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 andrealmeid@collabora.com ---
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 b9c2874410d0..85b5a501fb96 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 int 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 b4386ff6a641..f3f98e197fb6 100644 --- a/kernel/fork.c +++ b/kernel/fork.c @@ -1328,6 +1328,8 @@ 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 4f6d099badec..2ca2f40fcdd2 100644 --- a/kernel/futex2.c +++ b/kernel/futex2.c @@ -420,18 +420,8 @@ COMPAT_SYSCALL_DEFINE4(futex_wait, void __user *, uaddr, compat_u64, val, } #endif
-/** - * 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 int nr_wake, + unsigned int flags) { unsigned int size = flags & FUTEX_SIZE_MASK, futex_flags = 0;
@@ -447,6 +437,22 @@ SYSCALL_DEFINE3(futex_wake, void __user *, uaddr, unsigned int, nr_wake, return futex_wake(uaddr, futex_flags, nr_wake, FUTEX_BITSET_MATCH_ANY); }
+/** + * 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); +} + #ifdef CONFIG_COMPAT static int compat_futex_parse_requeue(struct compat_futex_requeue __user *rq, void __user **uaddr, unsigned int *flags)