Skip to content

Commit

Permalink
mm/mmap: remove __vma_adjust()
Browse files Browse the repository at this point in the history 
Inline the work of __vma_adjust() into vma_merge().  This reduces code
size and has the added benefits of the comments for the cases being
located with the code.

Change the comments referencing vma_adjust() accordingly.

[Liam.Howlett@oracle.com: fix vma_merge() offset when expanding the next vma]
  Link: https://lkml.kernel.org/r/20230130195713.2881766-1-Liam.Howlett@oracle.com
Link: https://lkml.kernel.org/r/20230120162650.984577-49-Liam.Howlett@oracle.com
Signed-off-by: Liam R. Howlett <Liam.Howlett@oracle.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
  • Loading branch information
Liam R. Howlett authored and Andrew Morton committed Feb 10, 2023
1 parent 287051b commit 0503ea8
Show file tree
Hide file tree
Showing 4 changed files with 107 additions and 162 deletions.
2 changes: 1 addition & 1 deletion kernel/events/uprobes.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -1351,7 +1351,7 @@ static int delayed_ref_ctr_inc(struct vm_area_struct *vma)
}

/*
* Called from mmap_region/vma_adjust with mm->mmap_lock acquired.
* Called from mmap_region/vma_merge with mm->mmap_lock acquired.
*
* Currently we ignore all errors and always return 0, the callers
* can't handle the failure anyway.
Expand Down
2 changes: 1 addition & 1 deletion mm/filemap.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -97,7 +97,7 @@
* ->i_pages lock (__sync_single_inode)
*
* ->i_mmap_rwsem
* ->anon_vma.lock (vma_adjust)
* ->anon_vma.lock (vma_merge)
*
* ->anon_vma.lock
* ->page_table_lock or pte_lock (anon_vma_prepare and various)
Expand Down
250 changes: 97 additions & 153 deletions mm/mmap.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -740,133 +740,6 @@ int vma_shrink(struct vma_iterator *vmi, struct vm_area_struct *vma,
return 0;
}

/*
* We cannot adjust vm_start, vm_end, vm_pgoff fields of a vma that
* is already present in an i_mmap tree without adjusting the tree.
* The following helper function should be used when such adjustments
* are necessary. The "insert" vma (if any) is to be inserted
* before we drop the necessary locks.
*/
int __vma_adjust(struct vma_iterator *vmi, struct vm_area_struct *vma,
unsigned long start, unsigned long end, pgoff_t pgoff,
struct vm_area_struct *expand)
{
struct mm_struct *mm = vma->vm_mm;
struct vm_area_struct *remove2 = NULL;
struct vm_area_struct *remove = NULL;
struct vm_area_struct *next = find_vma(mm, vma->vm_end);
struct vm_area_struct *orig_vma = vma;
struct file *file = vma->vm_file;
bool vma_changed = false;
long adjust_next = 0;
struct vma_prepare vma_prep;

if (next) {
int error = 0;

if (end >= next->vm_end) {
/*
* vma expands, overlapping all the next, and
* perhaps the one after too (mprotect case 6).
* The only other cases that gets here are
* case 1, case 7 and case 8.
*/
if (next == expand) {
/*
* The only case where we don't expand "vma"
* and we expand "next" instead is case 8.
*/
VM_WARN_ON(end != next->vm_end);
/*
* we're removing "vma" and that to do so we
* swapped "vma" and "next".
*/
VM_WARN_ON(file != next->vm_file);
swap(vma, next);
remove = next;
} else {
VM_WARN_ON(expand != vma);
/*
* case 1, 6, 7, remove next.
* case 6 also removes the one beyond next
*/
remove = next;
if (end > next->vm_end)
remove2 = find_vma(mm, next->vm_end);

VM_WARN_ON(remove2 != NULL &&
end != remove2->vm_end);
}

/*
* If next doesn't have anon_vma, import from vma after
* next, if the vma overlaps with it.
*/
if (remove != NULL && !next->anon_vma)
error = dup_anon_vma(vma, remove2);
else
error = dup_anon_vma(vma, remove);

} else if (end > next->vm_start) {
/*
* vma expands, overlapping part of the next:
* mprotect case 5 shifting the boundary up.
*/
adjust_next = (end - next->vm_start);
VM_WARN_ON(expand != vma);
error = dup_anon_vma(vma, next);
} else if (end < vma->vm_end) {
/*
* vma shrinks, and !insert tells it's not
* split_vma inserting another: so it must be
* mprotect case 4 shifting the boundary down.
*/
adjust_next = -(vma->vm_end - end);
VM_WARN_ON(expand != next);
error = dup_anon_vma(next, vma);
}
if (error)
return error;
}

if (vma_iter_prealloc(vmi))
return -ENOMEM;

vma_adjust_trans_huge(orig_vma, start, end, adjust_next);

init_multi_vma_prep(&vma_prep, vma, adjust_next ? next : NULL, remove,
remove2);
VM_WARN_ON(vma_prep.anon_vma && adjust_next && next->anon_vma &&
vma_prep.anon_vma != next->anon_vma);

