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Account the writeable shared mappings backed by file in the vnode

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v_writecount.  Keep the amount of the virtual address space used by
the mappings in the new vm_object un_pager.vnp.writemappings
counter. The vnode v_writecount is incremented when writemappings gets
non-zero value, and decremented when writemappings is returned to
zero.

Writeable shared vnode-backed mappings are accounted for in vm_mmap(),
and vm_map_insert() is instructed to set MAP_ENTRY_VN_WRITECNT flag on
the created map entry.  During deferred map entry deallocation,
vm_map_process_deferred() checks for MAP_ENTRY_VN_WRITECOUNT and
decrements writemappings for the vm object.

Now, the writeable mount cannot be demoted to read-only while
writeable shared mappings of the vnodes from the mount point
exist. Also, execve(2) fails for such files with ETXTBUSY, as it
should be.

Noted by:	tegge
Reviewed by:	tegge (long time ago, early version), alc
Tested by:	pho
MFC after:	3 weeks
This commit is contained in:
Konstantin Belousov 2012-02-23 21:07:16 +00:00
parent 47190ea664
commit 84110e7e0b
Notes: svn2git 2020-12-20 02:59:44 +00:00 
svn path=/head/; revision=232071
6 changed files with 204 additions and 15 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

77
sys/vm/vm_map.c
View File

@ -91,6 +91,7 @@ __FBSDID("$FreeBSD$");
#include <vm/vm_pager.h>
#include <vm/vm_kern.h>
#include <vm/vm_extern.h>
#include <vm/vnode_pager.h>
#include <vm/swap_pager.h>
#include <vm/uma.h>
@ -475,11 +476,23 @@ vm_map_process_deferred(void)
{
struct thread *td;
vm_map_entry_t entry;
vm_object_t object;
td = curthread;
while ((entry = td->td_map_def_user) != NULL) {
td->td_map_def_user = entry->next;
if ((entry->eflags & MAP_ENTRY_VN_WRITECNT) != 0) {
/*
* Decrement the object's writemappings and
* possibly the vnode's v_writecount.
*/
KASSERT((entry->eflags & MAP_ENTRY_IS_SUB_MAP) == 0,
("Submap with writecount"));
object = entry->object.vm_object;
KASSERT(object != NULL, ("No object for writecount"));
vnode_pager_release_writecount(object, entry->start,
entry->end);
}
vm_map_entry_deallocate(entry, FALSE);
}
}
@ -1174,6 +1187,8 @@ vm_map_insert(vm_map_t map, vm_object_t object, vm_ooffset_t offset,
protoeflags |= MAP_ENTRY_NOSYNC;
if (cow & MAP_DISABLE_COREDUMP)
protoeflags |= MAP_ENTRY_NOCOREDUMP;
if (cow & MAP_VN_WRITECOUNT)
protoeflags |= MAP_ENTRY_VN_WRITECNT;
if (cow & MAP_INHERIT_SHARE)
inheritance = VM_INHERIT_SHARE;
else
@ -1516,6 +1531,11 @@ vm_map_simplify_entry(vm_map_t map, vm_map_entry_t entry)
* references. Thus, the map lock can be kept
* without causing a lock-order reversal with
* the vnode lock.
*
* Since we count the number of virtual page
* mappings in object->un_pager.vnp.writemappings,
* the writemappings value should not be adjusted
* when the entry is disposed of.
*/
if (prev->object.vm_object)
vm_object_deallocate(prev->object.vm_object);
@ -1627,6 +1647,13 @@ _vm_map_clip_start(vm_map_t map, vm_map_entry_t entry, vm_offset_t start)
if ((entry->eflags & MAP_ENTRY_IS_SUB_MAP) == 0) {
