Author: kib
Date: Fri Oct 10 19:27:36 2014
New Revision: 272907
URL: https://svnweb.freebsd.org/changeset/base/272907
Log:
Make MAP_NOSYNC handling in the vm_fault() read-locked object path
compatible with write-locked path. Test for MAP_ENTRY_NOSYNC and set
VPO_NOSYNC for pages with dirty mask zero (this does not exclude a
possibility that the page is dirty, e.g. due to read fault on
writeable mapping and consequent write; the same issue exists in the
slow path).
Use helper vm_fault_dirty() to unify fast and slow path handling of
VPO_NOSYNC and setting the dirty mask.
Reviewed by: alc
Sponsored by: The FreeBSD Foundation
Modified:
head/sys/vm/vm_fault.c
Modified: head/sys/vm/vm_fault.c
==============================================================================
--- head/sys/vm/vm_fault.c Fri Oct 10 19:26:26 2014 (r272906)
+++ head/sys/vm/vm_fault.c Fri Oct 10 19:27:36 2014 (r272907)
@@ -174,6 +174,70 @@ unlock_and_deallocate(struct faultstate
}
}
+static void
+vm_fault_dirty(vm_map_entry_t entry, vm_page_t m, vm_prot_t prot,
+ vm_prot_t fault_type, int fault_flags, boolean_t set_wd)
+{
+ boolean_t need_dirty;
+
+ if (((prot & VM_PROT_WRITE) == 0 &&
+ (fault_flags & VM_FAULT_DIRTY) == 0) ||
+ (m->oflags & VPO_UNMANAGED) != 0)
+ return;
+
+ VM_OBJECT_ASSERT_LOCKED(m->object);
+
+ need_dirty = ((fault_type & VM_PROT_WRITE) != 0 &&
+ (fault_flags & VM_FAULT_CHANGE_WIRING) == 0) ||
+ (fault_flags & VM_FAULT_DIRTY) != 0;
+
+ if (set_wd)
+ vm_object_set_writeable_dirty(m->object);
+ else
+ /*
+ * If two callers of vm_fault_dirty() with set_wd ==
+ * FALSE, one for the map entry with MAP_ENTRY_NOSYNC
+ * flag set, other with flag clear, race, it is
+ * possible for the no-NOSYNC thread to see m->dirty
+ * != 0 and not clear VPO_NOSYNC. Take vm_page lock
+ * around manipulation of VPO_NOSYNC and
+ * vm_page_dirty() call, to avoid the race and keep
+ * m->oflags consistent.
+ */
+ vm_page_lock(m);
+
+ /*
+ * If this is a NOSYNC mmap we do not want to set VPO_NOSYNC
+ * if the page is already dirty to prevent data written with
+ * the expectation of being synced from not being synced.
+ * Likewise if this entry does not request NOSYNC then make
+ * sure the page isn't marked NOSYNC. Applications sharing
+ * data should use the same flags to avoid ping ponging.
+ */
+ if ((entry->eflags & MAP_ENTRY_NOSYNC) != 0) {
+ if (m->dirty == 0) {
+ m->oflags |= VPO_NOSYNC;
+ }
+ } else {
+ m->oflags &= ~VPO_NOSYNC;
+ }
+
+ /*
+ * If the fault is a write, we know that this page is being
+ * written NOW so dirty it explicitly to save on
+ * pmap_is_modified() calls later.
+ *
+ * Also tell the backing pager, if any, that it should remove
+ * any swap backing since the page is now dirty.
+ */
+ if (need_dirty)
+ vm_page_dirty(m);
+ if (!set_wd)
+ vm_page_unlock(m);
+ if (need_dirty)
+ vm_pager_page_unswapped(m);
+}
+
/*
* TRYPAGER - used by vm_fault to calculate whether the pager for the
* current object *might* contain the page.
@@ -321,11 +385,8 @@ RetryFault:;
vm_page_hold(m);
vm_page_unlock(m);
}
- if ((fault_type & VM_PROT_WRITE) != 0 &&
- (m->oflags & VPO_UNMANAGED) == 0) {
- vm_page_dirty(m);
- vm_pager_page_unswapped(m);
- }
+ vm_fault_dirty(fs.entry, m, prot, fault_type, fault_flags,
+ FALSE);
VM_OBJECT_RUNLOCK(fs.first_object);
if (!wired)
vm_fault_prefault(&fs, vaddr, 0, 0);
@@ -898,42 +959,7 @@ vnode_locked:
if (hardfault)
fs.entry->next_read = fs.pindex + faultcount - reqpage;
- if (((prot & VM_PROT_WRITE) != 0 ||
- (fault_flags & VM_FAULT_DIRTY) != 0) &&
- (fs.m->oflags & VPO_UNMANAGED) == 0) {
- vm_object_set_writeable_dirty(fs.object);
-
- /*
- * If this is a NOSYNC mmap we do not want to set VPO_NOSYNC
- * if the page is already dirty to prevent data written with
- * the expectation of being synced from not being synced.
- * Likewise if this entry does not request NOSYNC then make
- * sure the page isn't marked NOSYNC. Applications sharing
- * data should use the same flags to avoid ping ponging.
- */
- if (fs.entry->eflags & MAP_ENTRY_NOSYNC) {
- if (fs.m->dirty == 0)
- fs.m->oflags |= VPO_NOSYNC;
- } else {
- fs.m->oflags &= ~VPO_NOSYNC;
- }
-
- /*
- * If the fault is a write, we know that this page is being
- * written NOW so dirty it explicitly to save on
- * pmap_is_modified() calls later.
- *
- * Also tell the backing pager, if any, that it should remove
- * any swap backing since the page is now dirty.
- */
- if (((fault_type & VM_PROT_WRITE) != 0 &&
- (fault_flags & VM_FAULT_CHANGE_WIRING) == 0) ||
- (fault_flags & VM_FAULT_DIRTY) != 0) {
- vm_page_dirty(fs.m);
- vm_pager_page_unswapped(fs.m);
- }
- }
-
+ vm_fault_dirty(fs.entry, fs.m, prot, fault_type, fault_flags, TRUE);
vm_page_assert_xbusied(fs.m);
/*
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