Date:   Wed, 15 Feb 2023 21:17:36 -0800
In-Reply-To: <20230216051750.3125598-1-surenb@google.com>
Mime-Version: 1.0
References: <20230216051750.3125598-1-surenb@google.com>
Message-ID: <20230216051750.3125598-22-surenb@google.com>
Subject: [PATCH v3 21/35] mm/mmap: write-lock adjacent VMAs if they can grow
 into unmapped area
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>
Content-Type: text/plain; charset="UTF-8"
Precedence: bulk

While unmapping VMAs, adjacent VMAs might be able to grow into the area
being unmapped. In such cases write-lock adjacent VMAs to prevent this
growth.

Signed-off-by: Suren Baghdasaryan <surenb@google.com>
---
 mm/mmap.c | 8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/mm/mmap.c b/mm/mmap.c
index 118b2246bba9..00f8c5798936 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -2399,11 +2399,13 @@ do_vmi_align_munmap(struct vma_iterator *vmi, struct vm_area_struct *vma,
 	 * down_read(mmap_lock) and collide with the VMA we are about to unmap.
 	 */
 	if (downgrade) {
-		if (next && (next->vm_flags & VM_GROWSDOWN))
+		if (next && (next->vm_flags & VM_GROWSDOWN)) {
+			vma_start_write(next);
 			downgrade = false;
-		else if (prev && (prev->vm_flags & VM_GROWSUP))
+		} else if (prev && (prev->vm_flags & VM_GROWSUP)) {
+			vma_start_write(prev);
 			downgrade = false;
-		else
+		} else
 			mmap_write_downgrade(mm);
 	}
 
-- 
2.39.1