[PATCH v4 2/4] mm: replace vma_start_write() with vma_start_write_killable()

Suren Baghdasaryan
2026-03-22T05:43:37Z

Now that we have vma_start_write_killable() we can replace most of the
vma_start_write() calls with it, improving reaction time to the kill
signal.

There are several places which are left untouched by this patch:

1. free_pgtables() because function should free page tables even if a
fatal signal is pending.

2. process_vma_walk_lock(), which requires changes in its callers and
will be handled in the next patch.

3. userfaultd code, where some paths calling vma_start_write() can
handle EINTR and some can't without a deeper code refactoring.

4. mpol_rebind_mm() which is used by cpuset controller for migrations
and operates on a remote mm. Incomplete operations here would result
in an inconsistent cgroup state.

5. vm_flags_{set|mod|clear} require refactoring that involves moving
vma_start_write() out of these functions and replacing it with
vma_assert_write_locked(), then callers of these functions should
lock the vma themselves using vma_start_write_killable() whenever
possible.

In a number of places we now lock VMA earlier than before to avoid
doing work and undoing it later if a fatal signal is pending. This
is safe because the moves are happening within sections where we
already hold the mmap_write_lock, so the moves do not change the
locking order relative to other kernel locks.

Suggested-by: Matthew Wilcox <willy@infradead.org>
Signed-off-by: Suren Baghdasaryan <surenb@google.com>
Reviewed-by: Ritesh Harjani (IBM) <ritesh.list@gmail.com> # powerpc
---
arch/powerpc/kvm/book3s_hv_uvmem.c | 5 +-
mm/khugepaged.c | 5 +-
mm/madvise.c | 4 +-
mm/memory.c | 2 +
mm/mempolicy.c | 12 ++-
mm/mlock.c | 28 +++++--
mm/mprotect.c | 5 +-
mm/mremap.c | 4 +-
mm/vma.c | 117 +++++++++++++++++++++--------
mm/vma_exec.c | 6 +-
10 files changed, 142 insertions(+), 46 deletions(-)

diff --git a/arch/powerpc/kvm/book3s_hv_uvmem.c b/arch/powerpc/kvm/book3s_hv_uvmem.c
index 5fbb95d90e99..0a28b48a46b8 100644
--- a/arch/powerpc/kvm/book3s_hv_uvmem.c
+++ b/arch/powerpc/kvm/book3s_hv_uvmem.c
@@ -410,7 +410,10 @@ static int kvmppc_memslot_page_merge(struct kvm *kvm,
ret = H_STATE;
break;
}
- vma_start_write(vma);
+ if (vma_start_write_killable(vma)) {
+ ret = H_STATE;
+ break;
+ }
/* Copy vm_flags to avoid partial modifications in ksm_madvise */
vm_flags = vma->vm_flags;
ret = ksm_madvise(vma, vma->vm_start, vma->vm_end,
diff --git a/mm/khugepaged.c b/mm/khugepaged.c
index 4b0e59c7c0e6..e2f263076084 100644
--- a/mm/khugepaged.c
+++ b/mm/khugepaged.c
@@ -1159,7 +1159,10 @@ static enum scan_result collapse_huge_page(struct mm_struct *mm, unsigned long a
if (result != SCAN_SUCCEED)
goto out_up_write;
/* check if the pmd is still valid */
- vma_start_write(vma);
+ if (vma_start_write_killable(vma)) {
+ result = SCAN_FAIL;
+ goto out_up_write;
+ }
result = check_pmd_still_valid(mm, address, pmd);
if (result != SCAN_SUCCEED)
goto out_up_write;
diff --git a/mm/madvise.c b/mm/madvise.c
index 69708e953cf5..feaa16b0e1dc 100644
--- a/mm/madvise.c
+++ b/mm/madvise.c
@@ -175,7 +175,9 @@ static int madvise_update_vma(vm_flags_t new_flags,
madv_behavior->vma = vma;