vma_prepare(&vma_prep);

if (start < vma->vm_start || end > vma->vm_end)
vma_changed = true;

vma->vm_start = start;
vma->vm_end = end;
vma->vm_pgoff = pgoff;

if (vma_changed)
vma_iter_store(vmi, vma);

if (adjust_next) {
next->vm_start += adjust_next;
next->vm_pgoff += adjust_next >> PAGE_SHIFT;
if (adjust_next < 0) {
WARN_ON_ONCE(vma_changed);
vma_iter_store(vmi, next);
}
}

vma_complete(&vma_prep, vmi, mm);
vma_iter_free(vmi);
validate_mm(mm);

return 0;
}

/*
* If the vma has a ->close operation then the driver probably needs to release
* per-vma resources, so we don't attempt to merge those.
Expand Down Expand Up @@ -993,7 +866,7 @@ can_vma_merge_after(struct vm_area_struct *vma, unsigned long vm_flags,
* It is important for case 8 that the vma NNNN overlapping the
* region AAAA is never going to extended over XXXX. Instead XXXX must
* be extended in region AAAA and NNNN must be removed. This way in
* all cases where vma_merge succeeds, the moment vma_adjust drops the
* all cases where vma_merge succeeds, the moment vma_merge drops the
* rmap_locks, the properties of the merged vma will be already
* correct for the whole merged range. Some of those properties like
* vm_page_prot/vm_flags may be accessed by rmap_walks and they must
Expand All @@ -1003,6 +876,12 @@ can_vma_merge_after(struct vm_area_struct *vma, unsigned long vm_flags,
* or other rmap walkers (if working on addresses beyond the "end"
* parameter) may establish ptes with the wrong permissions of NNNN
* instead of the right permissions of XXXX.
*
* In the code below:
* PPPP is represented by *prev
* NNNN is represented by *mid (and possibly equal to *next)
* XXXX is represented by *next or not represented at all.
* AAAA is not represented - it will be merged or the function will return NULL
*/
struct vm_area_struct *vma_merge(struct vma_iterator *vmi, struct mm_struct *mm,
struct vm_area_struct *prev, unsigned long addr,
Expand All @@ -1013,11 +892,19 @@ struct vm_area_struct *vma_merge(struct vma_iterator *vmi, struct mm_struct *mm,
struct anon_vma_name *anon_name)
{
pgoff_t pglen = (end - addr) >> PAGE_SHIFT;
pgoff_t vma_pgoff;
struct vm_area_struct *mid, *next, *res = NULL;
struct vm_area_struct *vma, *adjust, *remove, *remove2;
int err = -1;
bool merge_prev = false;
bool merge_next = false;
bool vma_expanded = false;
struct vma_prepare vp;
unsigned long vma_end = end;
long adj_next = 0;
unsigned long vma_start = addr;

validate_mm(mm);
/*
* We later require that vma->vm_flags == vm_flags,
* so this tests vma->vm_flags & VM_SPECIAL, too.
Expand All @@ -1035,13 +922,17 @@ struct vm_area_struct *vma_merge(struct vma_iterator *vmi, struct mm_struct *mm,
VM_WARN_ON(mid && end > mid->vm_end);
VM_WARN_ON(addr >= end);

/* Can we merge the predecessor? */
if (prev && prev->vm_end == addr &&
mpol_equal(vma_policy(prev), policy) &&
can_vma_merge_after(prev, vm_flags,
anon_vma, file, pgoff,
vm_userfaultfd_ctx, anon_name)) {
merge_prev = true;
if (prev) {
res = prev;
vma = prev;
vma_start = prev->vm_start;
vma_pgoff = prev->vm_pgoff;
/* Can we merge the predecessor? */
if (prev->vm_end == addr && mpol_equal(vma_policy(prev), policy)
&& can_vma_merge_after(prev, vm_flags, anon_vma, file,
pgoff, vm_userfaultfd_ctx, anon_name)) {
merge_prev = true;
}
}
/* Can we merge the successor? */
if (next && end == next->vm_start &&
Expand All @@ -1051,32 +942,85 @@ struct vm_area_struct *vma_merge(struct vma_iterator *vmi, struct mm_struct *mm,
vm_userfaultfd_ctx, anon_name)) {
merge_next = true;
}

