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Miller" , Greg Kroah-Hartman , "Liam R. Howlett" , linux-mm@kvack.org, Lorenzo Stoakes , netdev@vger.kernel.org, Shakeel Butt , Suren Baghdasaryan , Todd Kjos , Vlastimil Babka Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: quoted-printable On Wed, Jun 10, 2026 at 04:04:17PM -0700, Dave Hansen wrote: >=20 > From: Dave Hansen >=20 > Previously, the per-VMA locking could fail in the face of writers > which necessitate a fallback to mmap_lock. The new > vma_start_read_unlocked() will wait for writers instead of failing. >=20 > Use the new helper. Wait for writers. Remove the fallback to mmap_lock. >=20 > Signed-off-by: Dave Hansen > Acked-by: Lorenzo Stoakes > Reviewed-by: Suren Baghdasaryan > Cc: Andrew Morton > Cc: "Liam R. Howlett" > Cc: Vlastimil Babka > Cc: Shakeel Butt > Cc: linux-mm@kvack.org > Cc: Greg Kroah-Hartman > Cc: Arve Hj=C3=B8nnev=C3=A5g > Cc: Todd Kjos > Cc: Christian Brauner > Cc: Carlos Llamas > Cc: Alice Ryhl > Cc: "David S. Miller" > Cc: David Ahern > Cc: netdev@vger.kernel.org >=20 > --- >=20 > b/drivers/android/binder_alloc.c | 17 +++++------------ > 1 file changed, 5 insertions(+), 12 deletions(-) >=20 > diff -puN drivers/android/binder_alloc.c~binder-vma-waiter drivers/androi= d/binder_alloc.c > --- a/drivers/android/binder_alloc.c~binder-vma-waiter 2026-06-10 15:57:5= 6.419452721 -0700 > +++ b/drivers/android/binder_alloc.c 2026-06-10 15:57:56.423452863 -0700 > @@ -259,21 +259,14 @@ static int binder_page_insert(struct bin > struct vm_area_struct *vma; > int ret =3D -ESRCH; > =20 > - /* attempt per-vma lock first */ > - vma =3D lock_vma_under_rcu(mm, addr); > - if (vma) { > - if (binder_alloc_is_mapped(alloc)) > - ret =3D vm_insert_page(vma, addr, page); > - vma_end_read(vma); > + vma =3D vma_start_read_unlocked(mm, addr); > + if (!vma) > return ret; > - } > =20 > - /* fall back to mmap_lock */ > - mmap_read_lock(mm); > - vma =3D vma_lookup(mm, addr); > - if (vma && binder_alloc_is_mapped(alloc)) > + if (binder_alloc_is_mapped(alloc)) > ret =3D vm_insert_page(vma, addr, page); > - mmap_read_unlock(mm); > + > + vma_end_read(vma); > =20 > return ret; > } > _ It would be nice if we could update Rust Binder as well. diff --git a/drivers/android/binder/page_range.rs b/drivers/android/binder/= page_range.rs index e54a90e62402..8d56b991744f 100644 --- a/drivers/android/binder/page_range.rs +++ b/drivers/android/binder/page_range.rs @@ -439,22 +439,9 @@ unsafe fn use_page_slow(&self, i: usize) -> Result<()>= { // workqueue. let mm =3D MmWithUser::into_mmput_async(self.mm.mmget_not_zero().o= k_or(ESRCH)?); { - let vma_read; - let mmap_read; - let vma =3D if let Some(ret) =3D mm.lock_vma_under_rcu(vma_add= r) { - vma_read =3D ret; - check_vma(&vma_read, self) - } else { - mmap_read =3D mm.mmap_read_lock(); - mmap_read - .vma_lookup(vma_addr) - .and_then(|vma| check_vma(vma, self)) - }; - - match vma { - Some(vma) =3D> vma.vm_insert_page(user_page_addr, &new_pag= e)?, - None =3D> return Err(ESRCH), - } + let vma_read_guard =3D mm.vma_start_read_unlocked(vma_addr).ok= _or(ESRCH)?; + let vma =3D check_vma(&vma_read_guard, self).ok_or(ESRCH)?; + vma.vm_insert_page(user_page_addr, &new_page)?; } =20 let inner =3D self.lock.lock(); diff --git a/rust/kernel/mm.rs b/rust/kernel/mm.rs index 16f617d11479..2973718af48e 100644 --- a/rust/kernel/mm.rs +++ b/rust/kernel/mm.rs @@ -188,6 +188,24 @@ pub fn lock_vma_under_rcu(&self, vma_addr: usize) -> O= ption> { }) } =20 + /// Find the VMA covering 'address' and lock it for reading. Waits for= writers to finish if the + /// VMA is being modified. + #[inline] + pub fn vma_start_read_unlocked(&self, vma_addr: usize) -> Option> { + // SAFETY: We may invoke `vma_start_read_unlocked` because we know= this `mm` has non-zero + // `mm_users`. + let vma =3D unsafe { bindings::vma_start_read_unlocked(self.as_raw= (), vma_addr) }; + if vma.is_null() { + return None; + } + Some(VmaReadGuard { + // SAFETY: If `vma_start_read_unlocked` returns a non-null ptr= , then it points at a + // valid vma. The vma is stable for as long as the vma read lo= ck is held. + vma: unsafe { VmaRef::from_raw(vma) }, + _nts: NotThreadSafe, + }) + } + /// Lock the mmap read lock. #[inline] pub fn mmap_read_lock(&self) -> MmapReadGuard<'_> { Alice