Index: kern/subr_lockdebug.c
===================================================================
RCS file: /cvsroot/src/sys/kern/subr_lockdebug.c,v
retrieving revision 1.57
diff -u -u -r1.57 subr_lockdebug.c
--- kern/subr_lockdebug.c	1 Jun 2017 02:45:13 -0000	1.57
+++ kern/subr_lockdebug.c	26 Feb 2018 21:07:11 -0000
@@ -52,6 +52,8 @@
 #include <sys/lock.h>
 #include <sys/rbtree.h>
 
+#include <uvm/uvm.h>
+
 #include <machine/lock.h>
 
 unsigned int		ld_panic;
@@ -368,8 +370,11 @@
 	/*
 	 * Can't call kmem_alloc() if in interrupt context.  XXX We could
 	 * deadlock, because we don't know which locks the caller holds.
+	 * We also don't want to allocate more memory when called from
+	 * the pagedaemon, because we don't want to sleep.
 	 */
-	if (cpu_intr_p() || (curlwp->l_pflag & LP_INTR) != 0) {
+	if (cpu_intr_p() || (curlwp->l_pflag & LP_INTR) != 0
+	   || curlwp == uvm.pagedaemon_lwp) {
 		return s;
 	}
 
Index: uvm/uvm_pdaemon.c
===================================================================
RCS file: /cvsroot/src/sys/uvm/uvm_pdaemon.c,v
retrieving revision 1.108.22.1
diff -u -u -r1.108.22.1 uvm_pdaemon.c
--- uvm/uvm_pdaemon.c	2 Nov 2017 21:29:53 -0000	1.108.22.1
+++ uvm/uvm_pdaemon.c	26 Feb 2018 21:07:12 -0000
@@ -79,6 +79,7 @@
 #include <sys/buf.h>
 #include <sys/module.h>
 #include <sys/atomic.h>
+#include <sys/kthread.h>
 
 #include <uvm/uvm.h>
 #include <uvm/uvm_pdpolicy.h>
@@ -105,9 +106,16 @@
 static void	uvmpd_scan(void);
 static void	uvmpd_scan_queue(void);
 static void	uvmpd_tune(void);
+static void	uvmpd_pool_drain_thread(void *);
+static void	uvmpd_pool_drain_wakeup(void);
 
 static unsigned int uvm_pagedaemon_waiters;
 
+/* State for the pool drainer thread */
+static kmutex_t uvmpd_pool_drain_lock;
+static kcondvar_t uvmpd_pool_drain_cv;
+static bool uvmpd_pool_drain_run = false;
+
 /*
  * XXX hack to avoid hangs when large processes fork.
  */
@@ -229,14 +237,21 @@
 void
 uvm_pageout(void *arg)
 {
-	int bufcnt, npages = 0;
+	int npages = 0;
 	int extrapages = 0;
-	struct pool *pp;
 	
 	UVMHIST_FUNC("uvm_pageout"); UVMHIST_CALLED(pdhist);
 
 	UVMHIST_LOG(pdhist,"<starting uvm pagedaemon>", 0, 0, 0, 0);
 
+	mutex_init(&uvmpd_pool_drain_lock, MUTEX_DEFAULT, IPL_VM);
+	cv_init(&uvmpd_pool_drain_cv, "pooldrain");
+
+	/* Create the pool drainer kernel thread. */
+	if (kthread_create(PRI_VM, KTHREAD_MPSAFE, NULL,
+	    uvmpd_pool_drain_thread, NULL, NULL, "pooldrain"))
+		panic("fork pooldrain");
+
 	/*
 	 * ensure correct priority and set paging parameters...
 	 */
@@ -288,13 +303,9 @@
 		 * system only when entire pool page is empty.
 		 */
 		mutex_spin_enter(&uvm_fpageqlock);
-		bufcnt = uvmexp.freetarg - uvmexp.free;
-		if (bufcnt < 0)
-			bufcnt = 0;
 
 		UVMHIST_LOG(pdhist,"  free/ftarg=%jd/%jd",
 		    uvmexp.free, uvmexp.freetarg, 0,0);
-
 		needsfree = uvmexp.free + uvmexp.paging < uvmexp.freetarg;
 		needsscan = needsfree || uvmpdpol_needsscan_p();
 
@@ -331,16 +342,10 @@
 			continue;
 
 		/*
-		 * kill unused metadata buffers.
+		 * kick the pool drainer thread.
 		 */
-		mutex_enter(&bufcache_lock);
-		buf_drain(bufcnt << PAGE_SHIFT);
-		mutex_exit(&bufcache_lock);
 
-		/*
-		 * drain the pools.
-		 */
-		pool_drain(&pp);
+		uvmpd_pool_drain_wakeup();
 	}
 	/*NOTREACHED*/
 }
@@ -1022,3 +1027,53 @@
 	uvmpdpol_estimatepageable(active, inactive);
 }
 
+
+/*
+ * Use a separate thread for draining pools.
+ * This work can't done from the main pagedaemon thread because
+ * some pool allocators need to take vm_map locks.
+ */
+
+static void
+uvmpd_pool_drain_thread(void *arg)
+{
+	int bufcnt;
+
+	for (;;) {
+		mutex_enter(&uvmpd_pool_drain_lock);
+		if (!uvmpd_pool_drain_run) {
+			cv_wait(&uvmpd_pool_drain_cv, &uvmpd_pool_drain_lock);
+		}
+		uvmpd_pool_drain_run = false;
+		mutex_exit(&uvmpd_pool_drain_lock);
+
+		/*
+		 * kill unused metadata buffers.
+		 */
+		mutex_spin_enter(&uvm_fpageqlock);
+		bufcnt = uvmexp.freetarg - uvmexp.free;
+		mutex_spin_exit(&uvm_fpageqlock);
+		if (bufcnt < 0)
+			bufcnt = 0;
+
+		mutex_enter(&bufcache_lock);
+		buf_drain(bufcnt << PAGE_SHIFT);
+		mutex_exit(&bufcache_lock);
+
+		/*
+		 * drain a pool.
+		 */
+		pool_drain(NULL);
+	}
+	/*NOTREACHED*/
+}
+
+static void
+uvmpd_pool_drain_wakeup(void)
+{
+
+	mutex_enter(&uvmpd_pool_drain_lock);
+	uvmpd_pool_drain_run = true;
+	cv_signal(&uvmpd_pool_drain_cv);
+	mutex_exit(&uvmpd_pool_drain_lock);
+}