/* vm_flags is protected by the mmap_lock held in write mode. */
- vma_start_write(vma);
+ if (vma_start_write_killable(vma))
+ return -EINTR;
+
vma->flags = new_vma_flags;
if (set_new_anon_name)
return replace_anon_vma_name(vma, anon_name);
diff --git a/mm/memory.c b/mm/memory.c
index 68cc592ff0ba..b930459e32ec 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -366,6 +366,8 @@ void free_pgd_range(struct mmu_gather *tlb,
* page tables that should be removed. This can differ from the vma mappings on
* some archs that may have mappings that need to be removed outside the vmas.
* Note that the prev->vm_end and next->vm_start are often used.
+ * We don't use vma_start_write_killable() because page tables should be freed
+ * even if the task is being killed.
*
* The vma_end differs from the pg_end when a dup_mmap() failed and the tree has
* unrelated data to the mm_struct being torn down.
diff --git a/mm/mempolicy.c b/mm/mempolicy.c
index e5528c35bbb8..929e843543cf 100644
--- a/mm/mempolicy.c
+++ b/mm/mempolicy.c
@@ -1784,7 +1784,8 @@ SYSCALL_DEFINE4(set_mempolicy_home_node, unsigned long, start, unsigned long, le
return -EINVAL;
if (end == start)
return 0;
- mmap_write_lock(mm);
+ if (mmap_write_lock_killable(mm))
+ return -EINTR;
prev = vma_prev(&vmi);
for_each_vma_range(vmi, vma, end) {
/*
@@ -1801,13 +1802,20 @@ SYSCALL_DEFINE4(set_mempolicy_home_node, unsigned long, start, unsigned long, le
err = -EOPNOTSUPP;
break;
}
+ /*
+ * Lock the VMA early to avoid extra work if fatal signal
+ * is pending.
+ */
+ if (vma_start_write_killable(vma)) {
+ err = -EINTR;
+ break;
+ }
new = mpol_dup(old);
if (IS_ERR(new)) {
err = PTR_ERR(new);
break;
}

- vma_start_write(vma);
new->home_node = home_node;
err = mbind_range(&vmi, vma, &prev, start, end, new);
mpol_put(new);
diff --git a/mm/mlock.c b/mm/mlock.c
index 8c227fefa2df..efbb9c783f25 100644
--- a/mm/mlock.c
+++ b/mm/mlock.c
@@ -419,8 +419,10 @@ static int mlock_pte_range(pmd_t *pmd, unsigned long addr,
*
* Called for mlock(), mlock2() and mlockall(), to set @vma VM_LOCKED;
* called for munlock() and munlockall(), to clear VM_LOCKED from @vma.
+ *
+ * Return: 0 on success, -EINTR if fatal signal is pending.
*/
-static void mlock_vma_pages_range(struct vm_area_struct *vma,
+static int mlock_vma_pages_range(struct vm_area_struct *vma,
unsigned long start, unsigned long end,
vma_flags_t *new_vma_flags)
{
@@ -442,7 +444,9 @@ static void mlock_vma_pages_range(struct vm_area_struct *vma,
*/
if (vma_flags_test(new_vma_flags, VMA_LOCKED_BIT))
vma_flags_set(new_vma_flags, VMA_IO_BIT);
- vma_start_write(vma);
+ if (vma_start_write_killable(vma))
+ return -EINTR;
+
vma_flags_reset_once(vma, new_vma_flags);

lru_add_drain();
@@ -453,6 +457,7 @@ static void mlock_vma_pages_range(struct vm_area_struct *vma,
vma_flags_clear(new_vma_flags, VMA_IO_BIT);
vma_flags_reset_once(vma, new_vma_flags);
}
+ return 0;
}

