[PATCH v3 13/13] kernel: Enable waitpid() for futex2
From: André Almeida <hidden>
Date: 2021-04-27 23:16:30
Also in:
linux-kselftest, lkml
Subsystem:
abi/api, exec & binfmt api, elf, memory management - core, scheduler, the rest · Maintainers:
Kees Cook, Andrew Morton, David Hildenbrand, Ingo Molnar, Peter Zijlstra, Juri Lelli, Vincent Guittot, Linus Torvalds
To make pthreads works as expected if they are using futex2, wake clear_child_tid with futex2 as well. This is make applications that uses waitpid() (and clone(CLONE_CHILD_SETTID)) wake while waiting for the child to terminate. Given that apps should not mix futex() and futex2(), any correct app will trigger a harmless noop wakeup on the interface that it isn't using. Signed-off-by: André Almeida <redacted> --- This commit is here for the intend to show what we need to do in order to get a full NPTL working on top of futex2. It should be merged after we talk to glibc folks on the details around the futex_wait() side. For instance, we could use this as an opportunity to use private futexes or 8bit sized futexes, but both sides need to use the exactly same flags. --- include/linux/syscalls.h | 2 ++ kernel/fork.c | 2 ++ kernel/futex2.c | 30 ++++++++++++++++++------------ 3 files changed, 22 insertions(+), 12 deletions(-)
diff --git a/include/linux/syscalls.h b/include/linux/syscalls.h
index d5a485cf52c4..59655c9317e6 100644
--- a/include/linux/syscalls.h
+++ b/include/linux/syscalls.h@@ -1315,6 +1315,8 @@ int ksys_ipc(unsigned int call, int first, unsigned long second, unsigned long third, void __user * ptr, long fifth); int compat_ksys_ipc(u32 call, int first, int second, u32 third, u32 ptr, u32 fifth); +long ksys_futex_wake(void __user *uaddr, unsigned long nr_wake, + unsigned int flags); /* * The following kernel syscall equivalents are just wrappers to fs-internal
diff --git a/kernel/fork.c b/kernel/fork.c
index 426cd0c51f9e..9f99273b161b 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c@@ -1316,6 +1316,8 @@ static void mm_release(struct task_struct *tsk, struct mm_struct *mm) put_user(0, tsk->clear_child_tid); do_futex(tsk->clear_child_tid, FUTEX_WAKE, 1, NULL, NULL, 0, 0); + ksys_futex_wake(tsk->clear_child_tid, 1, + FUTEX_32 | FUTEX_SHARED_FLAG); } tsk->clear_child_tid = NULL; }
diff --git a/kernel/futex2.c b/kernel/futex2.c
index 321472593e6f..901edf41d558 100644
--- a/kernel/futex2.c
+++ b/kernel/futex2.c@@ -937,18 +937,8 @@ static inline bool futex_match(struct futex_key key1, struct futex_key key2) key1.offset == key2.offset); } -/** - * sys_futex_wake - Wake a number of futexes waiting on an address - * @uaddr: Address of futex to be woken up - * @nr_wake: Number of futexes waiting in uaddr to be woken up - * @flags: Flags for size and shared - * - * Wake `nr_wake` threads waiting at uaddr. - * - * Returns the number of woken threads on success, error code otherwise. - */ -SYSCALL_DEFINE3(futex_wake, void __user *, uaddr, unsigned int, nr_wake, - unsigned int, flags) +long ksys_futex_wake(void __user *uaddr, unsigned long nr_wake, + unsigned int flags) { bool shared = (flags & FUTEX_SHARED_FLAG) ? true : false; unsigned int size = flags & FUTEX_SIZE_MASK;
@@ -985,6 +975,22 @@ SYSCALL_DEFINE3(futex_wake, void __user *, uaddr, unsigned int, nr_wake, return ret; } +/** + * sys_futex_wake - Wake a number of futexes waiting on an address + * @uaddr: Address of futex to be woken up + * @nr_wake: Number of futexes waiting in uaddr to be woken up + * @flags: Flags for size and shared + * + * Wake `nr_wake` threads waiting at uaddr. + * + * Returns the number of woken threads on success, error code otherwise. + */ +SYSCALL_DEFINE3(futex_wake, void __user *, uaddr, unsigned int, nr_wake, + unsigned int, flags) +{ + return ksys_futex_wake(uaddr, nr_wake, flags); +} + static void futex_double_unlock(struct futex_bucket *b1, struct futex_bucket *b2) { spin_unlock(&b1->lock);
--
2.31.1