From d87af38ca063b9782ed8e05a68691890f58d489c Mon Sep 17 00:00:00 2001
From: Matthew Dillon <dillon@apollo.backplane.com>
Date: Fri, 2 Aug 2013 10:46:40 -0700
Subject: [PATCH] kernel - Fix panic when usched is used to force a cpu w/the
 dfly scheduler

* Fix a panic for 'usched dfly:0x1 sh', or other similar cpu forcing
  mechanic.

* The scheduler was not being notified of the forced migration which
  caused it to assert on a sanity check later on.  Add the needed
  infrastructure.

Reported-by: vsrinivas
---
 sys/kern/usched_bsd4.c  | 10 +++++++++-
 sys/kern/usched_dfly.c  | 28 +++++++++++++++++++++++++++-
 sys/kern/usched_dummy.c | 10 +++++++++-
 sys/sys/usched.h        |  1 +
 4 files changed, 46 insertions(+), 3 deletions(-)

diff --git a/sys/kern/usched_bsd4.c b/sys/kern/usched_bsd4.c
index 1ea8afcf79..625050bce2 100644
--- a/sys/kern/usched_bsd4.c
+++ b/sys/kern/usched_bsd4.c
@@ -108,6 +108,7 @@ static void bsd4_kick_helper(struct lwp *lp);
 static struct lwp *bsd4_chooseproc_locked(struct lwp *chklp);
 static void bsd4_remrunqueue_locked(struct lwp *lp);
 static void bsd4_setrunqueue_locked(struct lwp *lp);
+static void bsd4_changedcpu(struct lwp *lp);
 
 struct usched usched_bsd4 = {
 	{ NULL },
@@ -124,7 +125,8 @@ struct usched usched_bsd4 = {
 	bsd4_exiting,
 	bsd4_uload_update,
 	NULL,			/* setcpumask not supported */
-	bsd4_yield
+	bsd4_yield,
+	bsd4_changedcpu
 };
 
 struct usched_bsd4_pcpu {
@@ -1209,6 +1211,12 @@ bsd4_yield(struct lwp *lp)
         need_user_resched();
 }
 
+static
+void
+bsd4_changedcpu(struct lwp *lp __unused)
+{
+}
+
 /*
  * Called from fork1() when a new child process is being created.
  *
diff --git a/sys/kern/usched_dfly.c b/sys/kern/usched_dfly.c
index e8cba632fb..32a7511445 100644
--- a/sys/kern/usched_dfly.c
+++ b/sys/kern/usched_dfly.c
@@ -144,6 +144,7 @@ static struct lwp *dfly_chooseproc_locked(dfly_pcpu_t rdd, dfly_pcpu_t dd,
 					  struct lwp *chklp, int worst);
 static void dfly_remrunqueue_locked(dfly_pcpu_t dd, struct lwp *lp);
 static void dfly_setrunqueue_locked(dfly_pcpu_t dd, struct lwp *lp);
+static void dfly_changedcpu(struct lwp *lp);
 
 struct usched usched_dfly = {
 	{ NULL },
@@ -160,7 +161,8 @@ struct usched usched_dfly = {
 	dfly_exiting,
 	dfly_uload_update,
 	NULL,			/* setcpumask not supported */
-	dfly_yield
+	dfly_yield,
+	dfly_changedcpu
 };
 
 /*
@@ -1135,6 +1137,30 @@ dfly_yield(struct lwp *lp)
         need_user_resched();
 }
 
+/*
+ * Thread was forcefully migrated to another cpu.  Normally forced migrations
+ * are used for iterations and the kernel returns to the original cpu before
+ * returning and this is not needed.  However, if the kernel migrates a
+ * thread to another cpu and wants to leave it there, it has to call this
+ * scheduler helper.
+ *
+ * Note that the lwkt_migratecpu() function also released the thread, so
+ * we don't have to worry about that.
+ */
+static
+void
+dfly_changedcpu(struct lwp *lp)
+{
+	dfly_pcpu_t dd = &dfly_pcpu[lp->lwp_qcpu];
+	dfly_pcpu_t rdd = &dfly_pcpu[mycpu->gd_cpuid];
+
+	if (dd != rdd) {
+		spin_lock(&dd->spin);
+		dfly_changeqcpu_locked(lp, dd, rdd);
+		spin_unlock(&dd->spin);
+	}
+}
+
 /*
  * Called from fork1() when a new child process is being created.
  *
diff --git a/sys/kern/usched_dummy.c b/sys/kern/usched_dummy.c
index 85413748cd..919e27a0a9 100644
--- a/sys/kern/usched_dummy.c
+++ b/sys/kern/usched_dummy.c
@@ -72,6 +72,7 @@ static void dummy_forking(struct lwp *plp, struct lwp *lp);
 static void dummy_exiting(struct lwp *plp, struct proc *child);
 static void dummy_uload_update(struct lwp *lp);
 static void dummy_yield(struct lwp *lp);
+static void dummy_changedcpu(struct lwp *lp);
 
 struct usched usched_dummy = {
 	{ NULL },
@@ -88,7 +89,8 @@ struct usched usched_dummy = {
 	dummy_exiting,
 	dummy_uload_update,
 	NULL,			/* setcpumask not supported */
-	dummy_yield
+	dummy_yield,
+	dummy_changedcpu
 };
 
 struct usched_dummy_pcpu {
@@ -366,6 +368,12 @@ dummy_yield(struct lwp *lp)
 	need_user_resched();
 }
 
+static
+void
+dummy_changedcpu(struct lwp *lp __unused)
+{
+}
+
 /*
  * DUMMY_RESETPRIORITY
  *
diff --git a/sys/sys/usched.h b/sys/sys/usched.h
index 664b85f8c6..6285e62713 100644
--- a/sys/sys/usched.h
+++ b/sys/sys/usched.h
@@ -44,6 +44,7 @@ struct usched {
     void (*uload_update)(struct lwp *);
     void (*setcpumask)(struct usched *, cpumask_t);
     void (*yield)(struct lwp *);
+    void (*changedcpu)(struct lwp *);
 };
 
 union usched_data {
-- 
2.41.0