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Make MAP_NOSYNC handling in the vm_fault() read-locked object path

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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
This commit is contained in:
Konstantin Belousov 2014-10-10 19:27:36 +00:00
parent 1d2baefc13
commit a36f55322c
1 changed files with 67 additions and 41 deletions
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108
sys/vm/vm_fault.c
View File

@ -174,6 +174,70 @@ unlock_and_deallocate(struct faultstate *fs)
}
}
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);
/*