From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-pj1-f71.google.com (mail-pj1-f71.google.com [209.85.216.71]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id AEB403932D5 for ; Mon, 31 Aug 2026 20:31:12 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.216.71 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1788208276; cv=none; b=WE6sgiCcp/v8ediEgrKTHwYckMCddAwoN1ICTNPYtsExbptOjAobsfVy59ev/bxUD6mJ/gfjGbpiNO99bLrEe5mepoJI/aXAKOHdXoKLyRY+9lxpLpXtjwV3LOKeYTCE8erqhJizsciAjV23N0qv7GSa7YpkqQdnqr0rlwG98Vg= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1788208276; c=relaxed/simple; bh=E5omcHuGcH/5sMqY70uPWGBn/Pv7a09NS/jGJbvxUDA=; h=Date:In-Reply-To:Mime-Version:References:Message-ID:Subject:From: To:Cc:Content-Type; b=NVXPl1FmZqZa3R66TFjoQKzZYM3R28TwXaEBMcGr6hr0Wc69w4VVvD2rISZL6C8M9H1CUKjr3qxPD0xxblw4dM3pCZWny+oF2lXPUE/4/QPjfGp04AV+qwtoGXKDCSho8GeJhPZX1Td9+b6J1kyOh+qkTdOPEVbphVoatQqnZfM= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=google.com; spf=pass smtp.mailfrom=flex--surenb.bounces.google.com; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b=UwjO+kRP; arc=none smtp.client-ip=209.85.216.71 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=google.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=flex--surenb.bounces.google.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b="UwjO+kRP" Received: by mail-pj1-f71.google.com with SMTP id 98e67ed59e1d1-398e1fafe17so291932a91.0 for ; Mon, 31 Aug 2026 13:31:12 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20251104; t=1788208272; x=1788813072; darn=vger.kernel.org; h=content-transfer-encoding:content-type:cc:to:from:subject :message-id:references:mime-version:in-reply-to:date:from:to:cc :subject:date:message-id:reply-to:content-type; bh=fMb1BIWAt7k71K1WS7NJDkr5bMmZbsfs3e75iDz3R4U=; b=UwjO+kRPdRYCN7XOF0SKWzCdwZYzLGaLUA83mFXoGZnSam+2QZ+MsWDfjCBo1gkpAo SyQerbaqC0HXCD9H2GvE56Z4tfLD0Z5C9p655IDZYQbiM1U6dH/fr6+ARJ4lQTBCX4Ms aACs42ZrAFCCGFELTv5+8OaqVR22S3KigQyE4H1lpL2qIH0yiMZP0e1p1HuGKBh+NokL tsglwUqoIzkzkMW/fE2CoEKGcjfw7MqvEumtSU3naNJx1i5WCP5bbXSCgJLXFkqh7hDD OKrta5LeTC0s+YDVSpCmb2ycN/7dyWzBDblWgOwtNG19/CmaWP+ciTAJSkbwy78dwr+B P3KQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20251104; t=1788208272; x=1788813072; h=content-transfer-encoding:content-type:cc:to:from:subject :message-id:references:mime-version:in-reply-to:date :x-gm-message-state:from:to:cc:subject:date:message-id:reply-to :content-type; bh=fMb1BIWAt7k71K1WS7NJDkr5bMmZbsfs3e75iDz3R4U=; b=hJR6xEiuG4Ukn2+lfqHF7KWDo6M5zc1cVkmYBb4lEwtgWxPId/e0juCbLZoDAWILif OXZ3fT5aGRKz76xVpKSK4NWOINVWi/t8b+QsxuKaWl8rMMdHLwW/R8ImAsRJk2Z/s+nJ WBl5K5bNRvBXlNOVUVAyWBXjvoRwxkhdAFl72ivOcxMy37j7fB0Xkd41SeGwAKlw1Y0H ryG8s/WdBIeb/606VZLATxA6czoQBe8/ZhuBKrwxMUHWZHMwFhAHDAjoa6U5QmF6M9Kn bz2adJBciu5QZccvSR/UVsXG/qyaLaORxCPj5OzVcFA4Bfb6PUuddxiKym67s1Sigou4 cJNw== X-Forwarded-Encrypted: i=1; AKwUvBwphOx5cnEuJRVfqkfjs1vSbuMRSwv5pjgh36S0TyYTZXiW61zeTFmGYl+v+y1U31C97K7Jut8=@vger.kernel.org X-Gm-Message-State: AFuF++lw6+up3QukEtjtHt1BnKpRulMASyNxOkH+KTwocz6Nciw1nCZx 06zx5XqR3Ig5TBGexmLI0M8/eaZgaTzUs3EFuoGhTXhde3RU0rW6TXk7Nh94pOdRO/OhQeplu9V AFY1Q7A== X-Received: from dlak6.prod.google.com ([2002:a05:701b:2906:b0:141:5987:7f07]) (user=surenb job=prod-delivery.src-stubby-dispatcher) by 2002:a17:90b:3c8a:b0:38e:524:8797 with SMTP id 98e67ed59e1d1-396d10076e9mr43087877a91.13.1788208271612; Mon, 31 Aug 2026 13:31:11 -0700 (PDT) Date: Mon, 31 Aug 2026 13:30:55 -0700 In-Reply-To: <20260831203056.838265-1-surenb@google.com> Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 References: <20260831203056.838265-1-surenb@google.com> X-Mailer: git-send-email 2.55.0.966.g6673acef38-goog Message-ID: <20260831203056.838265-5-surenb@google.com> Subject: [PATCH v7 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@redhat.com, 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 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 Signed-off-by: Suren Baghdasaryan --- 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(-) diff --git a/drivers/android/binder/page_range.rs b/drivers/android/binder/= page_range.rs index 52ffbf3504e7..71febd3d5b07 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 fcb744088e77..d6eae0aa7085 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..58bc1793fdaf 100644 --- a/rust/kernel/mm.rs +++ b/rust/kernel/mm.rs @@ -186,6 +186,34 @@ 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; + } + // 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 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 2.55.0.966.g6673acef38-goog