linux-kernel - Re: [PATCH v4 5/6] mm: always lock new vma before inserting into vma tree

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Message-Id: <20230814121521.83c2dda21765757d272538b2@linux-foundation.org>
Date:   Mon, 14 Aug 2023 12:15:21 -0700
From:   Andrew Morton <akpm@...ux-foundation.org>
To:     Jann Horn <jannh@...gle.com>
Cc:     Suren Baghdasaryan <surenb@...gle.com>,
        torvalds@...ux-foundation.org, willy@...radead.org,
        liam.howlett@...cle.com, david@...hat.com, peterx@...hat.com,
        ldufour@...ux.ibm.com, vbabka@...e.cz, michel@...pinasse.org,
        jglisse@...gle.com, mhocko@...e.com, hannes@...xchg.org,
        dave@...olabs.net, hughd@...gle.com, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org, kernel-team@...roid.com
Subject: Re: [PATCH v4 5/6] mm: always lock new vma before inserting into
 vma tree

On Mon, 14 Aug 2023 16:54:01 +0200 Jann Horn <jannh@...gle.com> wrote:

> > @@ -403,6 +403,8 @@ static int vma_link(struct mm_struct *mm, struct vm_area_struct *vma)
> >
> >   vma_iter_store(&vmi, vma);
> >
> > + vma_start_write(vma);
> > +
> >   if (vma->vm_file) {
> >  mapping = vma->vm_file->f_mapping;
> >  i_mmap_lock_write(mapping);
> 
> The "vma_start_write()" has to be ordered before the
> "vma_iter_store(&vmi, vma)".

Thanks.  This?


--- a/mm/mmap.c~mm-always-lock-new-vma-before-inserting-into-vma-tree-fix
+++ a/mm/mmap.c
@@ -401,10 +401,10 @@ static int vma_link(struct mm_struct *mm
 	if (vma_iter_prealloc(&vmi, vma))
 		return -ENOMEM;
 
-	vma_iter_store(&vmi, vma);
-
 	vma_start_write(vma);
 
+	vma_iter_store(&vmi, vma);
+
 	if (vma->vm_file) {
 		mapping = vma->vm_file->f_mapping;
 		i_mmap_lock_write(mapping);
_