kernel: Enable waitpid() for futex2

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: AndrÃ© Almeida <andrealmeid@collabora.com>
xanmod · Oct 2, 2021 · 442d05a · 442d05a
1 parent e5a1578
commit 442d05a
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Showing 3 changed files with 22 additions and 12 deletions.
diff --git a/include/linux/syscalls.h b/include/linux/syscalls.h
@@ -1326,6 +1326,8 @@ 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
@@ -1337,6 +1337,8 @@ 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
@@ -940,18 +940,8 @@ 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;
@@ -988,6 +978,22 @@ 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);