Date:   Wed, 15 Feb 2023 21:17:32 -0800
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Subject: [PATCH v3 17/35] mm/mmap: write-lock VMA before shrinking or
 expanding it
From:   Suren Baghdasaryan <surenb@google.com>
To:     akpm@linux-foundation.org
Cc:     michel@lespinasse.org, jglisse@google.com, mhocko@suse.com,
        vbabka@suse.cz, hannes@cmpxchg.org, mgorman@techsingularity.net,
        dave@stgolabs.net, willy@infradead.org, liam.howlett@oracle.com,
        peterz@infradead.org, ldufour@linux.ibm.com, paulmck@kernel.org,
        mingo@redhat.com, will@kernel.org, luto@kernel.org,
        songliubraving@fb.com, peterx@redhat.com, david@redhat.com,
        dhowells@redhat.com, hughd@google.com, bigeasy@linutronix.de,
        kent.overstreet@linux.dev, punit.agrawal@bytedance.com,
        lstoakes@gmail.com, peterjung1337@gmail.com, rientjes@google.com,
        chriscli@google.com, axelrasmussen@google.com, joelaf@google.com,
        minchan@google.com, rppt@kernel.org, jannh@google.com,
        shakeelb@google.com, tatashin@google.com, edumazet@google.com,
        gthelen@google.com, gurua@google.com, arjunroy@google.com,
        soheil@google.com, leewalsh@google.com, posk@google.com,
        michalechner92@googlemail.com, linux-mm@kvack.org,
        linux-arm-kernel@lists.infradead.org,
        linuxppc-dev@lists.ozlabs.org, x86@kernel.org,
        linux-kernel@vger.kernel.org, kernel-team@android.com,
        Suren Baghdasaryan <surenb@google.com>
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Precedence: bulk

vma_expand and vma_shrink change VMA boundaries. Expansion might also
result in freeing of an adjacent VMA. Write-lock affected VMAs to prevent
concurrent page faults.

Signed-off-by: Suren Baghdasaryan <surenb@google.com>
---
 mm/mmap.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/mm/mmap.c b/mm/mmap.c
index ec2f8d0af280..f079e5bbcd57 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -674,6 +674,9 @@ int vma_expand(struct vma_iterator *vmi, struct vm_area_struct *vma,
 		ret = dup_anon_vma(vma, next);
 		if (ret)
 			return ret;
+
+		/* Lock the VMA  before removing it */
+		vma_start_write(next);
 	}
 
 	init_multi_vma_prep(&vp, vma, NULL, remove_next ? next : NULL, NULL);
@@ -686,6 +689,7 @@ int vma_expand(struct vma_iterator *vmi, struct vm_area_struct *vma,
 	if (vma_iter_prealloc(vmi))
 		goto nomem;
 
+	vma_start_write(vma);
 	vma_adjust_trans_huge(vma, start, end, 0);
 	/* VMA iterator points to previous, so set to start if necessary */
 	if (vma_iter_addr(vmi) != start)
@@ -725,6 +729,7 @@ int vma_shrink(struct vma_iterator *vmi, struct vm_area_struct *vma,
 	if (vma_iter_prealloc(vmi))
 		return -ENOMEM;
 
+	vma_start_write(vma);
 	init_vma_prep(&vp, vma);
 	vma_adjust_trans_huge(vma, start, end, 0);
 	vma_prepare(&vp);
-- 
2.39.1