/*
@@ -506,11 +511,13 @@ static int mlock_fixup(struct vma_iterator *vmi, struct vm_area_struct *vma,
*/
if (vma_flags_test(&new_vma_flags, VMA_LOCKED_BIT) &&
vma_flags_test(&old_vma_flags, VMA_LOCKED_BIT)) {
+ ret = vma_start_write_killable(vma);
+ if (ret)
+ goto out;
/* No work to do, and mlocking twice would be wrong */
- vma_start_write(vma);
vma->flags = new_vma_flags;
} else {
- mlock_vma_pages_range(vma, start, end, &new_vma_flags);
+ ret = mlock_vma_pages_range(vma, start, end, &new_vma_flags);
}
out:
*prev = vma;
@@ -739,9 +746,18 @@ static int apply_mlockall_flags(int flags)

error = mlock_fixup(&vmi, vma, &prev, vma->vm_start, vma->vm_end,
newflags);
- /* Ignore errors, but prev needs fixing up. */
- if (error)
+ if (error) {
+ /*
+ * If we failed due to a pending fatal signal, return
+ * now. If we locked the vma before signal arrived, it
+ * will be unlocked when we drop mmap_write_lock.
+ */
+ if (fatal_signal_pending(current))
+ return -EINTR;
+
+ /* Ignore errors, but prev needs fixing up. */
prev = vma;
+ }
cond_resched();
}
out:
diff --git a/mm/mprotect.c b/mm/mprotect.c
index 110d47a36d4b..ae6ed882b600 100644
--- a/mm/mprotect.c
+++ b/mm/mprotect.c
@@ -768,7 +768,10 @@ mprotect_fixup(struct vma_iterator *vmi, struct mmu_gather *tlb,
* vm_flags and vm_page_prot are protected by the mmap_lock
* held in write mode.
*/
- vma_start_write(vma);
+ error = vma_start_write_killable(vma);
+ if (error)
+ goto fail;
+
vma_flags_reset_once(vma, &new_vma_flags);
if (vma_wants_manual_pte_write_upgrade(vma))
mm_cp_flags |= MM_CP_TRY_CHANGE_WRITABLE;
diff --git a/mm/mremap.c b/mm/mremap.c
index e9c8b1d05832..dec39ec314f9 100644
--- a/mm/mremap.c
+++ b/mm/mremap.c
@@ -1356,7 +1356,9 @@ static unsigned long move_vma(struct vma_remap_struct *vrm)
return -ENOMEM;

/* We don't want racing faults. */
- vma_start_write(vrm->vma);
+ err = vma_start_write_killable(vrm->vma);
+ if (err)
+ return err;

/* Perform copy step. */
err = copy_vma_and_data(vrm, &new_vma);
diff --git a/mm/vma.c b/mm/vma.c
index ba78ab1f397a..7930a4270eb9 100644
--- a/mm/vma.c
+++ b/mm/vma.c
@@ -524,6 +524,17 @@ __split_vma(struct vma_iterator *vmi, struct vm_area_struct *vma,
new->vm_pgoff += ((addr - vma->vm_start) >> PAGE_SHIFT);
}

+ /*
+ * Lock VMAs before cloning to avoid extra work if fatal signal
+ * is pending.
+ */
+ err = vma_start_write_killable(vma);
+ if (err)
+ goto out_free_vma;
+ err = vma_start_write_killable(new);
+ if (err)
+ goto out_free_vma;
+
err = -ENOMEM;
vma_iter_config(vmi, new->vm_start, new->vm_end);
if (vma_iter_prealloc(vmi, new))
@@ -543,9 +554,6 @@ __split_vma(struct vma_iterator *vmi, struct vm_area_struct *vma,
if (new->vm_ops && new->vm_ops->open)
new->vm_ops->open(new);

- vma_start_write(vma);
- vma_start_write(new);
-
init_vma_prep(&vp, vma);
vp.insert = new;
vma_prepare(&vp);
@@ -900,12 +908,16 @@ static __must_check struct vm_area_struct *vma_merge_existing_range(
}