vm_object_reference(new_entry->object.vm_object);
/*
* The object->un_pager.vnp.writemappings for the
* object of MAP_ENTRY_VN_WRITECNT type entry shall be
* kept as is here. The virtual pages are
* re-distributed among the clipped entries, so the sum is
* left the same.
*/
}
}
@ -2900,6 +2927,7 @@ vm_map_copy_entry(
vm_ooffset_t *fork_charge)
{
vm_object_t src_object;
vm_map_entry_t fake_entry;
vm_offset_t size;
struct ucred *cred;
int charged;
@ -2965,6 +2993,27 @@ vm_map_copy_entry(
src_entry->eflags |= (MAP_ENTRY_COW|MAP_ENTRY_NEEDS_COPY);
dst_entry->eflags |= (MAP_ENTRY_COW|MAP_ENTRY_NEEDS_COPY);
dst_entry->offset = src_entry->offset;
if (src_entry->eflags & MAP_ENTRY_VN_WRITECNT) {
/*
* MAP_ENTRY_VN_WRITECNT cannot
* indicate write reference from
* src_entry, since the entry is
* marked as needs copy. Allocate a
* fake entry that is used to
* decrement object->un_pager.vnp.writecount
* at the appropriate time. Attach
* fake_entry to the deferred list.
*/
fake_entry = vm_map_entry_create(dst_map);
fake_entry->eflags = MAP_ENTRY_VN_WRITECNT;
src_entry->eflags &= ~MAP_ENTRY_VN_WRITECNT;
vm_object_reference(src_object);
fake_entry->object.vm_object = src_object;
fake_entry->start = src_entry->start;
fake_entry->end = src_entry->end;
fake_entry->next = curthread->td_map_def_user;
curthread->td_map_def_user = fake_entry;
}
} else {
dst_entry->object.vm_object = NULL;
dst_entry->offset = 0;
@ -3043,6 +3092,7 @@ vmspace_fork(struct vmspace *vm1, vm_ooffset_t *fork_charge)
vm_map_lock(old_map);
if (old_map->busy)
vm_map_wait_busy(old_map);
new_map = NULL; /* silence gcc */
vm2 = vmspace_alloc(old_map->min_offset, old_map->max_offset);
if (vm2 == NULL)
goto unlock_and_return;
@ -3122,6 +3172,16 @@ vmspace_fork(struct vmspace *vm1, vm_ooffset_t *fork_charge)
new_entry->eflags &= ~(MAP_ENTRY_USER_WIRED |
MAP_ENTRY_IN_TRANSITION);
new_entry->wired_count = 0;
if (new_entry->eflags & MAP_ENTRY_VN_WRITECNT) {
object = new_entry->object.vm_object;
KASSERT(((struct vnode *)object->handle)->
v_writecount > 0,
("vmspace_fork: v_writecount"));
KASSERT(object->un_pager.vnp.writemappings > 0,
("vmspace_fork: vnp.writecount"));
vnode_pager_update_writecount(object,
new_entry->start, new_entry->end);
}
/*
* Insert the entry into the new map -- we know we're
@ -3146,8 +3206,11 @@ vmspace_fork(struct vmspace *vm1, vm_ooffset_t *fork_charge)
*/
new_entry = vm_map_entry_create(new_map);
*new_entry = *old_entry;
/*
* Copied entry is COW over the old object.
*/
new_entry->eflags &= ~(MAP_ENTRY_USER_WIRED |
MAP_ENTRY_IN_TRANSITION);
MAP_ENTRY_IN_TRANSITION | MAP_ENTRY_VN_WRITECNT);
new_entry->wired_count = 0;
new_entry->object.vm_object = NULL;
new_entry->cred = NULL;
@ -3161,9 +3224,15 @@ vmspace_fork(struct vmspace *vm1, vm_ooffset_t *fork_charge)
old_entry = old_entry->next;
}
unlock_and_return:
vm_map_unlock(old_map);
/*
* Use inlined vm_map_unlock() to postpone handling the deferred
* map entries, which cannot be done until both old_map and
* new_map locks are released.
*/
sx_xunlock(&old_map->lock);
if (vm2 != NULL)
vm_map_unlock(new_map);
sx_xunlock(&new_map->lock);
vm_map_process_deferred();
return (vm2);
}

