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

[Suren Baghdasaryan <surenb@google.com>]

On Mon, Mar 23, 2026 at 10:49 AM Lorenzo Stoakes (Oracle)
<ljs@kernel.org> wrote:
>
> On Sat, Mar 21, 2026 at 10:43:06PM -0700, Suren Baghdasaryan wrote:
> > 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
>
> This really really needs splitting up into separate patches for the various
> bits you change, I know it might seem pedantic, but it's much harder to
> review this as one big patch, and hurts bisectability/specificity of fixes
> etc.
>
> Come, embrace the stats :)
>
> You are welcome to apply a 'Reviewed-by: Lorenzo Stoakes (Oracle)
> <ljs@kernel.org>' tag to all of the split-out patches where I have said
> LGTM throughout!

Thanks!
How would you suggest splitting the patch? I'm outlining one possible
division below. Let me know if you want to slice it differently:

>
> > ---
> >  arch/powerpc/kvm/book3s_hv_uvmem.c |   5 +-

The above one can obviously be split as it's powerpc specific.

> >  mm/khugepaged.c                    |   5 +-
> >  mm/madvise.c                       |   4 +-
> >  mm/memory.c                        |   2 +

The changes in the above files are almost one-liners with the last one
being just a comment change. Should each one go into a separate patch?

> >  mm/mempolicy.c                     |  12 ++-

I guess mempolicy one can be a separate patch.

> >  mm/mlock.c                         |  28 +++++--
> >  mm/mprotect.c                      |   5 +-
> >  mm/mremap.c                        |   4 +-

Maybe the above 3 can go together?

> >  mm/vma.c                           | 117 +++++++++++++++++++++--------
> >  mm/vma_exec.c                      |   6 +-

The above two files I think can go together and this is the most sizable one.


> >  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;
> > +             }
>
> LGTM
>
> >               /* 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;
> > +     }
>
> LGTM
>
> >       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;
> > +
>
> LGTM
>
> >       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.
>
> Nice.
>
> >   *
> >   * 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;
> > +             }
>
> LGTM, one nitty thing - wonder if we shouldn't pass through the error from
> vma_start_write_killable()? OTOH, it's not really a big deal. I don't
> foresee us ever returning anything but -EINTR or 0 :)

Ack. I'll change err to record vma_start_write_killable() return value instead.

>
> >               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;
> > +
>
> LGTM
>
> >       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;
>
> LGTM
>
> >               /* 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);
>
> LGTM
>
> >       }
> >  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;
>
> LGTM, and thanks for careful explanation, hopefully addresses Matthew's
> concerns ([0]).

That was my goal :)

>
> [0]:https://lore.kernel.org/all/aaiBX5Mm36Kg0wq1@casper.infradead.org/
>
> > +
> > +                     /* 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;
> > +
>
> LGTM
>
> >       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;
>
> Yeah this is subtle, I saw sashiko flagged it, so I checked and this isn't
> being accounted properly.
>
> vrm_calc_charge() charges via
> security_vm_enough_memory_mm()->__vm_enough_memory()->vm_acct_memory()
>
> And we only uncharge via vrm_uncharge()->vm_unacct_memory()
>
> The other error function there is:
>
>         err = copy_vma_and_data(vrm, &new_vma);
>         ...
>         if (err && !new_vma)
>                 return err;
>
> And in copy_vma_and_data():
>
>         if (!new_vma) {
>                 vrm_uncharge(vrm);
>                 *new_vma_ptr = NULL;
>                 return -ENOMEM;
>         }
>
> So that's already taken care of for us.
>
> It's stuff like this that is why it's important to separate this patch into
> separate patches :)
>
> We also do some weird and wonderful stuff with error handling where we try
> to back out the remapped page tables, having swapped the new and old VMAs
> around so the unmapping of the source VMA is done on the destination (yeah
> it's horrible).
>
> So this is all very subtle really.
>
> Honestly you might just be better off moving the vma_start_write_killable()
> above vrm_calc_charge()?

Yes I'll try that...

>
> If not, you'd just need to replace this with:
>
>         err = vma_start_write_killable(vrm->vma);
>         if (err) {
>                 vrm_uncharge(vrm);
>                 return err;
>         }

and if it doesn't work will do the above.