/* No matter what happens, we will be adjusting middle. */
- vma_start_write(middle);
+ err = vma_start_write_killable(middle);
+ if (err)
+ goto abort;

if (merge_right) {
vma_flags_t next_sticky;

- vma_start_write(next);
+ err = vma_start_write_killable(next);
+ if (err)
+ goto abort;
vmg->target = next;
next_sticky = vma_flags_and_mask(&next->flags, VMA_STICKY_FLAGS);
vma_flags_set_mask(&sticky_flags, next_sticky);
@@ -914,7 +926,9 @@ static __must_check struct vm_area_struct *vma_merge_existing_range(
if (merge_left) {
vma_flags_t prev_sticky;

- vma_start_write(prev);
+ err = vma_start_write_killable(prev);
+ if (err)
+ goto abort;
vmg->target = prev;

prev_sticky = vma_flags_and_mask(&prev->flags, VMA_STICKY_FLAGS);
@@ -1170,10 +1184,12 @@ int vma_expand(struct vma_merge_struct *vmg)
vma_flags_t sticky_flags =
vma_flags_and_mask(&vmg->vma_flags, VMA_STICKY_FLAGS);
vma_flags_t target_sticky;
- int err = 0;
+ int err;

mmap_assert_write_locked(vmg->mm);
- vma_start_write(target);
+ err = vma_start_write_killable(target);
+ if (err)
+ return err;

target_sticky = vma_flags_and_mask(&target->flags, VMA_STICKY_FLAGS);

@@ -1201,6 +1217,13 @@ int vma_expand(struct vma_merge_struct *vmg)
* we don't need to account for vmg->give_up_on_mm here.
*/
if (remove_next) {
+ /*
+ * Lock the VMA early to avoid extra work if fatal signal
+ * is pending.
+ */
+ err = vma_start_write_killable(next);
+ if (err)
+ return err;
err = dup_anon_vma(target, next, &anon_dup);
if (err)
return err;
@@ -1214,7 +1237,6 @@ int vma_expand(struct vma_merge_struct *vmg)
if (remove_next) {
vma_flags_t next_sticky;

- vma_start_write(next);
vmg->__remove_next = true;

next_sticky = vma_flags_and_mask(&next->flags, VMA_STICKY_FLAGS);
@@ -1252,9 +1274,14 @@ int vma_shrink(struct vma_iterator *vmi, struct vm_area_struct *vma,
unsigned long start, unsigned long end, pgoff_t pgoff)
{
struct vma_prepare vp;
+ int err;

WARN_ON((vma->vm_start != start) && (vma->vm_end != end));

+ err = vma_start_write_killable(vma);
+ if (err)
+ return err;
+
if (vma->vm_start < start)
vma_iter_config(vmi, vma->vm_start, start);
else
@@ -1263,8 +1290,6 @@ int vma_shrink(struct vma_iterator *vmi, struct vm_area_struct *vma,
if (vma_iter_prealloc(vmi, NULL))
return -ENOMEM;

- vma_start_write(vma);
-
init_vma_prep(&vp, vma);
vma_prepare(&vp);
vma_adjust_trans_huge(vma, start, end, NULL);
@@ -1453,7 +1478,9 @@ static int vms_gather_munmap_vmas(struct vma_munmap_struct *vms,
if (error)
goto end_split_failed;
}
- vma_start_write(next);
+ error = vma_start_write_killable(next);
+ if (error)
+ goto munmap_gather_failed;
mas_set(mas_detach, vms->vma_count++);
error = mas_store_gfp(mas_detach, next, GFP_KERNEL);
if (error)
@@ -1848,12 +1875,16 @@ static void vma_link_file(struct vm_area_struct *vma, bool hold_rmap_lock)
static int vma_link(struct mm_struct *mm, struct vm_area_struct *vma)
{
VMA_ITERATOR(vmi, mm, 0);
+ int err;
+
+ err = vma_start_write_killable(vma);
+ if (err)
+ return err;

vma_iter_config(&vmi, vma->vm_start, vma->vm_end);
if (vma_iter_prealloc(&vmi, vma))
return -ENOMEM;

