commit b13c84c1aa1d6983c4dede1d2ab6400ab879b179
Author: Ryota Ozaki <ozaki-r@iij.ad.jp>
Date:   Thu Nov 9 17:47:50 2017 +0900

    Add debugging features to pserialize(9)

diff --git a/sys/kern/kern_lock.c b/sys/kern/kern_lock.c
index 5f4d0a4183a..fd5e88a66ba 100644
--- a/sys/kern/kern_lock.c
+++ b/sys/kern/kern_lock.c
@@ -43,6 +43,7 @@ __KERNEL_RCSID(0, "$NetBSD: kern_lock.c,v 1.159 2017/09/16 23:55:33 christos Exp
 #include <sys/syslog.h>
 #include <sys/atomic.h>
 #include <sys/lwp.h>
+#include <sys/pserialize.h>
 
 #include <machine/lock.h>
 
@@ -88,6 +89,11 @@ assert_sleepable(void)
 	if (cpu_softintr_p()) {
 		reason = "softint";
 	}
+#ifdef LOCKDEBUG
+	if (pserialize_in_read_section()) {
+		reason = "pserialize";
+	}
+#endif
 
 	if (reason) {
 		panic("%s: %s caller=%p", __func__, reason,
diff --git a/sys/kern/subr_pserialize.c b/sys/kern/subr_pserialize.c
index 650f81f3092..53d14df05ac 100644
--- a/sys/kern/subr_pserialize.c
+++ b/sys/kern/subr_pserialize.c
@@ -73,6 +73,12 @@ static TAILQ_HEAD(, pserialize)	psz_queue0	__cacheline_aligned;
 static TAILQ_HEAD(, pserialize)	psz_queue1	__cacheline_aligned;
 static TAILQ_HEAD(, pserialize)	psz_queue2	__cacheline_aligned;
 
+#ifdef LOCKDEBUG
+#include <sys/percpu.h>
+
+static percpu_t		*psz_debug_nreads	__cacheline_aligned;
+#endif
+
 /*
  * pserialize_init:
  *
@@ -89,6 +95,9 @@ pserialize_init(void)
 	mutex_init(&psz_lock, MUTEX_DEFAULT, IPL_SCHED);
 	evcnt_attach_dynamic(&psz_ev_excl, EVCNT_TYPE_MISC, NULL,
 	    "pserialize", "exclusive access");
+#ifdef LOCKDEBUG
+	psz_debug_nreads = percpu_alloc(sizeof(int));
+#endif
 }
 
 /*
@@ -185,15 +194,35 @@ pserialize_perform(pserialize_t psz)
 int
 pserialize_read_enter(void)
 {
+	int s;
 
 	KASSERT(!cpu_intr_p());
-	return splsoftserial();
+	s = splsoftserial();
+#ifdef LOCKDEBUG
+	{
+		int *nreads;
+		nreads = percpu_getref(psz_debug_nreads);
+		(*nreads)++;
+		percpu_putref(psz_debug_nreads);
+	}
+#endif
+	return s;
 }
 
 void
 pserialize_read_exit(int s)
 {
 
+#ifdef LOCKDEBUG
+	{
+		int *nreads;
+		nreads = percpu_getref(psz_debug_nreads);
+		(*nreads)--;
+		if (*nreads < 0)
+			panic("nreads went negative: %d", *nreads);
+		percpu_putref(psz_debug_nreads);
+	}
+#endif
 	splx(s);
 }
 
@@ -209,6 +238,21 @@ pserialize_switchpoint(void)
 	pserialize_t psz, next;
 	cpuid_t cid;
 
+#ifdef LOCKDEBUG
+	/*
+	 * We must to ensure not to come here from inside a read section.
+	 */
+	{
+		int *nreads;
+		nreads = percpu_getref(psz_debug_nreads);
+		if (*nreads != 0) {
+			panic("trying to context-switch in a pserialize "
+			      "read section!");
+		}
+		percpu_putref(psz_debug_nreads);
+	}
+#endif
+
 	/*
 	 * If no updates pending, bail out.  No need to lock in order to
 	 * test psz_work_todo; the only ill effect of missing an update
@@ -261,3 +305,22 @@ pserialize_switchpoint(void)
 	}
 	mutex_spin_exit(&psz_lock);
 }
+
+#ifdef LOCKDEBUG
+bool
+pserialize_in_read_section(void)
+{
+	int *nreads;
+	bool in;
+
+	/* Not initialized yet */
+	if (__predict_false(psz_debug_nreads == NULL))
+		return false;
+
+	nreads = percpu_getref(psz_debug_nreads);
+	in = *nreads != 0;
+	percpu_putref(psz_debug_nreads);
+
+	return in;
+}
+#endif
diff --git a/sys/rump/librump/rumpkern/emul.c b/sys/rump/librump/rumpkern/emul.c
index a8ecd3886cd..b1c941ab303 100644
--- a/sys/rump/librump/rumpkern/emul.c
+++ b/sys/rump/librump/rumpkern/emul.c
@@ -165,11 +165,25 @@ calc_cache_size(vsize_t vasz, int pct, int va_pct)
 	return t;
 }
 
+#define	RETURN_ADDRESS	(uintptr_t)__builtin_return_address(0)
+
 void
 assert_sleepable(void)
 {
+	const char *reason = NULL;
 
 	/* always sleepable, although we should improve this */
+
+#ifdef LOCKDEBUG
+	if (pserialize_in_read_section()) {
+		reason = "pserialize";
+	}
+#endif
+
+	if (reason) {
+		panic("%s: %s caller=%p", __func__, reason,
+		    (void *)RETURN_ADDRESS);
+	}
 }
 
 void
diff --git a/sys/rump/librump/rumpkern/rump.c b/sys/rump/librump/rumpkern/rump.c
index fe85ae888f7..7719f7abb1e 100644
--- a/sys/rump/librump/rumpkern/rump.c
+++ b/sys/rump/librump/rumpkern/rump.c
@@ -301,6 +301,7 @@ rump_init(void)
 	callout_startup();
 
 	kprintf_init();
+	percpu_init();
 	pserialize_init();
 
 	kauth_init();
@@ -351,7 +352,6 @@ rump_init(void)
 	rump_schedule();
 	bootlwp = curlwp;
 
-	percpu_init();
 	inittimecounter();
 	ntp_init();
 
diff --git a/sys/sys/pserialize.h b/sys/sys/pserialize.h
index a1b36515e52..60d47d80672 100644
--- a/sys/sys/pserialize.h
+++ b/sys/sys/pserialize.h
@@ -44,6 +44,9 @@ void		pserialize_perform(pserialize_t);
 int		pserialize_read_enter(void);
 void		pserialize_read_exit(int);
 
+#ifdef LOCKDEBUG
+bool		pserialize_in_read_section(void);
+#endif
 #endif	/* _KERNEL */
 
 #endif	/* _SYS_PSERIALIZE_H_ */