From nobody Wed Dec 17 12:11:17 2025 Received: from mail-pj1-f73.google.com (mail-pj1-f73.google.com [209.85.216.73]) (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 BE5853B192 for ; Thu, 9 Jan 2025 02:30:31 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.216.73 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1736389833; cv=none; b=V0f2AwoaILJyV40h3zgPFWJEYucECVX+tR/1wlp4SQNQZYtGbmNm/4yIoGnZ2gdRG/8E8oobaFmVdSkFMoL3vOv7IoTbWIunl67RnBzpy8/3IuhDVGj0ZM+T0CBqECAUY4syQXA6eI7X7gPBBE2hM3ExwXB8btjcsdJkxSpO6ww= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1736389833; c=relaxed/simple; bh=hJuoXOD+Hgs/Q4Tge4AjDWFB01AUx9ksvDVIv+G6+4M=; h=Date:In-Reply-To:Mime-Version:References:Message-ID:Subject:From: To:Cc:Content-Type; b=bhJdRJGBiJ/vqY46tBZsBvLQSLrp8jPGRkBk0KUY6phu8QajGLrUcc7kmrQIOCnXf0AxraxCckqDL5960mtZ3hATsntIGKNOTnliSzUgzr1qEPq6NlP3oI7X7roHbWPphByu+DssXyWGiBGVfUgnYG5DyCKVdJq1dEr/2l1Teu8= 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=VKbwklV9; arc=none smtp.client-ip=209.85.216.73 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="VKbwklV9" Received: by mail-pj1-f73.google.com with SMTP id 98e67ed59e1d1-2ef775ec883so760081a91.1 for ; Wed, 08 Jan 2025 18:30:31 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20230601; t=1736389831; x=1736994631; 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=L2pdotIvyMZQNnGmgTfsGf0xKAYx/XKZavKJSJfbFgY=; b=VKbwklV917NYg2LHHTu8NWDzLIReJHfpSYINoU65sQLGNnHI3X+5EhKAzJhyL/+/vv K3TIA2wzk4o+5VhXKAHuYfy0SDhNuyLE0JdGG4B15utO4JqAri+0CQ4gF6cGEY3WW7GN ceEQOh/LPDj6373Au5DMEeFlOB3CZPvbYwdChtbxfFaJRu4OnouIM8UpqFUyq2RbcHLc nma6SQzf4I3UOKtq904avU1Fgz2PuAZJSOefvVHpo2aXm4lMxJGibDnoAWUZJaUCPpsm WbszgtAsNlcrU5Kh1TiDluJZ18kH7oNx8sPbz4bNDh2OzkECDvMoq/w6aw4pFJT5NvR6 OmVQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1736389831; x=1736994631; 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=L2pdotIvyMZQNnGmgTfsGf0xKAYx/XKZavKJSJfbFgY=; b=FzXySNB3hpJbQnMuOUBE6MbeA84cy2bIpEaHjxR8TtyNAvimNcHwBupzxZKpadZ3eI u6rUMBHe0AOlkZSbHVx7rX9KDseGDCSHcAFTZGmdsKJ4N8OwdDRt0eIVbQjDpdiy1/bg clMrB5Xe3AF+DaW+5vmolhoSYQQbDNW8j6T5LIVYKp6ssgrwj9Qb7jZzgr4u2AHDsY2n iHpe0LQqyjc57oT8l0fXIxRD+r7heXm1OAFDGcgNeJCP4pmxAnfuBxvRlwsrBRJag04N aeoGRMHEqAqX9F3UC4qqtpz46zU1dSs5najeFI04sBl6biDQC/qnWE59rS//iwUSnWJR 8DAg== X-Forwarded-Encrypted: i=1; AJvYcCVaKGJHsbQayhkNns2IfqYDXKfIKcg/IcGXA3qTDEJ12aveRghr4JWT5o8utq64eCDp2SphA4nj7RKrqc0=@vger.kernel.org X-Gm-Message-State: AOJu0YyrHnDwGy8USzTzn61ynkqfD/bxKEjMMhN9RnLcmd80dFFsVEt4 aqxnbaZW/e7JyRlH/fuMsetzFSanGZaSCHkeWmIx+YpAapHg529jM0rLgY7VYhsBiGkio5NOvrj J3w== X-Google-Smtp-Source: AGHT+IHWgi2ldN3a83aKZv2dDntq/xf/7vQGhigjGpu6Kf8lGzADe54dCpxgONH1NIDSqnEDQ0UO7ZABvv0= X-Received: from pjbnb3.prod.google.com ([2002:a17:90b:35c3:b0:2ee:3128:390f]) (user=surenb job=prod-delivery.src-stubby-dispatcher) by 2002:a17:90b:2748:b0:2f1:30c8:6e75 with SMTP id 98e67ed59e1d1-2f5490e89e0mr6525677a91.32.1736389830966; Wed, 08 Jan 2025 18:30:30 -0800 (PST) Date: Wed, 8 Jan 2025 18:30:10 -0800 In-Reply-To: <20250109023025.2242447-1-surenb@google.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 References: <20250109023025.2242447-1-surenb@google.com> X-Mailer: git-send-email 2.47.1.613.gc27f4b7a9f-goog Message-ID: <20250109023025.2242447-2-surenb@google.com> Subject: [PATCH v8 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, richard.weiyang@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, "Liam R. Howlett" 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 Reviewed-by: Liam R. Howlett --- 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 57b9e4dc4724..b040376ee81f 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 11b7eb3c8a28..a03c6f1ceb9e 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; @@ -1490,14 +1482,10 @@ 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