- vma_start_write(vma);
vma_iter_store_new(&vmi, vma);
vma_link_file(vma, /* hold_rmap_lock= */false);
mm->map_count++;
@@ -2239,9 +2270,8 @@ int mm_take_all_locks(struct mm_struct *mm)
* is reached.
*/
for_each_vma(vmi, vma) {
- if (signal_pending(current))
+ if (signal_pending(current) || vma_start_write_killable(vma))
goto out_unlock;
- vma_start_write(vma);
}

vma_iter_init(&vmi, mm, 0);
@@ -2540,8 +2570,8 @@ static int __mmap_new_vma(struct mmap_state *map, struct vm_area_struct **vmap,
struct mmap_action *action)
{
struct vma_iterator *vmi = map->vmi;
- int error = 0;
struct vm_area_struct *vma;
+ int error;

/*
* Determine the object being mapped and call the appropriate
@@ -2552,6 +2582,14 @@ static int __mmap_new_vma(struct mmap_state *map, struct vm_area_struct **vmap,
if (!vma)
return -ENOMEM;

+ /*
+ * Lock the VMA early to avoid extra work if fatal signal
+ * is pending.
+ */
+ error = vma_start_write_killable(vma);
+ if (error)
+ goto free_vma;
+
vma_iter_config(vmi, map->addr, map->end);
vma_set_range(vma, map->addr, map->end, map->pgoff);
vma->flags = map->vma_flags;
@@ -2582,8 +2620,6 @@ static int __mmap_new_vma(struct mmap_state *map, struct vm_area_struct **vmap,
WARN_ON_ONCE(!arch_validate_flags(map->vm_flags));
#endif

- /* Lock the VMA since it is modified after insertion into VMA tree */
- vma_start_write(vma);
vma_iter_store_new(vmi, vma);
map->mm->map_count++;
vma_link_file(vma, action->hide_from_rmap_until_complete);
@@ -2878,6 +2914,7 @@ int do_brk_flags(struct vma_iterator *vmi, struct vm_area_struct *vma,
unsigned long addr, unsigned long len, vma_flags_t vma_flags)
{
struct mm_struct *mm = current->mm;
+ int err;

/*
* Check against address space limits by the changed size
@@ -2910,24 +2947,33 @@ int do_brk_flags(struct vma_iterator *vmi, struct vm_area_struct *vma,

if (vma_merge_new_range(&vmg))
goto out;
- else if (vmg_nomem(&vmg))
+ if (vmg_nomem(&vmg)) {
+ err = -ENOMEM;
goto unacct_fail;
+ }
}

if (vma)
vma_iter_next_range(vmi);
/* create a vma struct for an anonymous mapping */
vma = vm_area_alloc(mm);
- if (!vma)
+ if (!vma) {
+ err = -ENOMEM;
goto unacct_fail;
+ }

vma_set_anonymous(vma);
vma_set_range(vma, addr, addr + len, addr >> PAGE_SHIFT);
vma->flags = vma_flags;
vma->vm_page_prot = vm_get_page_prot(vma_flags_to_legacy(vma_flags));
- vma_start_write(vma);
- if (vma_iter_store_gfp(vmi, vma, GFP_KERNEL))
+ if (vma_start_write_killable(vma)) {
+ err = -EINTR;
+ goto vma_lock_fail;
+ }
+ if (vma_iter_store_gfp(vmi, vma, GFP_KERNEL)) {
+ err = -ENOMEM;
goto mas_store_fail;
+ }

mm->map_count++;
validate_mm(mm);
@@ -2942,10 +2988,11 @@ int do_brk_flags(struct vma_iterator *vmi, struct vm_area_struct *vma,
return 0;

mas_store_fail:
+vma_lock_fail:
vm_area_free(vma);
unacct_fail:
vm_unacct_memory(len >> PAGE_SHIFT);
- return -ENOMEM;
+ return err;
}

