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AHgh+RoJE83P5GkECgQ86wMuY1kNqLXQJmdR2GhUWwcSltBPp/pZRbokCO0R4Emd1d7MUe96+xN2JJ4gfs/O0fM=@vger.kernel.org X-Gm-Message-State: AOJu0Yy9xYK7aAguuU3Q3F2wrtO2CIRf2O9z41z6+Ggf+fDErUBVdxbQ zx2cMnvyOxCEBlp+hdou3ktrNxaQtz1RUuGlXX5FEVzu/rbL28dbFM6jjPeHMcR2r9nhx+p0Pxf 1XS4ryA== X-Received: from dybqh4.prod.google.com ([2002:a05:7301:6244:b0:30c:83f3:7370]) (user=surenb job=prod-delivery.src-stubby-dispatcher) by 2002:a05:6a21:6daa:b0:3c4:3672:ba6 with SMTP id adf61e73a8af0-3cbadc15329mr4732449637.22.1786046759808; Thu, 06 Aug 2026 13:05:59 -0700 (PDT) Date: Thu, 6 Aug 2026 13:05:47 -0700 In-Reply-To: <20260806200548.3124802-1-surenb@google.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 References: <20260806200548.3124802-1-surenb@google.com> X-Mailer: git-send-email 2.55.0.654.g21b8a5bc05-goog Message-ID: <20260806200548.3124802-5-surenb@google.com> Subject: [PATCH v4 4/5] binder: Remove mmap_lock fallback From: Suren Baghdasaryan To: akpm@linux-foundation.org Cc: dave.hansen@linux.intel.com, Liam.Howlett@oracle.com, ljs@kernel.org, david@kernel.org, willy@infradead.org, shakeel.butt@linux.dev, vbabka@kernel.org, jannh@google.com, aliceryhl@google.com, arve@android.com, cmllamas@google.com, christian@brauner.io, tkjos@android.com, dsahern@kernel.org, davem@davemloft.net, gregkh@linuxfoundation.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, netdev@vger.kernel.org, surenb@google.com Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable From: Dave Hansen 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. Use the new helper. Wait for writers. Remove the fallback to mmap_lock. Signed-off-by: Dave Hansen Signed-off-by: Suren Baghdasaryan Reviewed-by: Alice Ryhl Acked-by: Lorenzo Stoakes (ARM) 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 --- drivers/android/binder/page_range.rs | 19 +++---------------- drivers/android/binder_alloc.c | 17 +++++------------ rust/kernel/mm.rs | 27 +++++++++++++++++++++++++++ 3 files changed, 35 insertions(+), 28 deletions(-) diff --git a/drivers/android/binder/page_range.rs b/drivers/android/binder/= page_range.rs index e82a5523804f..f7ad88a0d806 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/drivers/android/binder_alloc.c b/drivers/android/binder_alloc.= c index c13a588c37de..efa23f6b8360 100644 --- a/drivers/android/binder_alloc.c +++ b/drivers/android/binder_alloc.c @@ -259,21 +259,14 @@ static int binder_page_insert(struct binder_alloc *al= loc, 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; } diff --git a/rust/kernel/mm.rs b/rust/kernel/mm.rs index f4fa54616085..11466fb304df 100644 --- a/rust/kernel/mm.rs +++ b/rust/kernel/mm.rs @@ -186,6 +186,33 @@ pub fn lock_vma_under_rcu(&self, vma_addr: usize) -> O= ption> { }) } =20 + /// Find the VMA covering 'address' and read-lock it. + /// + /// The fast path does not take mmap_lock. Waits for writers to finish= if the + /// VMA is being modified by taking mmap_lock. + /// Use when mmap_lock is not held, otherwise use vma_start_read_locke= d(). + /// Nothing prevents VMAs being unmapped/mapped before or after the VM= A is + /// looked up, if a stronger guarantee is required, take an mmap_lock. + /// + /// Return: If a VMA exists which spans @address, return that VMA, rea= d-locked. + /// If no VMA is mapped there or, very unlikely, a reference count ove= rflow + /// occurred, return NULL. + #[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<'_> { --=20 2.55.0.654.g21b8a5bc05-goog