remove = remove2 = adjust = NULL;
/* Can we merge both the predecessor and the successor? */
if (merge_prev && merge_next &&
is_mergeable_anon_vma(prev->anon_vma,
next->anon_vma, NULL)) { /* cases 1, 6 */
err = __vma_adjust(vmi, prev, prev->vm_start,
next->vm_end, prev->vm_pgoff, prev);
res = prev;
} else if (merge_prev) { /* cases 2, 5, 7 */
err = __vma_adjust(vmi, prev, prev->vm_start,
end, prev->vm_pgoff, prev);
res = prev;
is_mergeable_anon_vma(prev->anon_vma, next->anon_vma, NULL)) {
remove = mid; /* case 1 */
vma_end = next->vm_end;
err = dup_anon_vma(res, remove);
if (mid != next) { /* case 6 */
remove2 = next;
if (!remove->anon_vma)
err = dup_anon_vma(res, remove2);
}
} else if (merge_prev) {
err = 0; /* case 2 */
if (mid && end > mid->vm_start) {
err = dup_anon_vma(res, mid);
if (end == mid->vm_end) { /* case 7 */
remove = mid;
} else { /* case 5 */
adjust = mid;
adj_next = (end - mid->vm_start);
}
}
} else if (merge_next) {
if (prev && addr < prev->vm_end) /* case 4 */
err = __vma_adjust(vmi, prev, prev->vm_start,
addr, prev->vm_pgoff, next);
else /* cases 3, 8 */
err = __vma_adjust(vmi, mid, addr, next->vm_end,
next->vm_pgoff - pglen, next);
res = next;
if (prev && addr < prev->vm_end) { /* case 4 */
vma_end = addr;
adjust = mid;
adj_next = -(vma->vm_end - addr);
err = dup_anon_vma(res, adjust);
} else {
vma = next; /* case 3 */
vma_start = addr;
vma_end = next->vm_end;
vma_pgoff = mid->vm_pgoff;
err = 0;
if (mid != next) { /* case 8 */
remove = mid;
err = dup_anon_vma(res, remove);
}
}
}

/*
* Cannot merge with predecessor or successor or error in __vma_adjust?
*/
/* Cannot merge or error in anon_vma clone */
if (err)
return NULL;

if (vma_iter_prealloc(vmi))
return NULL;

vma_adjust_trans_huge(vma, vma_start, vma_end, adj_next);
init_multi_vma_prep(&vp, vma, adjust, remove, remove2);
VM_WARN_ON(vp.anon_vma && adjust && adjust->anon_vma &&
vp.anon_vma != adjust->anon_vma);

vma_prepare(&vp);
if (vma_start < vma->vm_start || vma_end > vma->vm_end)
vma_expanded = true;

vma->vm_start = vma_start;
vma->vm_end = vma_end;
vma->vm_pgoff = vma_pgoff;

if (vma_expanded)
vma_iter_store(vmi, vma);

if (adj_next) {
adjust->vm_start += adj_next;
adjust->vm_pgoff += adj_next >> PAGE_SHIFT;
if (adj_next < 0) {
WARN_ON(vma_expanded);
vma_iter_store(vmi, next);
}
}

vma_complete(&vp, vmi, mm);
vma_iter_free(vmi);
validate_mm(mm);
khugepaged_enter_vma(res, vm_flags);

if (res)
Expand Down
15 changes: 8 additions & 7 deletions mm/rmap.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -262,11 +262,12 @@ static inline void unlock_anon_vma_root(struct anon_vma *root)
* Attach the anon_vmas from src to dst.
* Returns 0 on success, -ENOMEM on failure.
*
* anon_vma_clone() is called by __vma_adjust(), __split_vma(), copy_vma() and
* anon_vma_fork(). The first three want an exact copy of src, while the last
* one, anon_vma_fork(), may try to reuse an existing anon_vma to prevent
* endless growth of anon_vma. Since dst->anon_vma is set to NULL before call,
* we can identify this case by checking (!dst->anon_vma && src->anon_vma).
* anon_vma_clone() is called by vma_expand(), vma_merge(), __split_vma(),
* copy_vma() and anon_vma_fork(). The first four want an exact copy of src,
* while the last one, anon_vma_fork(), may try to reuse an existing anon_vma to
* prevent endless growth of anon_vma. Since dst->anon_vma is set to NULL before
* call, we can identify this case by checking (!dst->anon_vma &&
* src->anon_vma).
*
* If (!dst->anon_vma && src->anon_vma) is true, this function tries to find
* and reuse existing anon_vma which has no vmas and only one child anon_vma.
Expand Down Expand Up @@ -1253,7 +1254,7 @@ void page_add_anon_rmap(struct page *page, struct vm_area_struct *vma,
__lruvec_stat_mod_folio(folio, NR_ANON_MAPPED, nr);

if (likely(!folio_test_ksm(folio))) {
/* address might be in next vma when migration races vma_adjust */
/* address might be in next vma when migration races vma_merge */
if (first)
__page_set_anon_rmap(folio, page, vma, address,
!!(flags & RMAP_EXCLUSIVE));
Expand Down Expand Up @@ -2524,7 +2525,7 @@ void hugepage_add_anon_rmap(struct page *page, struct vm_area_struct *vma,

BUG_ON(!folio_test_locked(folio));
BUG_ON(!anon_vma);
/* address might be in next vma when migration races vma_adjust */
/* address might be in next vma when migration races vma_merge */
first = atomic_inc_and_test(&folio->_entire_mapcount);
VM_BUG_ON_PAGE(!first && (flags & RMAP_EXCLUSIVE), page);
VM_BUG_ON_PAGE(!first && PageAnonExclusive(page), page);
Expand Down

0 comments on commit 0503ea8

Please sign in to comment.