From 625e38eddc8b523d10948382f838410bcea38748 Mon Sep 17 00:00:00 2001
From: alc <alc@FreeBSD.org>
Date: Sun, 25 Nov 2007 20:37:29 +0000
Subject: [PATCH] Make contigmalloc(9)'s page laundering more robust. 
 Specifically, use vm_pageout_fallback_object_lock() in
 vm_contig_launder_page() to better handle a lock-ordering problem. 
 Consequently, trylock's failure on the page's containing object no longer
 implies that the page cannot be laundered.

MFC after: 6 weeks
---
 sys/vm/vm_contig.c  | 9 ++++++---
 sys/vm/vm_pageout.c | 2 +-
 sys/vm/vm_pageout.h | 1 +
 3 files changed, 8 insertions(+), 4 deletions(-)

diff --git a/sys/vm/vm_contig.c b/sys/vm/vm_contig.c
index 7a6eb5130436..1458e0d8d2f8 100644
--- a/sys/vm/vm_contig.c
+++ b/sys/vm/vm_contig.c
@@ -88,7 +88,7 @@ __FBSDID("$FreeBSD$");
 #include <vm/vm_extern.h>
 
 static int
-vm_contig_launder_page(vm_page_t m)
+vm_contig_launder_page(vm_page_t m, vm_page_t *next)
 {
 	vm_object_t object;
 	vm_page_t m_tmp;
@@ -98,8 +98,11 @@ vm_contig_launder_page(vm_page_t m)
 
 	mtx_assert(&vm_page_queue_mtx, MA_OWNED);
 	object = m->object;
-	if (!VM_OBJECT_TRYLOCK(object))
+	if (!VM_OBJECT_TRYLOCK(object) &&
+	    !vm_pageout_fallback_object_lock(m, next)) {
+		VM_OBJECT_UNLOCK(object);
 		return (EAGAIN);
+	}
 	if (vm_page_sleep_if_busy(m, TRUE, "vpctw0")) {
 		VM_OBJECT_UNLOCK(object);
 		vm_page_lock_queues();
@@ -157,7 +160,7 @@ vm_contig_launder(int queue)
 
 		KASSERT(VM_PAGE_INQUEUE2(m, queue),
 		    ("vm_contig_launder: page %p's queue is not %d", m, queue));
-		error = vm_contig_launder_page(m);
+		error = vm_contig_launder_page(m, &next);
 		if (error == 0)
 			return (TRUE);
 		if (error == EBUSY)
diff --git a/sys/vm/vm_pageout.c b/sys/vm/vm_pageout.c
index d21277b51f4d..f5d4ee7adee4 100644
--- a/sys/vm/vm_pageout.c
+++ b/sys/vm/vm_pageout.c
@@ -230,7 +230,7 @@ static void vm_pageout_page_stats(void);
  * This function depends on both the lock portion of struct vm_object
  * and normal struct vm_page being type stable.
  */
-static boolean_t
+boolean_t
 vm_pageout_fallback_object_lock(vm_page_t m, vm_page_t *next)
 {
 	struct vm_page marker;
diff --git a/sys/vm/vm_pageout.h b/sys/vm/vm_pageout.h
index 1b74fab74f0e..1586ac41475d 100644
--- a/sys/vm/vm_pageout.h
+++ b/sys/vm/vm_pageout.h
@@ -98,6 +98,7 @@ extern void vm_wait(void);
 extern void vm_waitpfault(void);
 
 #ifdef _KERNEL
+boolean_t vm_pageout_fallback_object_lock(vm_page_t, vm_page_t *);
 int vm_pageout_flush(vm_page_t *, int, int);
 #endif
 #endif	/* _VM_VM_PAGEOUT_H_ */