From nobody Thu Dec 18 00:28:46 2025 Received: from mail-pf1-f202.google.com (mail-pf1-f202.google.com [209.85.210.202]) (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 2CDE8206F35 for ; Mon, 16 Dec 2024 19:24:26 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.210.202 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1734377067; cv=none; b=My1YLWT8p2Euf35atBExKQhnyN2i1rtJVM8hvgnPc7XzPrkddJnT3/kBwMNtWK/6U5RoyMeA7LIaNkmhcSmFwVofGKlxKGmgQiEC3Us7dKEvtB/VfqHu8uq/D9QLyJFFe5W/7MIMdvu5T1d8YSUtT4L96U49hYuyN4oLQfv/7ac= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1734377067; c=relaxed/simple; bh=ZuhVNkkcxX9XPqzBdhxdevat7/UtnVBp6WiY/j9FpKE=; h=Date:In-Reply-To:Mime-Version:References:Message-ID:Subject:From: To:Cc:Content-Type; b=sDL/bFtm6GXVojriwcxoO+7UspHIIc+LMcysiHIzqHvSXB0UhBqXr4jhPhXBfQJRaU90IYpWzzmjh1NYyeh/V8YT25NfiPLYz21/ajlT76OdF2XrTdodd9t8FKdFRr3w6Cdz+BcuY7kiM4eCt9/lk1Fs03R8L+ro5jw0DkZAG/s= 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=CPEHp+Gl; arc=none smtp.client-ip=209.85.210.202 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="CPEHp+Gl" Received: by mail-pf1-f202.google.com with SMTP id d2e1a72fcca58-725eb1e9139so6564702b3a.1 for ; Mon, 16 Dec 2024 11:24:26 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20230601; t=1734377065; x=1734981865; darn=vger.kernel.org; h=cc:to:from:subject:message-id:references:mime-version:in-reply-to :date:from:to:cc:subject:date:message-id:reply-to; bh=NdPtaL44NpTjP9eS1K5KVvptksJqAFYIrPxgR/8blQY=; b=CPEHp+Glaf1mdGuw1Hmj22UTVdsJELco1PEoU2WWGYqk2G/Ypzdzva1D1/EBpwwZhP mR8tKWw3z5rlp4852r7WFYfa1qK648yfInvuAAJ8vkMg2blFiKSJSMsE5ClL1jV+2sv1 4muu+HI/eUCdxuRcG/+V38OdcrMF7FEcfP8g+ZZuD+4iX3a1NVXSoW0oJIzax+NtdVJf 6Bn5VbwzB4PD2HvYXubSYOGQ+bGlSRbS/Ctwjzn8dFQnkHgYdOiP38yImqueWjKoDV1a ucmZAMkkcV/LJxupJinzBLaGgpj7d1OIonstHtYov5a4j83tH+zsdj5DtTLD78DEZX4d GM4Q== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1734377065; x=1734981865; h=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; bh=NdPtaL44NpTjP9eS1K5KVvptksJqAFYIrPxgR/8blQY=; b=Ty3z9ApleyYq/d2GO9F9w798Y0clrn3HnyoB8Dyx/c7hiUvIOFYUPQAXQ+BSOTyS8G dYjr2MqX2JGiVCaTgxX2L0OK2L/eqQntY/1V6JPTiUAzO2LHJQqhNgQpXj0CKJXIKM7h NlyWzQoXDCa+b6VzPI65Vd2jkfweBi69QmcQM3bJrtfCDG+nBol2D12koSLuyUj35WRS oa7WhiBE242Iz7kWpbcDYIsQqsfDOnkn046A4FTfKbrzHMjcaUc3Rd3qZ2BbGgWF150w atUsEhzgTaB5GMuuYSgqNFGMUKzXWX+v1hxtq/4v52IkbSvylkIl58H7asZh1xTxGPuX /U6Q== X-Forwarded-Encrypted: i=1; AJvYcCU4ecRht8/xeBsjsqE4oN5GwT/Z6P8NJegrkn9X1OTZGwrHhx0zwaznwqQzwmyh/xP1dosIY1gjN9MILK4=@vger.kernel.org X-Gm-Message-State: AOJu0YyvpWr0wG6LxRnCbzoy3nYnVvIxE16T0Oe9Z7m2Rt8nXT+EHXdW m5ti3ccQ8tKmE2SmRGknZXlYrM1k4a/OwckCKT8K8AQEav9bjRn8n6db+cTrpPzX5kK77g5WRyo TgQ== X-Google-Smtp-Source: AGHT+IGebkhkuPAK7qZirmEWQkyXcqUHZOWu2H7W9h1+nHtKbr+4oTQtJb1gp01e4aHBI2bniuiuItfkaYg= X-Received: from pfbbs2.prod.google.com ([2002:a05:6a00:4442:b0:725:e2fd:dcf9]) (user=surenb job=prod-delivery.src-stubby-dispatcher) by 2002:a05:6a00:4305:b0:725:973f:9d53 with SMTP id d2e1a72fcca58-7290c19ec16mr16656092b3a.15.1734377065528; Mon, 16 Dec 2024 11:24:25 -0800 (PST) Date: Mon, 16 Dec 2024 11:24:04 -0800 In-Reply-To: <20241216192419.2970941-1-surenb@google.