From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id DB2693BE620 for ; Mon, 31 Aug 2026 22:35:56 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1788215759; cv=none; b=Eu0jZltPsTP1zPeIqyOLBDIuU5xIq1pESlrx4G/7nhN2xBbiW4+rizjRHw/aa602dnMaEqssb9VxKCY8Tx6upxD7uT2dVrR/BTLsAudV0axIcCR/O8B98rWjyGTgW/MUp59yUGOTN6XW8WEEAFOBJhHLHTfsgH90UsIjYdNrVuI= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1788215759; c=relaxed/simple; bh=F5LMVv8egubwtHl7ILwllMN6DZTyd4j7i/bPW5BsG0Q=; h=Date:To:From:Subject:Message-Id; b=Ekh8HyCMzpDi75f1Wu3EbUsvmfpeBnOVIYz7W5Bm3HGHF4tL7tR5onRFUjnup7Oc9AG14WzBsvjT1oKusoW2IzdQrWXIbLZKw5RfAVqsxW/SP6faJDKVGwa9E6642P2IryL5AsFElO1mbV/B/0HYUD+vrnZD1FVDimGhFuhOPzQ= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux-foundation.org header.i=@linux-foundation.org header.b=tOtfj+IJ; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux-foundation.org header.i=@linux-foundation.org header.b="tOtfj+IJ" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 8D9AB1F000E9; Mon, 31 Aug 2026 22:35:56 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux-foundation.org; s=korg; t=1788215756; bh=tBhgV4x8qUIJFG4a7R0cWsgBnG2hCnNbPrY9L1sGxb0=; h=Date:To:From:Subject; b=tOtfj+IJuEQU3gmCZKugPjo0C6zJhwb/7mMhheS7Bj7cTdGnM1yNr7AJB60zhFfwU /UW9jbRdgwsjWFEfJvZ3qpQ5R1ErOL1ae/4AXsxt6OdshtWif5rocRBI/7CzFfZ/72 kTNzIyl4AZEa/nzO0fuLdzm2kQl/9l+F7pDJnQ8A= Date: Mon, 31 Aug 2026 15:35:56 -0700 To: mm-commits@vger.kernel.org,vbabka@kernel.org,tkjos@android.com,surenb@google.com,shakeel.butt@linux.dev,ljs@kernel.org,Liam.Howlett@oracle.com,gregkh@linuxfoundation.org,dsahern@kernel.org,davem@davemloft.net,cmllamas@google.com,christian@brauner.io,arve@android.com,aliceryhl@google.com,dave.hansen@linux.intel.com,akpm@linux-foundation.org From: Andrew Morton Subject: + binder-remove-mmap_lock-fallback.patch added to mm-new branch Message-Id: <20260831223556.8D9AB1F000E9@smtp.kernel.org> Precedence: bulk X-Mailing-List: mm-commits@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: The patch titled Subject: binder: remove mmap_lock fallback has been added to the -mm mm-new branch. Its filename is binder-remove-mmap_lock-fallback.patch This patch will shortly appear at https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/binder-remove-mmap_lock-fallback.patch This patch will later appear in the mm-new branch at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm Note, mm-new is a provisional staging ground for work-in-progress patches, and acceptance into mm-new is a notification for others take notice and to finish up reviews. Please do not hesitate to respond to review feedback and post updated versions to replace or incrementally fixup patches in mm-new. The mm-new branch of mm.git is not included in linux-next If a few days of testing in mm-new is successful, the patch will me moved into mm.git's mm-unstable branch, which is included in linux-next Before you just go and hit "reply", please: a) Consider who else should be cc'ed b) Prefer to cc a suitable mailing list as well c) Ideally: find the original patch on the mailing list and do a reply-to-all to that, adding suitable additional cc's *** Remember to use Documentation/process/submit-checklist.rst when testing your code *** The -mm tree is included into linux-next via various branches at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm and is updated there most days ------------------------------------------------------ From: Dave Hansen Subject: binder: remove mmap_lock fallback Date: Mon, 31 Aug 2026 13:30:55 -0700 