process and to have either 32bit or 64bit pointers in the list.
> 
> Thank you for the reminder. It was on my list, it slipped. Two
> questions:
> - there was a bot warning for v3 but this v4 is a RESEND. It the warning
>    addressed in any way?
> 

Ops, I forgot to address them. I will do it for v5.

> - You say 64bit x86-64 does not have the problem due the compat syscall.
>    Arm64 has this problem. New arm64 do not provide arm32 facility. You
>    introduce the syscall here. Why not introduce the compat syscall
>    instead? I'm sorry if this has been answered somewhere below but this
>    was one question I had while I initially skimmed over the patches.
> 

The main target for this new syscall is Arm64, that can't handle 32 
pointers in the current syscall, so this new interface allows the robust 
list mechanism to know if it needs to do 64 or 32 bit pointer arithmetic 
operations to walk in the list.

Introducing a compat syscall won't fix this, giving that it only works 
in x86-64. We need an entry point for Arm64 that can handle 32 bit pointers.

I hope that it's clear now, let me know if you have more questions :)

> Sebastian

Re: [PATCH RESEND v4 0/7] futex: Create set_robust_list2

[Sebastian Andrzej Siewior]

On 2025-06-18 13:39:46 [-0300], André Almeida wrote:
> 
> Ops, I forgot to address them. I will do it for v5.
> 
> > - You say 64bit x86-64 does not have the problem due the compat syscall.
> >    Arm64 has this problem. New arm64 do not provide arm32 facility. You
> >    introduce the syscall here. Why not introduce the compat syscall
> >    instead? I'm sorry if this has been answered somewhere below but this
> >    was one question I had while I initially skimmed over the patches.
> > 
> 
> The main target for this new syscall is Arm64, that can't handle 32 pointers
> in the current syscall, so this new interface allows the robust list
> mechanism to know if it needs to do 64 or 32 bit pointer arithmetic
> operations to walk in the list.
> 
> Introducing a compat syscall won't fix this, giving that it only works in
> x86-64. We need an entry point for Arm64 that can handle 32 bit pointers.

I would need to dig into details to figure out why it won't work for
arm64 and works only for x86-64. 
There is the set_robust_list syscall as compat which sets
::compat_robust_list. And non-compat sets ::robust_list. The 32bit
application on 64bit kernel should set ::compat_robust_list which what
your syscall provides.
That is why I don't understand the need for it so far. Maybe I am
missing a detail.
We have other architectures with 64 bit kernel and a possible 32bit
userland such as mips, s390 or powerpc which would have the same issue
then. Or there is something special about arm64 in this case which makes
it unique.

Sebastian

Re: [PATCH RESEND v4 0/7] futex: Create set_robust_list2

[Arnd Bergmann]

On Wed, Jun 18, 2025, at 18:56, Sebastian Andrzej Siewior wrote:
> On 2025-06-18 13:39:46 [-0300], André Almeida wrote:
>> 
>> Ops, I forgot to address them. I will do it for v5.
>> 
>> > - You say 64bit x86-64 does not have the problem due the compat syscall.
>> >    Arm64 has this problem. New arm64 do not provide arm32 facility. You
>> >    introduce the syscall here. Why not introduce the compat syscall
>> >    instead? I'm sorry if this has been answered somewhere below but this
>> >    was one question I had while I initially skimmed over the patches.
>> > 
>> 
>> The main target for this new syscall is Arm64, that can't handle 32 pointers
>> in the current syscall, so this new interface allows the robust list
>> mechanism to know if it needs to do 64 or 32 bit pointer arithmetic
>> operations to walk in the list.
>> 
>> Introducing a compat syscall won't fix this, giving that it only works in
>> x86-64. We need an entry point for Arm64 that can handle 32 bit pointers.
>
> I would need to dig into details to figure out why it won't work for
> arm64 and works only for x86-64. 
> There is the set_robust_list syscall as compat which sets
> ::compat_robust_list. And non-compat sets ::robust_list. The 32bit
> application on 64bit kernel should set ::compat_robust_list which what
> your syscall provides.
> That is why I don't understand the need for it so far. Maybe I am
> missing a detail.
> We have other architectures with 64 bit kernel and a possible 32bit
> userland such as mips, s390 or powerpc which would have the same issue
> then. Or there is something special about arm64 in this case which makes
> it unique.

x86 is the special case here, since it allows applications to
call both the 32-bit (compat) and 64-bit syscalls directly on
a 64-bit kernel. I think MIPS may do that as well, but the other
architectures only allow a process to call syscalls for its native
ABI, so the only way to call a compat syscall is from a 32-bit
task. On Arm and RISC-V it's also common to have CPUs that cannot
run 32-bit tasks at all, so even running your x86-32 emulator as
an arm32 or rv32 task won't work.

      Arnd