2
sys/vm/vm_map.h
View File

@ -139,6 +139,7 @@ struct vm_map_entry {
#define MAP_ENTRY_GROWS_UP 0x2000 /* Bottom-up stacks */
#define MAP_ENTRY_WIRE_SKIPPED 0x4000
#define MAP_ENTRY_VN_WRITECNT 0x8000 /* writeable vnode mapping */
#ifdef _KERNEL
static __inline u_char
@ -315,6 +316,7 @@ long vmspace_wired_count(struct vmspace *vmspace);
#define MAP_DISABLE_SYNCER 0x0020
#define MAP_DISABLE_COREDUMP 0x0100
#define MAP_PREFAULT_MADVISE 0x0200 /* from (user) madvise request */
#define MAP_VN_WRITECOUNT 0x0400
#define MAP_STACK_GROWS_DOWN 0x1000
#define MAP_STACK_GROWS_UP 0x2000
#define MAP_ACC_CHARGED 0x4000

50
sys/vm/vm_mmap.c
View File

@ -81,6 +81,7 @@ __FBSDID("$FreeBSD$");
#include <vm/vm_pageout.h>
#include <vm/vm_extern.h>
#include <vm/vm_page.h>
#include <vm/vnode_pager.h>
#ifdef HWPMC_HOOKS
#include <sys/pmckern.h>
@ -93,7 +94,7 @@ struct sbrk_args {
#endif
static int vm_mmap_vnode(struct thread *, vm_size_t, vm_prot_t, vm_prot_t *,
int *, struct vnode *, vm_ooffset_t *, vm_object_t *);
int *, struct vnode *, vm_ooffset_t *, vm_object_t *, boolean_t *);
static int vm_mmap_cdev(struct thread *, vm_size_t, vm_prot_t, vm_prot_t *,
int *, struct cdev *, vm_ooffset_t *, vm_object_t *);
static int vm_mmap_shm(struct thread *, vm_size_t, vm_prot_t, vm_prot_t *,
@ -1218,28 +1219,33 @@ sys_munlock(td, uap)
/*
* vm_mmap_vnode()
*
* MPSAFE
*
* Helper function for vm_mmap. Perform sanity check specific for mmap
* operations on vnodes.
*
* For VCHR vnodes, the vnode lock is held over the call to
* vm_mmap_cdev() to keep vp->v_rdev valid.
*/
int
vm_mmap_vnode(struct thread *td, vm_size_t objsize,
vm_prot_t prot, vm_prot_t *maxprotp, int *flagsp,
struct vnode *vp, vm_ooffset_t *foffp, vm_object_t *objp)
struct vnode *vp, vm_ooffset_t *foffp, vm_object_t *objp,
boolean_t *writecounted)
{
struct vattr va;
vm_object_t obj;
vm_offset_t foff;
struct mount *mp;
struct ucred *cred;
int error, flags;
int vfslocked;
int error, flags, locktype, vfslocked;
mp = vp->v_mount;
cred = td->td_ucred;
if ((*maxprotp & VM_PROT_WRITE) && (*flagsp & MAP_SHARED))
locktype = LK_EXCLUSIVE;
else
locktype = LK_SHARED;
vfslocked = VFS_LOCK_GIANT(mp);
if ((error = vget(vp, LK_SHARED, td)) != 0) {
if ((error = vget(vp, locktype, td)) != 0) {
VFS_UNLOCK_GIANT(vfslocked);
return (error);
}
@ -1256,8 +1262,20 @@ vm_mmap_vnode(struct thread *td, vm_size_t objsize,
}
if (obj->handle != vp) {
vput(vp);
vp = (struct vnode*)obj->handle;
vget(vp, LK_SHARED, td);
vp = (struct vnode *)obj->handle;
/*
* Bypass filesystems obey the mpsafety of the
* underlying fs.
*/
error = vget(vp, locktype, td);
if (error != 0) {
VFS_UNLOCK_GIANT(vfslocked);
return (error);
}
if (locktype == LK_EXCLUSIVE) {
*writecounted = TRUE;
vnode_pager_update_writecount(obj, 0, objsize);
}
}
} else if (vp->v_type == VCHR) {
error = vm_mmap_cdev(td, objsize, prot, maxprotp, flagsp,
@ -1293,7 +1311,7 @@ vm_mmap_vnode(struct thread *td, vm_size_t objsize,
objsize = round_page(va.va_size);
if (va.va_nlink == 0)
flags |= MAP_NOSYNC;
obj = vm_pager_allocate(OBJT_VNODE, vp, objsize, prot, foff, td->td_ucred);
obj = vm_pager_allocate(OBJT_VNODE, vp, objsize, prot, foff, cred);
if (obj == NULL) {
error = ENOMEM;
goto done;
@ -1432,6 +1450,7 @@ vm_mmap(vm_map_t map, vm_offset_t *addr, vm_size_t size, vm_prot_t prot,
int rv = KERN_SUCCESS;
int docow, error;
struct thread *td = curthread;
boolean_t writecounted;
if (size == 0)
return (0);
@ -1470,6 +1489,8 @@ vm_mmap(vm_map_t map, vm_offset_t *addr, vm_size_t size, vm_prot_t prot,
return (EINVAL);
fitit = FALSE;
}
writecounted = FALSE;
/*
* Lookup/allocate object.
*/
@ -1480,7 +1501,7 @@ vm_mmap(vm_map_t map, vm_offset_t *addr, vm_size_t size, vm_prot_t prot,
break;
case OBJT_VNODE:
error = vm_mmap_vnode(td, size, prot, &maxprot, &flags,
handle, &foff, &object);
handle, &foff, &object, &writecounted);
break;
case OBJT_SWAP:
error = vm_mmap_shm(td, size, prot, &maxprot, &flags,
@ -1520,6 +1541,8 @@ vm_mmap(vm_map_t map, vm_offset_t *addr, vm_size_t size, vm_prot_t prot,
/* Shared memory is also shared with children. */
if (flags & MAP_SHARED)
docow |= MAP_INHERIT_SHARE;
if (writecounted)
docow |= MAP_VN_WRITECOUNT;
if (flags & MAP_STACK)
rv = vm_map_stack(map, *addr, size, prot, maxprot,
@ -1537,7 +1560,12 @@ vm_mmap(vm_map_t map, vm_offset_t *addr, vm_size_t size, vm_prot_t prot,
* Lose the object reference. Will destroy the
* object if it's an unnamed anonymous mapping
* or named anonymous without other references.
*
* If this mapping was accounted for in the vnode's
* writecount, then undo that now.
*/
if (writecounted)
vnode_pager_release_writecount(object, 0, size);
vm_object_deallocate(object);
}