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. Link: https://lore.kernel.org/20260831203056.838265-5-surenb@google.com Signed-off-by: Dave Hansen Signed-off-by: Suren Baghdasaryan Reviewed-by: Alice Ryhl Acked-by: Lorenzo Stoakes (ARM) Cc: Liam R. Howlett Cc: Vlastimil Babka Cc: Shakeel Butt Cc: Greg Kroah-Hartman Cc: Todd Kjos Cc: Christian Brauner Cc: Carlos Llamas Cc: Alice Ryhl Cc: David S. Miller Cc: David Ahern Cc: Arve Hjønnevåg Signed-off-by: Andrew Morton --- drivers/android/binder/page_range.rs | 19 ++-------------- drivers/android/binder_alloc.c | 17 ++++----------- rust/kernel/mm.rs | 28 +++++++++++++++++++++++++ 3 files changed, 36 insertions(+), 28 deletions(-) --- a/drivers/android/binder_alloc.c~binder-remove-mmap_lock-fallback +++ a/drivers/android/binder_alloc.c @@ -259,21 +259,14 @@ static int binder_page_insert(struct bin struct vm_area_struct *vma; int ret = -ESRCH; - /* attempt per-vma lock first */ - vma = lock_vma_under_rcu(mm, addr); - if (vma) { - if (binder_alloc_is_mapped(alloc)) - ret = vm_insert_page(vma, addr, page); - vma_end_read(vma); + vma = vma_start_read_unlocked(mm, addr); + if (!vma) return ret; - } - /* fall back to mmap_lock */ - mmap_read_lock(mm); - vma = vma_lookup(mm, addr); - if (vma && binder_alloc_is_mapped(alloc)) + if (binder_alloc_is_mapped(alloc)) ret = vm_insert_page(vma, addr, page); - mmap_read_unlock(mm); + + vma_end_read(vma); return ret; } --- a/drivers/android/binder/page_range.rs~binder-remove-mmap_lock-fallback +++ a/drivers/android/binder/page_range.rs @@ -439,22 +439,9 @@ impl ShrinkablePageRange { // workqueue. let mm = MmWithUser::into_mmput_async(self.mm.mmget_not_zero().ok_or(ESRCH)?); { - let vma_read; - let mmap_read; - let vma = if let Some(ret) = mm.lock_vma_under_rcu(vma_addr) { - vma_read = ret; - check_vma(&vma_read, self) - } else { - mmap_read = mm.mmap_read_lock(); - mmap_read - .vma_lookup(vma_addr) - .and_then(|vma| check_vma(vma, self)) - }; - - match vma { - Some(vma) => vma.vm_insert_page(user_page_addr, &new_page)?, - None => return Err(ESRCH), - } + let vma_read_guard = mm.vma_start_read_unlocked(vma_addr).ok_or(ESRCH)?; + let vma = check_vma(&vma_read_guard, self).ok_or(ESRCH)?; + vma.vm_insert_page(user_page_addr, &new_page)?; } let inner = self.lock.lock(); --- a/rust/kernel/mm.rs~binder-remove-mmap_lock-fallback +++ a/rust/kernel/mm.rs @@ -186,6 +186,34 @@ impl MmWithUser { }) } + /// 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_locked(). + /// Nothing prevents VMAs being unmapped/mapped before or after the VMA is + /// looked up, if a stronger guarantee is required, take an mmap_lock. + /// + /// Return: If a VMA exists which spans @address, return that VMA, read-locked. + /// If no VMA is mapped there or, very unlikely, a reference count overflow + /// 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 = unsafe { bindings::vma_start_read_unlocked(self.as_raw(), vma_addr) }; + if vma.is_null() { + return None; + } + // INVARIANT: We just acquired the VMA read lock. + 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 lock is held. + vma: unsafe { VmaRef::from_raw(vma) }, + _nts: NotThreadSafe, + }) + } + /// Lock the mmap read lock. #[inline] pub fn mmap_read_lock(&self) -> MmapReadGuard<'_> { _ Patches currently in -mm which might be from dave.hansen@linux.intel.com are mm-make-per-vma-locks-available-universally.patch binder-make-shrinker-rely-solely-on-per-vma-lock.patch mm-add-rcu-based-vma-lookup-helper-that-waits-for-writers.patch binder-remove-mmap_lock-fallback.patch tcp-remove-mmap_lock-fallback-path.patch