[PATCH v6 2/6] mm: use vma_start_write_killable() in mm syscalls

Suren Baghdasaryan
2026-03-27T20:55:25Z

Replace vma_start_write() with vma_start_write_killable() in syscalls,
improving reaction time to the kill signal.

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>
---
mm/madvise.c | 13 ++++++++++---
mm/memory.c | 2 ++
mm/mempolicy.c | 11 +++++++++--
mm/mlock.c | 30 ++++++++++++++++++++++++------
mm/mprotect.c | 25 +++++++++++++++++--------
mm/mremap.c | 8 +++++---
mm/mseal.c | 24 +++++++++++++++++++-----
7 files changed, 86 insertions(+), 27 deletions(-)

diff --git a/mm/madvise.c b/mm/madvise.c
index 69708e953cf5..f2c7b0512cdf 100644
--- a/mm/madvise.c
+++ b/mm/madvise.c
@@ -172,10 +172,17 @@ static int madvise_update_vma(vm_flags_t new_flags,
if (IS_ERR(vma))
return PTR_ERR(vma);

- madv_behavior->vma = vma;
+ /*
+ * If a new vma was created during vma_modify_XXX, the resulting
+ * vma is already locked. Skip re-locking new vma in this case.
+ */
+ if (vma == madv_behavior->vma) {
+ if (vma_start_write_killable(vma))
+ return -EINTR;
+ } else {
+ madv_behavior->vma = vma;
+ }

- /* vm_flags is protected by the mmap_lock held in write mode. */
- vma_start_write(vma);
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 e44469f9cf65..9f99ec634831 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 fd08771e2057..c38a90487531 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 +1802,19 @@ 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.
+ */
+ err = vma_start_write_killable(vma);
+ if (err)
+ 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..2ed454db7cf7 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 +511,15 @@ 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; /* mm->locked_vm is fine as nr_pages == 0 */
/* 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);
+ if (ret)
+ mm->locked_vm -= nr_pages;
}
out:
*prev = vma;
@@ -739,9 +748,18 @@ 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..d6227877465f 100644
--- a/mm/mprotect.c
+++ b/mm/mprotect.c
@@ -700,6 +700,7 @@ mprotect_fixup(struct vma_iterator *vmi, struct mmu_gather *tlb,
const vma_flags_t old_vma_flags = READ_ONCE(vma->flags);
vma_flags_t new_vma_flags = legacy_to_vma_flags(newflags);
long nrpages = (end - start) >> PAGE_SHIFT;
+ struct vm_area_struct *new_vma;
unsigned int mm_cp_flags = 0;
unsigned long charged = 0;
int error;
@@ -756,19 +757,27 @@ mprotect_fixup(struct vma_iterator *vmi, struct mmu_gather *tlb,
vma_flags_clear(&new_vma_flags, VMA_ACCOUNT_BIT);
}

- vma = vma_modify_flags(vmi, *pprev, vma, start, end, &new_vma_flags);
- if (IS_ERR(vma)) {
- error = PTR_ERR(vma);
+ new_vma = vma_modify_flags(vmi, *pprev, vma, start, end,
+ &new_vma_flags);
+ if (IS_ERR(new_vma)) {
+ error = PTR_ERR(new_vma);
goto fail;
}

- *pprev = vma;
-
/*
- * vm_flags and vm_page_prot are protected by the mmap_lock
- * held in write mode.
+ * If a new vma was created during vma_modify_flags, the resulting
+ * vma is already locked. Skip re-locking new vma in this case.
*/
- vma_start_write(vma);
+ if (new_vma == vma) {
+ error = vma_start_write_killable(vma);
+ if (error)
+ goto fail;
+ } else {
+ vma = new_vma;
+ }
+
+ *pprev = vma;
+
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..0860102bddab 100644
--- a/mm/mremap.c
+++ b/mm/mremap.c
@@ -1348,6 +1348,11 @@ static unsigned long move_vma(struct vma_remap_struct *vrm)
if (err)
return err;

+ /* We don't want racing faults. */
+ err = vma_start_write_killable(vrm->vma);
+ if (err)
+ return err;
+
/*
* If accounted, determine the number of bytes the operation will
* charge.
@@ -1355,9 +1360,6 @@ static unsigned long move_vma(struct vma_remap_struct *vrm)
if (!vrm_calc_charge(vrm))
return -ENOMEM;

- /* We don't want racing faults. */
- vma_start_write(vrm->vma);
-
/* Perform copy step. */
err = copy_vma_and_data(vrm, &new_vma);
/*
diff --git a/mm/mseal.c b/mm/mseal.c
index 603df53ad267..1ea19fd3d384 100644
--- a/mm/mseal.c
+++ b/mm/mseal.c
@@ -70,14 +70,28 @@ static int mseal_apply(struct mm_struct *mm,

if (!vma_test(vma, VMA_SEALED_BIT)) {
vma_flags_t vma_flags = vma->flags;
+ struct vm_area_struct *new_vma;

vma_flags_set(&vma_flags, VMA_SEALED_BIT);

- vma = vma_modify_flags(&vmi, prev, vma, curr_start,
- curr_end, &vma_flags);
- if (IS_ERR(vma))
- return PTR_ERR(vma);
- vma_start_write(vma);
+ new_vma = vma_modify_flags(&vmi, prev, vma, curr_start,
+ curr_end, &vma_flags);
+ if (IS_ERR(new_vma))
+ return PTR_ERR(new_vma);
+
+ /*
+ * If a new vma was created during vma_modify_flags,
+ * the resulting vma is already locked.
+ * Skip re-locking new vma in this case.
+ */
+ if (new_vma == vma) {
+ int err = vma_start_write_killable(vma);
+ if (err)
+ return err;
+ } else {
+ vma = new_vma;
+ }
+
vma_set_flags(vma, VMA_SEALED_BIT);
}

--
2.53.0.1018.g2bb0e51243-goog