svn commit: r310849 - head/sys/vm

[Konstantin Belousov]

Author: kib
Date: Fri Dec 30 18:55:33 2016
New Revision: 310849
URL: https://svnweb.freebsd.org/changeset/base/310849

Log:
  Fix two similar bugs in the populate vm_fault() code.
  
  If pager' populate method succeeded, but other thread raced with us
  and modified vm_map, we must unbusy all pages busied by the pager,
  before we retry the whole fault handling.  If pager instantiated more
  pages than fit into the current map entry, we must unbusy the pages
  which are clipped.
  
  Also do some refactoring, clarify comments and use more clear local
  variable names.
  
  Reported and tested by:	kargl, subbsd at gmail.com (previous version)
  Reviewed by:	alc
  Sponsored by:	The FreeBSD Foundation
  MFC after:	2 weeks

Modified:
  head/sys/vm/vm_fault.c

Modified: head/sys/vm/vm_fault.c
==============================================================================
--- head/sys/vm/vm_fault.c	Fri Dec 30 18:51:56 2016	(r310848)
+++ head/sys/vm/vm_fault.c	Fri Dec 30 18:55:33 2016	(r310849)
@@ -304,13 +304,45 @@ vm_fault_restore_map_lock(struct faultst
 	fs->lookup_still_valid = true;
 }
 
+static void
+vm_fault_populate_check_page(vm_page_t m)
+{
+
+	/*
+	 * Check each page to ensure that the pager is obeying the
+	 * interface: the page must be installed in the object, fully
+	 * valid, and exclusively busied.
+	 */
+	MPASS(m != NULL);
+	MPASS(m->valid == VM_PAGE_BITS_ALL);
+	MPASS(vm_page_xbusied(m));
+}
+
+static void
+vm_fault_populate_cleanup(vm_object_t object, vm_pindex_t first,
+    vm_pindex_t last)
+{
+	vm_page_t m;
+	vm_pindex_t pidx;
+
+	VM_OBJECT_ASSERT_WLOCKED(object);
+	MPASS(first <= last);
+	for (pidx = first, m = vm_page_lookup(object, pidx);
+	    pidx <= last; pidx++, m = vm_page_next(m)) {
+		vm_fault_populate_check_page(m);
+		vm_page_lock(m);
+		vm_page_deactivate(m);
+		vm_page_unlock(m);
+		vm_page_xunbusy(m);
+	}
+}
 
 static int
 vm_fault_populate(struct faultstate *fs, vm_offset_t vaddr, vm_prot_t prot,
     int fault_type, int fault_flags, boolean_t wired, vm_page_t *m_hold)
 {
 	vm_page_t m;
-	vm_pindex_t f_first, f_last, pidx;
+	vm_pindex_t map_first, map_last, pager_first, pager_last, pidx;
 	int rv;
 
 	MPASS(fs->object == fs->first_object);
@@ -319,8 +351,8 @@ vm_fault_populate(struct faultstate *fs,
 	MPASS(fs->first_object->backing_object == NULL);
 	MPASS(fs->lookup_still_valid);
 
-	f_first = OFF_TO_IDX(fs->entry->offset);
-	f_last = OFF_TO_IDX(fs->entry->offset + fs->entry->end -
+	pager_first = OFF_TO_IDX(fs->entry->offset);
+	pager_last = OFF_TO_IDX(fs->entry->offset + fs->entry->end -
 	    fs->entry->start) - 1;
 	unlock_map(fs);
 	unlock_vp(fs);
@@ -334,7 +366,7 @@ vm_fault_populate(struct faultstate *fs,
 	 * to the driver.
 	 */
 	rv = vm_pager_populate(fs->first_object, fs->first_pindex,
-	    fault_type, fs->entry->max_protection, &f_first, &f_last);
+	    fault_type, fs->entry->max_protection, &pager_first, &pager_last);
 
 	VM_OBJECT_ASSERT_WLOCKED(fs->first_object);
 	if (rv == VM_PAGER_BAD) {
@@ -351,34 +383,40 @@ vm_fault_populate(struct faultstate *fs,
 		return (KERN_FAILURE); /* AKA SIGSEGV */
 
 	/* Ensure that the driver is obeying the interface. */
-	MPASS(f_first <= f_last);
-	MPASS(fs->first_pindex <= f_last);
-	MPASS(fs->first_pindex >= f_first);
-	MPASS(f_last < fs->first_object->size);
+	MPASS(pager_first <= pager_last);
+	MPASS(fs->first_pindex <= pager_last);
+	MPASS(fs->first_pindex >= pager_first);
+	MPASS(pager_last < fs->first_object->size);
 
 	vm_fault_restore_map_lock(fs);
-	if (fs->map->timestamp != fs->map_generation)
+	if (fs->map->timestamp != fs->map_generation) {
+		vm_fault_populate_cleanup(fs->first_object, pager_first,
+		    pager_last);
 		return (KERN_RESOURCE_SHORTAGE); /* RetryFault */
+	}
 
-	/* Clip pager response to fit into the vm_map_entry. */
-	f_first = MAX(OFF_TO_IDX(fs->entry->offset), f_first);
-	f_last = MIN(OFF_TO_IDX(fs->entry->end - fs->entry->start +
-	    fs->entry->offset), f_last);
-
-	pidx = f_first;
-	for (m = vm_page_lookup(fs->first_object, pidx); pidx <= f_last;
-	    pidx++, m = vm_page_next(m)) {
-		/*
-		 * Check each page to ensure that the driver is
-		 * obeying the interface: the page must be installed
-		 * in the object, fully valid, and exclusively busied.
-		 */
-		MPASS(m != NULL);
-		MPASS(vm_page_xbusied(m));
-		MPASS(m->valid == VM_PAGE_BITS_ALL);
-		MPASS(m->object == fs->first_object);
-		MPASS(m->pindex == pidx);
-
+	/*
+	 * The map is unchanged after our last unlock.  Process the fault.
+	 *
+	 * The range [pager_first, pager_last] that is given to the
+	 * pager is only a hint.  The pager may populate any range
+	 * within the object that includes the requested page index.
+	 * In case the pager expanded the range, clip it to fit into
+	 * the map entry.
+	 */
+	map_first = MAX(OFF_TO_IDX(fs->entry->offset), pager_first);
+	if (map_first > pager_first)
+		vm_fault_populate_cleanup(fs->first_object, pager_first,
+		    map_first - 1);
+	map_last = MIN(OFF_TO_IDX(fs->entry->end - fs->entry->start +
+	    fs->entry->offset), pager_last);
+	if (map_last < pager_last)
+		vm_fault_populate_cleanup(fs->first_object, map_last + 1,
+		    pager_last);
+
+	for (pidx = map_first, m = vm_page_lookup(fs->first_object, pidx);
+	    pidx <= map_last; pidx++, m = vm_page_next(m)) {
+		vm_fault_populate_check_page(m);
 		vm_fault_dirty(fs->entry, m, prot, fault_type, fault_flags,
 		    true);
 		VM_OBJECT_WUNLOCK(fs->first_object);