Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
From:   "Kirill A. Shutemov" <kirill@shutemov.name>
To:     Andrew Morton <akpm@linux-foundation.org>, x86@kernel.org,
        Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>,
        "H. Peter Anvin" <hpa@zytor.com>, Borislav Petkov <bp@alien8.de>,
        Peter Zijlstra <peterz@infradead.org>,
        Andy Lutomirski <luto@amacapital.net>,
        David Howells <dhowells@redhat.com>
Cc:     Kees Cook <keescook@chromium.org>,
        Dave Hansen <dave.hansen@intel.com>,
        Kai Huang <kai.huang@linux.intel.com>,
        Jacob Pan <jacob.jun.pan@linux.intel.com>,
        Alison Schofield <alison.schofield@intel.com>,
        linux-mm@kvack.org, kvm@vger.kernel.org, keyrings@vger.kernel.org,
        linux-kernel@vger.kernel.org,
        "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
Subject: [PATCHv2 22/59] mm/rmap: Clear vma->anon_vma on unlink_anon_vmas()
Date:   Wed, 31 Jul 2019 18:07:36 +0300
Message-Id: <20190731150813.26289-23-kirill.shutemov@linux.intel.com>
In-Reply-To: <20190731150813.26289-1-kirill.shutemov@linux.intel.com>
References: <20190731150813.26289-1-kirill.shutemov@linux.intel.com>
MIME-Version: 1.0
Content-Transfer-Encoding: 8bit
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

If all pages in the VMA got unmapped there's no reason to link it into
original anon VMA hierarchy: it cannot possibly share any pages with
other VMA.

Set vma->anon_vma to NULL on unlink_anon_vmas(). With the change VMA
can be reused. The new anon VMA will be allocated on the first fault.

Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
---
 mm/rmap.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/mm/rmap.c b/mm/rmap.c
index e5dfe2ae6b0d..911367b5fb40 100644
--- a/mm/rmap.c
+++ b/mm/rmap.c
@@ -400,8 +400,10 @@ void unlink_anon_vmas(struct vm_area_struct *vma)
 		list_del(&avc->same_vma);
 		anon_vma_chain_free(avc);
 	}
-	if (vma->anon_vma)
+	if (vma->anon_vma) {
 		vma->anon_vma->degree--;
+		vma->anon_vma = NULL;
+	}
 	unlock_anon_vma_root(root);
 
 	/*
-- 
2.21.0