>
> >
> >       /* 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;
> > +
>
> LGTM
>
> >       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);
> > -
>
> LGTM
>
> >       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;
>
> I mean looking at this again the vmg_oom() etc. stuff is horrible and I
> definitely need to rework it. Sorry about that!
>
> I think we need to update vma_modify():
>
>         /* First, try to merge. */
>         merged = vma_merge_existing_range(vmg);
>         if (merged)
>                 return merged;
>         if (vmg_nomem(vmg))
>                 return ERR_PTR(-ENOMEM);
> +       if (fatal_signal_pending(current))

We need to be careful here. I think there are cases when vma is
modified from a context of a different process, for example in
process_madvise(). fatal_signal_pending(current) would yield incorrect
result because vma->vm_mm is not the same as current->mm.

> +               return -EINTR;
>
> So we can just get out early in this case. I _think_ that should be safe?
> :)
>
> If not, we could hack things here by doing:
>
>         if (err) {
>                 /* Ensure error propagated. */
>                 vmg->give_up_on_oom = false;
>                 goto abort;
>         }

I think that would be safer.

>
> And I can just go fix this all up afterwards.
>
> I still don't want a vmg_intr() or anything though, I will rework this into
> something saner!
>
> Anyway apologies, it's entirely my fault that this is a bit of a mess :)

No worries. We all make mistakes that become obvious only later.
Hindsight is always 20/20.

>
> >
> >       if (merge_right) {
> >               vma_flags_t next_sticky;
> >
> > -             vma_start_write(next);
> > +             err = vma_start_write_killable(next);
> > +             if (err)
> > +                     goto abort;
>
> Obv not withstanding above LGTM
>
> >               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;
>
> Ditto
>
> >               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;
>
> Yeah dup_anon stuff will not be done yet so this LGTM
>
> >
> >       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;
>
> Same here, so LGTM
>
> >               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);
>
> LGTM
>
> >               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);
> > -
>
> We will hold the VMA write lock even though we return -ENOMEM, but I guess
> not a big deal as we will drop the mmap write lock on error at the earliest
> opportunity anyway.
>
> So LGTM
>
> >       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;
>
> LGTM
>
> >               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;
>
> LGTM
>
> >
> >       vma_iter_config(&vmi, vma->vm_start, vma->vm_end);
> >       if (vma_iter_prealloc(&vmi, vma))
> >               return -ENOMEM;
> >
> > -     vma_start_write(vma);
>
> LGTM
>
> >       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))
>
> Hmm, surely signal_pending() should catch it :) but I suppose there could
> be a (very very tight) timing issue here, but case to be made for not
> converting this?

I want to convert all possible vma_start_write() cases in the hopes
that over time I might be able to deprecate vma_start_write()
completely. It's not possible right now (see the changelog) but with
some effort we might get there eventually.

>
> OTOH it doesn't really make much difference I guess.
>
> >                       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;
> > +
>
> LGTM
>
> >       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);
>
> LGTM
>
> >       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;
>
> LGTM
>
> >
> >       /*
> >        * 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;
> > +             }
>
> LGTM
>
> >       }
> >
> >       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;
> > +     }
>
> LGTM
>
> >
> >       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;
> > +     }
>
> LGTM
>
> > +     if (vma_iter_store_gfp(vmi, vma, GFP_KERNEL)) {
> > +             err = -ENOMEM;
> >               goto mas_store_fail;
> > +     }
>
> LGTM
>
> >
> >       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;
>
> LGTM
>
> >  }
> >
> >  /**
> > @@ -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;
>
> LGTM
>
> >
> >       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;
>
> Hm, but before we weren't calling validate_mm() here, and now we will be, I
> suspect we probably don't want to do that on error. Will comment on it
> below in that bit of the code.
>
> Otherwise, LGTM.
>
> >       }
> >
> >       /* 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;
>
> LGTM
>
> >       /* 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:
>
> LGTM
>
> >       vma_iter_free(&vmi);
> >       validate_mm(mm);
>
> Maybe this should be put before the labels?
>
> Then again, I guess there's no harm in it. But I'm not sure taking a long
> time to check the entire maple tree when CONFIG_DEBUG_VM_MAPLE_TREE is
> enabled is a good idea with a fatal signal pending?

That makes sense. Validating a tree when we know something went wrong
is probably meaningless. I'll move it before the jump labels.

>
> >       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;
>
> LGTM
>
> >
> >       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:
>
> Obv same comments for expand_upwards() apply here also.
>
> >       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;
>
> LGTM

Thanks for the detailed review!

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