/**
@@ -3112,8 +3159,8 @@ int expand_upwards(struct vm_area_struct *vma, unsigned long address)
struct mm_struct *mm = vma->vm_mm;
struct vm_area_struct *next;
unsigned long gap_addr;
- int error = 0;
VMA_ITERATOR(vmi, mm, vma->vm_start);
+ int error;

if (!vma_test(vma, VMA_GROWSUP_BIT))
return -EFAULT;
@@ -3149,12 +3196,14 @@ int expand_upwards(struct vm_area_struct *vma, unsigned long address)

/* We must make sure the anon_vma is allocated. */
if (unlikely(anon_vma_prepare(vma))) {
- vma_iter_free(&vmi);
- return -ENOMEM;
+ error = -ENOMEM;
+ goto vma_prep_fail;
}

/* Lock the VMA before expanding to prevent concurrent page faults */
- vma_start_write(vma);
+ error = vma_start_write_killable(vma);
+ if (error)
+ goto vma_lock_fail;
/* We update the anon VMA tree. */
anon_vma_lock_write(vma->anon_vma);

@@ -3183,6 +3232,8 @@ int expand_upwards(struct vm_area_struct *vma, unsigned long address)
}
}
anon_vma_unlock_write(vma->anon_vma);
+vma_lock_fail:
+vma_prep_fail:
vma_iter_free(&vmi);
validate_mm(mm);
return error;
@@ -3197,8 +3248,8 @@ int expand_downwards(struct vm_area_struct *vma, unsigned long address)
{
struct mm_struct *mm = vma->vm_mm;
struct vm_area_struct *prev;
- int error = 0;
VMA_ITERATOR(vmi, mm, vma->vm_start);
+ int error;

if (!vma_test(vma, VMA_GROWSDOWN_BIT))
return -EFAULT;
@@ -3228,12 +3279,14 @@ int expand_downwards(struct vm_area_struct *vma, unsigned long address)

/* We must make sure the anon_vma is allocated. */
if (unlikely(anon_vma_prepare(vma))) {
- vma_iter_free(&vmi);
- return -ENOMEM;
+ error = -ENOMEM;
+ goto vma_prep_fail;
}

/* Lock the VMA before expanding to prevent concurrent page faults */
- vma_start_write(vma);
+ error = vma_start_write_killable(vma);
+ if (error)
+ goto vma_lock_fail;
/* We update the anon VMA tree. */
anon_vma_lock_write(vma->anon_vma);

@@ -3263,6 +3316,8 @@ int expand_downwards(struct vm_area_struct *vma, unsigned long address)
}
}
anon_vma_unlock_write(vma->anon_vma);
+vma_lock_fail:
+vma_prep_fail:
vma_iter_free(&vmi);
validate_mm(mm);
return error;
diff --git a/mm/vma_exec.c b/mm/vma_exec.c
index 5cee8b7efa0f..8ddcc791d828 100644
--- a/mm/vma_exec.c
+++ b/mm/vma_exec.c
@@ -41,6 +41,7 @@ int relocate_vma_down(struct vm_area_struct *vma, unsigned long shift)
struct vm_area_struct *next;
struct mmu_gather tlb;
PAGETABLE_MOVE(pmc, vma, vma, old_start, new_start, length);
+ int err;

BUG_ON(new_start > new_end);

@@ -56,8 +57,9 @@ int relocate_vma_down(struct vm_area_struct *vma, unsigned long shift)
* cover the whole range: [new_start, old_end)
*/
vmg.target = vma;
- if (vma_expand(&vmg))
- return -ENOMEM;
+ err = vma_expand(&vmg);
+ if (err)
+ return err;

/*
* move the page tables downwards, on failure we rely on
--
2.53.0.1018.g2bb0e51243-goog