From 15465a2c25cc2915e8c7c65178805b10e339dde3 Mon Sep 17 00:00:00 2001
From: Konstantin Belousov <kib@FreeBSD.org>
Date: Sun, 25 Apr 2021 03:01:32 +0300
Subject: [PATCH] Add sleepq_remove_nested()

The helper removes the thread from a sleep queue, assuming that it would
need to sleep. The sleepq_remove_nested() function is intended for quite
special case, where suspended thread from traced stopped process is
temporary unsuspended to do some work on behalf of the debugger in the
target context, and this work might require sleep.

Reviewed by:	markj
Tested by:	pho
Sponsored by:	The FreeBSD Foundation
MFC after:	1 week
Differential revision:	https://reviews.freebsd.org/D29955
---
 sys/kern/subr_sleepqueue.c | 20 ++++++++++++++++++++
 sys/sys/sleepqueue.h       |  1 +
 2 files changed, 21 insertions(+)

diff --git a/sys/kern/subr_sleepqueue.c b/sys/kern/subr_sleepqueue.c
index 20ca455480b5..0718f01fa48a 100644
--- a/sys/kern/subr_sleepqueue.c
+++ b/sys/kern/subr_sleepqueue.c
@@ -854,6 +854,26 @@ sleepq_remove_thread(struct sleepqueue *sq, struct thread *td)
 	    (void *)td, (long)td->td_proc->p_pid, td->td_name);
 }
 
+void
+sleepq_remove_nested(struct thread *td)
+{
+	struct sleepqueue_chain *sc;
+	struct sleepqueue *sq;
+	const void *wchan;
+
+	MPASS(TD_ON_SLEEPQ(td));
+
+	wchan = td->td_wchan;
+	sc = SC_LOOKUP(wchan);
+	mtx_lock_spin(&sc->sc_lock);
+	sq = sleepq_lookup(wchan);
+	MPASS(sq != NULL);
+	thread_lock(td);
+	sleepq_remove_thread(sq, td);
+	mtx_unlock_spin(&sc->sc_lock);
+	/* Returns with the thread lock owned. */
+}
+
 #ifdef INVARIANTS
 /*
  * UMA zone item deallocator.
diff --git a/sys/sys/sleepqueue.h b/sys/sys/sleepqueue.h
index ba2f85f2c8a1..18c7568777b6 100644
--- a/sys/sys/sleepqueue.h
+++ b/sys/sys/sleepqueue.h
@@ -100,6 +100,7 @@ void	sleepq_release(const void *wchan);
 void	sleepq_remove(struct thread *td, const void *wchan);
 int	sleepq_remove_matching(struct sleepqueue *sq, int queue,
 	    bool (*matches)(struct thread *), int pri);
+void	sleepq_remove_nested(struct thread *td);
 int	sleepq_signal(const void *wchan, int flags, int pri, int queue);
 void	sleepq_set_timeout_sbt(const void *wchan, sbintime_t sbt,
 	    sbintime_t pr, int flags);