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 References: <20241216192419.2970941-1-surenb@google.com> X-Mailer: git-send-email 2.47.1.613.gc27f4b7a9f-goog Message-ID: <20241216192419.2970941-2-surenb@google.com> Subject: [PATCH v6 01/16] mm: introduce vma_start_read_locked{_nested} helpers From: Suren Baghdasaryan To: akpm@linux-foundation.org Cc: peterz@infradead.org, willy@infradead.org, liam.howlett@oracle.com, lorenzo.stoakes@oracle.com, mhocko@suse.com, vbabka@suse.cz, hannes@cmpxchg.org, mjguzik@gmail.com, oliver.sang@intel.com, mgorman@techsingularity.net, david@redhat.com, peterx@redhat.com, oleg@redhat.com, dave@stgolabs.net, paulmck@kernel.org, brauner@kernel.org, dhowells@redhat.com, hdanton@sina.com, hughd@google.com, lokeshgidra@google.com, minchan@google.com, jannh@google.com, shakeel.butt@linux.dev, souravpanda@google.com, pasha.tatashin@soleen.com, klarasmodin@gmail.com, corbet@lwn.net, linux-doc@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, kernel-team@android.com, surenb@google.com Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" Introduce helper functions which can be used to read-lock a VMA when holding mmap_lock for read. Replace direct accesses to vma->vm_lock with these new helpers. Signed-off-by: Suren Baghdasaryan Reviewed-by: Lorenzo Stoakes Reviewed-by: Davidlohr Bueso Reviewed-by: Shakeel Butt Reviewed-by: Vlastimil Babka --- include/linux/mm.h | 24 ++++++++++++++++++++++++ mm/userfaultfd.c | 22 +++++----------------- 2 files changed, 29 insertions(+), 17 deletions(-) diff --git a/include/linux/mm.h b/include/linux/mm.h index 1352147a2648..3815a43ba504 100644 --- a/include/linux/mm.h +++ b/include/linux/mm.h @@ -735,6 +735,30 @@ static inline bool vma_start_read(struct vm_area_struc= t *vma) return true; } =20 +/* + * Use only while holding mmap read lock which guarantees that locking wil= l not + * fail (nobody can concurrently write-lock the vma). vma_start_read() sho= uld + * not be used in such cases because it might fail due to mm_lock_seq over= flow. + * This functionality is used to obtain vma read lock and drop the mmap re= ad lock. + */ +static inline void vma_start_read_locked_nested(struct vm_area_struct *vma= , int subclass) +{ + mmap_assert_locked(vma->vm_mm); + down_read_nested(&vma->vm_lock->lock, subclass); +} + +/* + * Use only while holding mmap read lock which guarantees that locking wil= l not + * fail (nobody can concurrently write-lock the vma). vma_start_read() sho= uld + * not be used in such cases because it might fail due to mm_lock_seq over= flow. + * This functionality is used to obtain vma read lock and drop the mmap re= ad lock. + */ +static inline void vma_start_read_locked(struct vm_area_struct *vma) +{ + mmap_assert_locked(vma->vm_mm); + down_read(&vma->vm_lock->lock); +} + static inline void vma_end_read(struct vm_area_struct *vma) { rcu_read_lock(); /* keeps vma alive till the end of up_read */ diff --git a/mm/userfaultfd.c b/mm/userfaultfd.c index 8e16dc290ddf..bc9a66ec6a6e 100644 --- a/mm/userfaultfd.c +++ b/mm/userfaultfd.c @@ -84,16 +84,8 @@ static struct vm_area_struct *uffd_lock_vma(struct mm_st= ruct *mm, =20 mmap_read_lock(mm); vma =3D find_vma_and_prepare_anon(mm, address); - if (!IS_ERR(vma)) { - /* - * We cannot use vma_start_read() as it may fail due to - * false locked (see comment in vma_start_read()). We - * can avoid that by directly locking vm_lock under - * mmap_lock, which guarantees that nobody can lock the - * vma for write (vma_start_write()) under us. - */ - down_read(&vma->vm_lock->lock); - } + if (!IS_ERR(vma)) + vma_start_read_locked(vma); =20 mmap_read_unlock(mm); return vma; @@ -1491,14 +1483,10 @@ static int uffd_move_lock(struct mm_struct *mm, mmap_read_lock(mm); err =3D find_vmas_mm_locked(mm, dst_start, src_start, dst_vmap, src_vmap); if (!err) { - /* - * See comment in uffd_lock_vma() as to why not using - * vma_start_read() here. - */ - down_read(&(*dst_vmap)->vm_lock->lock); + vma_start_read_locked(*dst_vmap); if (*dst_vmap !=3D *src_vmap) - down_read_nested(&(*src_vmap)->vm_lock->lock, - SINGLE_DEPTH_NESTING); + vma_start_read_locked_nested(*src_vmap, + SINGLE_DEPTH_NESTING); } mmap_read_unlock(mm); return err; --=20 2.47.1.613.gc27f4b7a9f-goog