Re: [PATCH v2 05/14] futex: Add sys_futex_wake()

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Hi Peter,

Em 07/08/2023 09:18, Peter Zijlstra escreveu:
To complement sys_futex_waitv() add sys_futex_wake(). This syscall
implements what was previously known as FUTEX_WAKE_BITSET except it
uses 'unsigned long' for the bitmask and takes FUTEX2 flags.

The 'unsigned long' allows FUTEX2_SIZE_U64 on 64bit platforms.

Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
Acked-by: Geert Uytterhoeven <geert@xxxxxxxxxxxxxx>
---

[...]

+/*
+ * sys_futex_wake - Wake a number of futexes
+ * @uaddr:	Address of the futex(es) to wake
+ * @mask:	bitmask
+ * @nr:		Number of the futexes to wake
+ * @flags:	FUTEX2 flags
+ *
+ * Identical to the traditional FUTEX_WAKE_BITSET op, except it is part of the
+ * futex2 family of calls.
+ */
+
+SYSCALL_DEFINE4(futex_wake,
+		void __user *, uaddr,
+		unsigned long, mask,
+		int, nr,
+		unsigned int, flags)
+{

Do you think we could have a

	if (!nr)
		return 0;

here? Otherwise, calling futex_wake(&f, 0, flags) will wake 1 futex (if available), which is a strange undocumented behavior in my opinion.

+	if (flags & ~FUTEX2_VALID_MASK)
+		return -EINVAL;
+
+	flags = futex2_to_flags(flags);
+	if (!futex_flags_valid(flags))
+		return -EINVAL;
+
+	if (!futex_validate_input(flags, mask))
+		return -EINVAL;
+
+	return futex_wake(uaddr, flags, nr, mask);
+}
+
  #ifdef CONFIG_COMPAT
  COMPAT_SYSCALL_DEFINE2(set_robust_list,
  		struct compat_robust_list_head __user *, head,
--- a/kernel/sys_ni.c
+++ b/kernel/sys_ni.c
@@ -87,6 +87,7 @@ COND_SYSCALL_COMPAT(set_robust_list);
  COND_SYSCALL(get_robust_list);
  COND_SYSCALL_COMPAT(get_robust_list);
  COND_SYSCALL(futex_waitv);
+COND_SYSCALL(futex_wake);
  COND_SYSCALL(kexec_load);
  COND_SYSCALL_COMPAT(kexec_load);
  COND_SYSCALL(init_module);





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