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Howlett" , LKML , linux-mm@kvack.org, Andrew Morton , Lokesh Gidra , Alistair Popple Subject: Re: [PATCH] mm: Always sanity check anon_vma first for per-vma locks Message-ID: References: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Rspamd-Queue-Id: CAD57160022 X-Rspam-User: X-Stat-Signature: aqmbx519eq11hiwrjixw1agydorapfh5 X-Rspamd-Server: rspam03 X-HE-Tag: 1712935910-407531 X-HE-Meta: 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 lMSVys4s HV5+XujLo0ajKIvAp6y+T4gtfVE4rvd3qlXtxP308ZM3cg5TDZ43/IR+6dCwEbdkxBqgE7ZsM5wcGkeO8KU5uJWDdhVxrOXpJA3hGOUZx+Yerjx9+8OHmw6GAni+ZDVmJIMumHMn/R5u2I8hMQ9ZsQsJEjhHuRQPCk8ZItkEd5uXW9TOxI3lFul17WQ== X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Fri, Apr 12, 2024 at 04:19:27PM +0100, Matthew Wilcox wrote: > On Fri, Apr 12, 2024 at 09:53:29AM -0500, Suren Baghdasaryan wrote: > > Unless vmf_anon_prepare() already explains why vma->anon_vma poses a > > problem for per-vma locks, we should have an explanation there. This > > comment would serve that purpose IMO. > > I'll do you one better; here's some nice kernel-doc for > vmd_anon_prepare(): And here's a followup patch to fix some minor issues in uffd. - Rename lock_vma() to uffd_lock_vma() because it really is uffd specific. - Remove comment referencing unlock_vma() which doesn't exist. - Fix the comment about lock_vma_under_rcu() which I just made incorrect. diff --git a/mm/userfaultfd.c b/mm/userfaultfd.c index f6267afe65d1..a32171158c38 100644 --- a/mm/userfaultfd.c +++ b/mm/userfaultfd.c @@ -56,17 +56,16 @@ struct vm_area_struct *find_vma_and_prepare_anon(struct mm_struct *mm, #ifdef CONFIG_PER_VMA_LOCK /* - * lock_vma() - Lookup and lock vma corresponding to @address. + * uffd_lock_vma() - Lookup and lock vma corresponding to @address. * @mm: mm to search vma in. * @address: address that the vma should contain. * - * Should be called without holding mmap_lock. vma should be unlocked after use - * with unlock_vma(). + * Should be called without holding mmap_lock. * * Return: A locked vma containing @address, -ENOENT if no vma is found, or * -ENOMEM if anon_vma couldn't be allocated. */ -static struct vm_area_struct *lock_vma(struct mm_struct *mm, +static struct vm_area_struct *uffd_lock_vma(struct mm_struct *mm, unsigned long address) { struct vm_area_struct *vma; @@ -74,9 +73,8 @@ static struct vm_area_struct *lock_vma(struct mm_struct *mm, vma = lock_vma_under_rcu(mm, address); if (vma) { /* - * lock_vma_under_rcu() only checks anon_vma for private - * anonymous mappings. But we need to ensure it is assigned in - * private file-backed vmas as well. + * We know we're going to need to use anon_vma, so check + * that early. */ if (!(vma->vm_flags & VM_SHARED) && unlikely(!vma->anon_vma)) vma_end_read(vma); @@ -107,7 +105,7 @@ static struct vm_area_struct *uffd_mfill_lock(struct mm_struct *dst_mm, { struct vm_area_struct *dst_vma; - dst_vma = lock_vma(dst_mm, dst_start); + dst_vma = uffd_lock_vma(dst_mm, dst_start); if (IS_ERR(dst_vma) || validate_dst_vma(dst_vma, dst_start + len)) return dst_vma; @@ -1437,7 +1435,7 @@ static int uffd_move_lock(struct mm_struct *mm, struct vm_area_struct *vma; int err; - vma = lock_vma(mm, dst_start); + vma = uffd_lock_vma(mm, dst_start); if (IS_ERR(vma)) return PTR_ERR(vma); @@ -1452,7 +1450,7 @@ static int uffd_move_lock(struct mm_struct *mm, } /* - * Using lock_vma() to get src_vma can lead to following deadlock: + * Using uffd_lock_vma() to get src_vma can lead to following deadlock: * * Thread1 Thread2 * ------- ------- @@ -1474,7 +1472,7 @@ static int uffd_move_lock(struct mm_struct *mm, err = find_vmas_mm_locked(mm, dst_start, src_start, dst_vmap, src_vmap); if (!err) { /* - * See comment in lock_vma() as to why not using + * See comment in uffd_lock_vma() as to why not using * vma_start_read() here. */ down_read(&(*dst_vmap)->vm_lock->lock);