[merged mm-nonmm-stable] fork-kill-the-pointless-lower_32_bits-in-create_io_thread-kernel_thread-and-user_mode_thread.patch removed from -mm tree

[merged mm-nonmm-stable] fork-kill-the-pointless-lower_32_bits-in-create_io_thread-kernel_thread-and-user_mode_thread.patch removed from -mm tree

[Andrew Morton]

The quilt patch titled
     Subject: fork: kill the pointless lower_32_bits() in create_io_thread(), kernel_thread(), and user_mode_thread()
has been removed from the -mm tree.  Its filename was
     fork-kill-the-pointless-lower_32_bits-in-create_io_thread-kernel_thread-and-user_mode_thread.patch

This patch was dropped because it was merged into the mm-nonmm-stable branch
of git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

------------------------------------------------------
From: Oleg Nesterov <oleg@redhat.com>
Subject: fork: kill the pointless lower_32_bits() in create_io_thread(), kernel_thread(), and user_mode_thread()
Date: Wed, 20 Aug 2025 18:39:46 +0200

Unlike sys_clone(), these helpers have only in kernel users which should
pass the correct "flags" argument.  lower_32_bits(flags) just adds the
unnecessary confusion and doesn't allow to use the CLONE_ flags which
don't fit into 32 bits.

create_io_thread() looks especially confusing because:

	- "flags" is a compile-time constant, so lower_32_bits() simply
	  has no effect

	- .exit_signal = (lower_32_bits(flags) & CSIGNAL) is harmless but
	  doesn't look right, copy_process(CLONE_THREAD) will ignore this
	  argument anyway.

None of these helpers actually need CLONE_UNTRACED or "& ~CSIGNAL", but
their presence does not add any confusion and improves code clarity.

Link: https://lkml.kernel.org/r/20250820163946.GA18549@redhat.com
Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Reviewed-by: Jens Axboe <axboe@kernel.dk>
Cc: Christian Brauner <brauner@kernel.org>
Cc: Kees Cook <kees@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 kernel/fork.c |   16 ++++++----------
 1 file changed, 6 insertions(+), 10 deletions(-)

--- a/kernel/fork.c~fork-kill-the-pointless-lower_32_bits-in-create_io_thread-kernel_thread-and-user_mode_thread
+++ a/kernel/fork.c
@@ -2537,11 +2537,9 @@ struct task_struct * __init fork_idle(in
 struct task_struct *create_io_thread(int (*fn)(void *), void *arg, int node)
 {
 	unsigned long flags = CLONE_FS|CLONE_FILES|CLONE_SIGHAND|CLONE_THREAD|
-				CLONE_IO;
+			      CLONE_IO|CLONE_VM|CLONE_UNTRACED;
 	struct kernel_clone_args args = {
-		.flags		= ((lower_32_bits(flags) | CLONE_VM |
-				    CLONE_UNTRACED) & ~CSIGNAL),
-		.exit_signal	= (lower_32_bits(flags) & CSIGNAL),
+		.flags		= flags,
 		.fn		= fn,
 		.fn_arg		= arg,
 		.io_thread	= 1,
@@ -2653,9 +2651,8 @@ pid_t kernel_thread(int (*fn)(void *), v
 		    unsigned long flags)
 {
 	struct kernel_clone_args args = {
-		.flags		= ((lower_32_bits(flags) | CLONE_VM |
-				    CLONE_UNTRACED) & ~CSIGNAL),
-		.exit_signal	= (lower_32_bits(flags) & CSIGNAL),
+		.flags		= ((flags | CLONE_VM | CLONE_UNTRACED) & ~CSIGNAL),
+		.exit_signal	= (flags & CSIGNAL),
 		.fn		= fn,
 		.fn_arg		= arg,
 		.name		= name,
@@ -2671,9 +2668,8 @@ pid_t kernel_thread(int (*fn)(void *), v
 pid_t user_mode_thread(int (*fn)(void *), void *arg, unsigned long flags)
 {
 	struct kernel_clone_args args = {
-		.flags		= ((lower_32_bits(flags) | CLONE_VM |
-				    CLONE_UNTRACED) & ~CSIGNAL),
-		.exit_signal	= (lower_32_bits(flags) & CSIGNAL),
+		.flags		= ((flags | CLONE_VM | CLONE_UNTRACED) & ~CSIGNAL),
+		.exit_signal	= (flags & CSIGNAL),
 		.fn		= fn,
 		.fn_arg		= arg,
 	};
_

Patches currently in -mm which might be from oleg@redhat.com are