linux-kernel - [PATCH 5/7] init: Deal with the init process being a user mode process

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Date:   Fri,  6 May 2022 09:15:10 -0500
From:   "Eric W. Biederman" <ebiederm@...ssion.com>
To:     linux-arch@...r.kernel.org
Cc:     Tejun Heo <tj@...nel.org>, Peter Zijlstra <peterz@...radead.org>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Al Viro <viro@...IV.linux.org.uk>,
        Jens Axboe <axboe@...nel.dk>,
        Thomas Gleixner <tglx@...utronix.de>,
        Linus Torvalds <torvalds@...uxfoundation.org>,
        linux-kernel@...r.kernel.org,
        "Eric W. Biederman" <ebiederm@...ssion.com>
Subject: [PATCH 5/7] init: Deal with the init process being a user mode process

It is silly for user_mode_thread to leave PF_KTHREAD set
on the resulting task.  Update the init process so that
it does not care if PF_KTHREAD is set or not.

Ensure do_populate_rootfs flushes all delayed fput work by calling
task_work_run.  In the rare instance that async_schedule_domain calls
do_populate_rootfs synchronously it is possible do_populate_rootfs
will be called directly from the init process.  At which point fput
will call "task_work_add(current, ..., TWA_RESUME)".  The files on the
initramfs need to be completely put before we attempt to exec them
(which is before the code enters userspace).  So call task_work_run
just in case there are any pending fput operations.

Signed-off-by: "Eric W. Biederman" <ebiederm@...ssion.com>
---
 init/initramfs.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/init/initramfs.c b/init/initramfs.c
index 2f3d96dc3db6..41e7857d510d 100644
--- a/init/initramfs.c
+++ b/init/initramfs.c
@@ -15,6 +15,7 @@
 #include <linux/mm.h>
 #include <linux/namei.h>
 #include <linux/init_syscalls.h>
+#include <linux/task_work.h>
 #include <linux/umh.h>

 static ssize_t __init xwrite(struct file *file, const char *p, size_t count,
@@ -703,6 +704,7 @@ static void __init do_populate_rootfs(void *unused, async_cookie_t cookie)
 	initrd_end = 0;

 	flush_delayed_fput();
+	task_work_run();
 }

 static ASYNC_DOMAIN_EXCLUSIVE(initramfs_domain);
-- 
2.35.3