From af928fded0705100e4f3926c99ed488f7ab6dcf1 Mon Sep 17 00:00:00 2001
From: Konstantin Belousov <kib@FreeBSD.org>
Date: Sat, 24 Apr 2021 14:47:53 +0300
Subject: [PATCH] Add thread_run_flash() helper

It unsuspends single suspended thread, passed as the argument.
It is up to the caller to arrange the target thread to suspend later,
since the state of the process is not changed from stopped.  In particular,
the unsuspended thread must not leave to userspace, since boundary code
is not prepared to this situation.

Reviewed by:	markj
Tested by:	pho
Sponsored by:	The FreeBSD Foundation
MFC after:	1 week
Differential revision:	https://reviews.freebsd.org/D29955
---
 sys/kern/kern_thread.c | 25 +++++++++++++++++++++++++
 sys/sys/proc.h         |  1 +
 2 files changed, 26 insertions(+)

diff --git a/sys/kern/kern_thread.c b/sys/kern/kern_thread.c
index ea569576e7c..d5549baa6ad 100644
--- a/sys/kern/kern_thread.c
+++ b/sys/kern/kern_thread.c
@@ -1514,6 +1514,31 @@ thread_unsuspend_one(struct thread *td, struct proc *p, bool boundary)
 	return (setrunnable(td, 0));
 }
 
+void
+thread_run_flash(struct thread *td)
+{
+	struct proc *p;
+
+	p = td->td_proc;
+	PROC_LOCK_ASSERT(p, MA_OWNED);
+
+	if (TD_ON_SLEEPQ(td))
+		sleepq_remove_nested(td);
+	else
+		thread_lock(td);
+
+	THREAD_LOCK_ASSERT(td, MA_OWNED);
+	KASSERT(TD_IS_SUSPENDED(td), ("Thread not suspended"));
+
+	TD_CLR_SUSPENDED(td);
+	PROC_SLOCK(p);
+	MPASS(p->p_suspcount > 0);
+	p->p_suspcount--;
+	PROC_SUNLOCK(p);
+	if (setrunnable(td, 0))
+		kick_proc0();
+}
+
 /*
  * Allow all threads blocked by single threading to continue running.
  */
diff --git a/sys/sys/proc.h b/sys/sys/proc.h
index b82de183aa4..a078b859ddc 100644
--- a/sys/sys/proc.h
+++ b/sys/sys/proc.h
@@ -1191,6 +1191,7 @@ void	thread_stopped(struct proc *p);
 void	childproc_stopped(struct proc *child, int reason);
 void	childproc_continued(struct proc *child);
 void	childproc_exited(struct proc *child);
+void	thread_run_flash(struct thread *td);
 int	thread_suspend_check(int how);
 bool	thread_suspend_check_needed(void);
 void	thread_suspend_switch(struct thread *, struct proc *p);