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mm/vma: introduce vma_assert_can_modify()

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vma_assert_write_locked() and vma_assert_attached() are useful for their
own purposes, however VMA code absolutely does allow the modification of
non-write locked VMAs if they are at that point detached (i.e. unreachable
from anywhere).

It's therefore useful to be able to assert that a VMA is either
detached (modification doesn't matter) or write locked (you're explicitly
locked for modification).

Therefore introduce vma_assert_can_modify() for this purpose.

While we're here, make vma_is_attached() available generally - if
!CONFIG_PER_VMA_LOCK, then there's no sense in which a VMA is
detached (vma_mark_detached() is a noop), so have this default to true in
this case.

Also update VMA userland tests to reflect this change, correcting the
previously open-coded vma_assert_[attached,detached]() there.

Link: https://lore.kernel.org/20260710-b4-pre-scalable-cow-v2-22-2a5aa403d977@kernel.org
Signed-off-by: Lorenzo Stoakes <ljs@kernel.org>
Reviewed-by: Gregory Price <gourry@gourry.net>
Reviewed-by: Vlastimil Babka (SUSE) <vbabka@kernel.org>
Cc: Ackerley Tng <ackerleytng@google.com>
Cc: David Hildenbrand (Arm) <david@kernel.org>
Cc: Kai Huang <kai.huang@intel.com>
Cc: Marek Szyprowski <m.szyprowski@samsung.com>
Cc: Pedro Falcato <pfalcato@suse.de>
Cc: SJ Park <sj@kernel.org>
Cc: Thomas Zimmermann <tzimmermann@suse.de>
Cc: Liam R. Howlett (Oracle) <liam@infradead.org>
Cc: Zi Yan <ziy@nvidia.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
This commit is contained in:
Lorenzo Stoakes 2026-07-10 21:17:03 +01:00 committed by Andrew Morton
parent 93d23dff8e
commit e65f4dfac1
2 changed files with 21 additions and 2 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

8
include/linux/mmap_lock.h
View File

@ -506,6 +506,8 @@ static inline __must_check
int vma_start_write_killable(struct vm_area_struct *vma) { return 0; }
static inline void vma_assert_write_locked(struct vm_area_struct *vma)
{ mmap_assert_write_locked(vma->vm_mm); }
static inline bool vma_is_attached(struct vm_area_struct *vma)
{ return true; }
static inline void vma_assert_attached(struct vm_area_struct *vma) {}
static inline void vma_assert_detached(struct vm_area_struct *vma) {}
static inline void vma_mark_attached(struct vm_area_struct *vma) {}
@ -530,6 +532,12 @@ static inline void vma_assert_stabilised(struct vm_area_struct *vma)
#endif /* CONFIG_PER_VMA_LOCK */
static inline void vma_assert_can_modify(struct vm_area_struct *vma)
{
if (vma_is_attached(vma))
vma_assert_write_locked(vma);
}
static inline void mmap_write_lock(struct mm_struct *mm)
{
__mmap_lock_trace_start_locking(mm, true);

15
tools/testing/vma/include/dup.h
View File

@ -1163,6 +1163,11 @@ static inline struct vm_area_struct *vma_next(struct vma_iterator *vmi)
return mas_find(&vmi->mas, ULONG_MAX);
}
static inline bool vma_is_attached(struct vm_area_struct *vma)
{
return refcount_read(&vma->vm_refcnt);
}
/*
* WARNING: to avoid racing with vma_mark_attached()/vma_mark_detached(), these
* assertions should be made either under mmap_write_lock or when the object
@ -1170,12 +1175,12 @@ static inline struct vm_area_struct *vma_next(struct vma_iterator *vmi)
*/
static inline void vma_assert_attached(struct vm_area_struct *vma)
{
WARN_ON_ONCE(!refcount_read(&vma->vm_refcnt));
WARN_ON_ONCE(!vma_is_attached(vma));
}
static inline void vma_assert_detached(struct vm_area_struct *vma)
{
WARN_ON_ONCE(refcount_read(&vma->vm_refcnt));
WARN_ON_ONCE(vma_is_attached(vma));
}
static inline void vma_assert_write_locked(struct vm_area_struct *);
@ -1564,3 +1569,9 @@ static inline pgoff_t linear_page_index(const struct vm_area_struct *vma,
pgoff += vma_start_pgoff(vma);
return pgoff;
}
static inline void vma_assert_can_modify(struct vm_area_struct *vma)
{
if (vma_is_attached(vma))
vma_assert_write_locked(vma);
}