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Date:      Mon, 25 Jul 2022 13:54:54 GMT
From:      Mark Johnston <markj@FreeBSD.org>
To:        src-committers@FreeBSD.org, dev-commits-src-all@FreeBSD.org, dev-commits-src-branches@FreeBSD.org
Subject:   git: d529f396b7e8 - stable/13 - vm_fault: Fix some nits in vm_fault_copy_entry()
Message-ID:  <202207251354.26PDssov019790@gitrepo.freebsd.org>
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The branch stable/13 has been updated by markj:

URL: https://cgit.FreeBSD.org/src/commit/?id=d529f396b7e876cf5bc10bc373376a2b37869d0c

commit d529f396b7e876cf5bc10bc373376a2b37869d0c
Author:     Mark Johnston <markj@FreeBSD.org>
AuthorDate: 2022-07-11 19:27:54 +0000
Commit:     Mark Johnston <markj@FreeBSD.org>
CommitDate: 2022-07-25 13:44:45 +0000

    vm_fault: Fix some nits in vm_fault_copy_entry()
    
    - Correct the description (vm_fault_copy_entry() does not create a
      shadow object).
    - Move some initialization and assertions out of the scope of the object
      locks, when doing so makes sense.
    - Merge a pair of conditional blocks.
    - Use __unused when appropriate.
    
    No functional change intended.
    
    Reviewed by:    alc
    Sponsored by:   The FreeBSD Foundation
    
    (cherry picked from commit b57be759d079d40aa6ec75207faadce5ae1484a2)
---
 sys/vm/vm_fault.c | 51 +++++++++++++++++++++++----------------------------
 1 file changed, 23 insertions(+), 28 deletions(-)

diff --git a/sys/vm/vm_fault.c b/sys/vm/vm_fault.c
index 8981be84b5d2..a6c7a6092f40 100644
--- a/sys/vm/vm_fault.c
+++ b/sys/vm/vm_fault.c
@@ -1952,10 +1952,10 @@ error:
  *	Routine:
  *		vm_fault_copy_entry
  *	Function:
- *		Create new shadow object backing dst_entry with private copy of
- *		all underlying pages. When src_entry is equal to dst_entry,
- *		function implements COW for wired-down map entry. Otherwise,
- *		it forks wired entry into dst_map.
+ *		Create new object backing dst_entry with private copy of all
+ *		underlying pages. When src_entry is equal to dst_entry, function
+ *		implements COW for wired-down map entry. Otherwise, it forks
+ *		wired entry into dst_map.
  *
  *	In/out conditions:
  *		The source and destination maps must be locked for write.
@@ -1963,7 +1963,7 @@ error:
  *		entry corresponding to a main map entry that is wired down).
  */
 void
-vm_fault_copy_entry(vm_map_t dst_map, vm_map_t src_map,
+vm_fault_copy_entry(vm_map_t dst_map, vm_map_t src_map __unused,
     vm_map_entry_t dst_entry, vm_map_entry_t src_entry,
     vm_ooffset_t *fork_charge)
 {
@@ -1973,14 +1973,25 @@ vm_fault_copy_entry(vm_map_t dst_map, vm_map_t src_map,
 	vm_offset_t vaddr;
 	vm_page_t dst_m;
 	vm_page_t src_m;
-	boolean_t upgrade;
-
-#ifdef	lint
-	src_map++;
-#endif	/* lint */
+	bool upgrade;
 
 	upgrade = src_entry == dst_entry;
+	KASSERT(upgrade || dst_entry->object.vm_object == NULL,
+	    ("vm_fault_copy_entry: vm_object not NULL"));
+
+	/*
+	 * If not an upgrade, then enter the mappings in the pmap as
+	 * read and/or execute accesses.  Otherwise, enter them as
+	 * write accesses.
+	 *
+	 * A writeable large page mapping is only created if all of
+	 * the constituent small page mappings are modified. Marking
+	 * PTEs as modified on inception allows promotion to happen
+	 * without taking potentially large number of soft faults.
+	 */
 	access = prot = dst_entry->protection;
+	if (!upgrade)
+		access &= ~VM_PROT_WRITE;
 
 	src_object = src_entry->object.vm_object;
 	src_pindex = OFF_TO_IDX(src_entry->offset);
@@ -2002,16 +2013,13 @@ vm_fault_copy_entry(vm_map_t dst_map, vm_map_t src_map,
 #endif
 		dst_object->domain = src_object->domain;
 		dst_object->charge = dst_entry->end - dst_entry->start;
-	}
 
-	VM_OBJECT_WLOCK(dst_object);
-	KASSERT(upgrade || dst_entry->object.vm_object == NULL,
-	    ("vm_fault_copy_entry: vm_object not NULL"));
-	if (src_object != dst_object) {
 		dst_entry->object.vm_object = dst_object;
 		dst_entry->offset = 0;
 		dst_entry->eflags &= ~MAP_ENTRY_VN_EXEC;
 	}
+
+	VM_OBJECT_WLOCK(dst_object);
 	if (fork_charge != NULL) {
 		KASSERT(dst_entry->cred == NULL,
 		    ("vm_fault_copy_entry: leaked swp charge"));
@@ -2027,19 +2035,6 @@ vm_fault_copy_entry(vm_map_t dst_map, vm_map_t src_map,
 		dst_entry->cred = NULL;
 	}
 
-	/*
-	 * If not an upgrade, then enter the mappings in the pmap as
-	 * read and/or execute accesses.  Otherwise, enter them as
-	 * write accesses.
-	 *
-	 * A writeable large page mapping is only created if all of
-	 * the constituent small page mappings are modified. Marking
-	 * PTEs as modified on inception allows promotion to happen
-	 * without taking potentially large number of soft faults.
-	 */
-	if (!upgrade)
-		access &= ~VM_PROT_WRITE;
-
 	/*
 	 * Loop through all of the virtual pages within the entry's
 	 * range, copying each page from the source object to the

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