1
sys/vm/vm_object.h
View File

@ -112,6 +112,7 @@ struct vm_object {
*/
struct {
off_t vnp_size;
vm_ooffset_t writemappings;
} vnp;
/*

85
sys/vm/vnode_pager.c
View File

@ -222,6 +222,7 @@ vnode_pager_alloc(void *handle, vm_ooffset_t size, vm_prot_t prot,
object = vm_object_allocate(OBJT_VNODE, OFF_TO_IDX(round_page(size)));
object->un_pager.vnp.vnp_size = size;
object->un_pager.vnp.writemappings = 0;
object->handle = handle;
VI_LOCK(vp);
@ -268,10 +269,16 @@ vnode_pager_dealloc(object)
wakeup(object);
}
ASSERT_VOP_ELOCKED(vp, "vnode_pager_dealloc");
if (object->un_pager.vnp.writemappings > 0) {
object->un_pager.vnp.writemappings = 0;
vp->v_writecount--;
}
vp->v_object = NULL;
vp->v_vflag &= ~VV_TEXT;
VM_OBJECT_UNLOCK(object);
while (refs-- > 0)
vunref(vp);
VM_OBJECT_LOCK(object);
}
static boolean_t
@ -1215,3 +1222,81 @@ vnode_pager_undirty_pages(vm_page_t *ma, int *rtvals, int written)
}
VM_OBJECT_UNLOCK(obj);
}
void
vnode_pager_update_writecount(vm_object_t object, vm_offset_t start,
vm_offset_t end)
{
struct vnode *vp;
vm_ooffset_t old_wm;
VM_OBJECT_LOCK(object);
if (object->type != OBJT_VNODE) {
VM_OBJECT_UNLOCK(object);
return;
}
old_wm = object->un_pager.vnp.writemappings;
object->un_pager.vnp.writemappings += (vm_ooffset_t)end - start;
vp = object->handle;
if (old_wm == 0 && object->un_pager.vnp.writemappings != 0) {
ASSERT_VOP_ELOCKED(vp, "v_writecount inc");
vp->v_writecount++;
} else if (old_wm != 0 && object->un_pager.vnp.writemappings == 0) {
ASSERT_VOP_ELOCKED(vp, "v_writecount dec");
vp->v_writecount--;
}
VM_OBJECT_UNLOCK(object);
}
void
vnode_pager_release_writecount(vm_object_t object, vm_offset_t start,
vm_offset_t end)
{
struct vnode *vp;
struct mount *mp;
vm_offset_t inc;
int vfslocked;
VM_OBJECT_LOCK(object);
/*
* First, recheck the object type to account for the race when
* the vnode is reclaimed.
*/
if (object->type != OBJT_VNODE) {
VM_OBJECT_UNLOCK(object);
return;
}
/*
* Optimize for the case when writemappings is not going to
* zero.
*/
inc = end - start;
if (object->un_pager.vnp.writemappings != inc) {
object->un_pager.vnp.writemappings -= inc;
VM_OBJECT_UNLOCK(object);
return;
}
vp = object->handle;
vhold(vp);
VM_OBJECT_UNLOCK(object);
vfslocked = VFS_LOCK_GIANT(vp->v_mount);
mp = NULL;
vn_start_write(vp, &mp, V_WAIT);
vn_lock(vp, LK_EXCLUSIVE | LK_RETRY);
/*
* Decrement the object's writemappings, by swapping the start
* and end arguments for vnode_pager_update_writecount(). If
* there was not a race with vnode reclaimation, then the
* vnode's v_writecount is decremented.
*/
vnode_pager_update_writecount(object, end, start);
VOP_UNLOCK(vp, 0);
vdrop(vp);
if (mp != NULL)
vn_finished_write(mp);
VFS_UNLOCK_GIANT(vfslocked);
}

4
sys/vm/vnode_pager.h
View File

@ -46,7 +46,11 @@ int vnode_pager_generic_putpages(struct vnode *vp, vm_page_t *m,
int count, boolean_t sync,
int *rtvals);
void vnode_pager_release_writecount(vm_object_t object, vm_offset_t start,
vm_offset_t end);
void vnode_pager_undirty_pages(vm_page_t *ma, int *rtvals, int written);
void vnode_pager_update_writecount(vm_object_t object, vm_offset_t start,
vm_offset_t end);
#endif /* _KERNEL */
#endif /* _VNODE_PAGER_ */