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Tue, 28 Feb 2023 23:56:51 -0800 (PST) Date: Wed, 1 Mar 2023 07:56:36 +0000 From: Hyeonggon Yoo <42.hyeyoo@gmail.com> To: Suren Baghdasaryan Cc: akpm@linux-foundation.org, 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 Subject: Re: [PATCH v4 18/33] mm: write-lock VMAs before removing them from VMA tree Message-ID: References: <20230227173632.3292573-1-surenb@google.com> <20230227173632.3292573-19-surenb@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Rspam-User: X-Rspamd-Server: rspam03 X-Stat-Signature: czmwknir6otirrbb6m9w8aq71zudmsrm X-Rspamd-Queue-Id: 57E5714000E X-HE-Tag: 1677657425-760348 X-HE-Meta: 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 gD+eYY4F NmtPNkgZuCcTXcYKWXQT5LNnnl7UpaCQuspk3wRz12fZFHgANjClu2LkP2NDq4qblOT2pOdbNYdQrKzMvqDP7XnSv+x+zNT4cR+/oTmhCKRFkmPI8J7hXQAeYYX9m4bHu4jfDUyKCiKqKhcgT8OkirYS2wRvzEL0k/JHL+Ak65oVoD/uAWC5128TtEpvelpfjsPJ1B5zU6BUFLTwnqAEGoNvdyyEEbRMS5zcYCtZqj1OK2vLE8ChrQO7q8NHU61PNc1/iLRaVoijhTrzQ3IVYY5L1v8SfH298bXp6fMttILzE9yWvkcsiiPLFIYSH8i9VZETwvC4T3OKKN4MaKB1iQP1NuYUsGcuhmQ6e26Tzq8zf9TFyRbljI0SmjLUywh5UEhtgWPUTTWoIgvAmBX4qlHmbcmQbMAmeJTEFoPqYxqxA4MJt1SpPLC5ayuy7sYEL+SQlEuYjEpfBx0DcrUXMKZ2trSCAzI+YuRLL9OSiQoZ59pI= X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Wed, Mar 01, 2023 at 07:43:33AM +0000, Hyeonggon Yoo wrote: > On Mon, Feb 27, 2023 at 09:36:17AM -0800, Suren Baghdasaryan wrote: > > Write-locking VMAs before isolating them ensures that page fault > > handlers don't operate on isolated VMAs. > > > > Signed-off-by: Suren Baghdasaryan > > --- > > mm/mmap.c | 1 + > > mm/nommu.c | 5 +++++ > > 2 files changed, 6 insertions(+) > > > > diff --git a/mm/mmap.c b/mm/mmap.c > > index 1f42b9a52b9b..f7ed357056c4 100644 > > --- a/mm/mmap.c > > +++ b/mm/mmap.c > > @@ -2255,6 +2255,7 @@ int split_vma(struct vma_iterator *vmi, struct vm_area_struct *vma, > > static inline int munmap_sidetree(struct vm_area_struct *vma, > > struct ma_state *mas_detach) > > { > > + vma_start_write(vma); > > mas_set_range(mas_detach, vma->vm_start, vma->vm_end - 1); > > I may be missing something, but have few questions: > > 1) Why does a writer need to both write-lock a VMA and mark the VMA detached > when unmapping it, isn't it enough to just only write-lock a VMA? > > 2) as VMAs that are going to be removed are already locked in vma_prepare(), > so I think this hunk could be dropped? After sending this just realized that I did not consider simple munmap case :) But I still think 1) and 3) are valid question. > > > if (mas_store_gfp(mas_detach, vma, GFP_KERNEL)) > > return -ENOMEM; > > diff --git a/mm/nommu.c b/mm/nommu.c > > index 57ba243c6a37..2ab162d773e2 100644 > > --- a/mm/nommu.c > > +++ b/mm/nommu.c > > @@ -588,6 +588,7 @@ static int delete_vma_from_mm(struct vm_area_struct *vma) > > current->pid); > > return -ENOMEM; > > } > > + vma_start_write(vma); > > cleanup_vma_from_mm(vma); > > 3) I think this hunk could be dropped as Per-VMA lock depends on MMU anyway. > > Thanks, > Hyeonggon > > > > > /* remove from the MM's tree and list */ > > @@ -1519,6 +1520,10 @@ void exit_mmap(struct mm_struct *mm) > > */ > > mmap_write_lock(mm); > > for_each_vma(vmi, vma) { > > + /* > > + * No need to lock VMA because this is the only mm user and no > > + * page fault handled can race with it. > > + */ > > cleanup_vma_from_mm(vma); > > delete_vma(mm, vma); > > cond_resched(); > > -- > > 2.39.2.722.g9855ee24e9-goog > > > > >