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From: "Yajun Deng" Message-ID: <3c452d5db5b3d5879160ab62a9e0ac4481a6298a@linux.dev> TLS-Required: No Subject: Re: [PATCH] mm/rmap: remove unnecessary page_table_lock To: "David Hildenbrand" , akpm@linux-foundation.org Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org In-Reply-To: References: <20240422105212.1485788-1-yajun.deng@linux.dev> X-Migadu-Flow: FLOW_OUT X-Rspam-User: X-Rspamd-Server: rspam08 X-Rspamd-Queue-Id: 347E3180006 X-Stat-Signature: ays3ra8rwosb7ef34p3orujmpcisjden X-HE-Tag: 1713858808-763307 X-HE-Meta: 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 E60X2fLg AiddM3fc8eRzqNSeGw1e3nL0JMs9ciqLpv2vKc1k3TJQQfONnNPkcPA68SOhPZfbUfd2PjtT7geQUVXqAoRdCdJ9zD+EdCc/JuPHYQNqthg5CCqoi7BgWpbX0u/gQwYZ2iq8xTSVcLPy7tO80HNQj//jGrBhDIR7yyL3u X-Bogosity: Ham, tests=bogofilter, spamicity=0.000004, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: April 22, 2024 at 7:24 PM, "David Hildenbrand" wrote: >=20 >=20On 22.04.24 12:52, Yajun Deng wrote: >=20 >=20>=20 >=20> page_table_lock is a lock that for page table, we won't change page > >=20 >=20> table in __anon_vma_prepare(). As we can see, it works well in > >=20 >=20> anon_vma_clone(). They do the same operation. > >=20 >=20 > We are reusing mm->page_table_lock to serialize, not the *actual* low-l= evel page table locks that really protect PTEs. >=20 >=20With that locking gone, there would be nothing protection vma->anon_v= ma. >=20 >=20Note that anon_vma_clone() is likely called with the mmap_lock held i= n write mode, which is not the case for __anon_vma_prepare() ... Yes, anon_vma_clone() is called with the mmap_lock held. I added mmap_ass= ert_write_locked(dst->vm_mm) to prove it. I added mmap_assert_write_locked(vma->vm_mm) in __anon_vma_prepare() at t= he same time, it shows __anon_vma_prepare() is also called with the mmap_lock held too. >=20 >=20I think this change is wrong. >=20 >=20-- Cheers, >=20 >=20David / dhildenb >