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Tue, 28 Feb 2023 23:43:48 -0800 (PST) Date: Wed, 1 Mar 2023 07:43:33 +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: <20230227173632.3292573-19-surenb@google.com> X-Rspam-User: X-Rspamd-Server: rspam03 X-Stat-Signature: rodfdk6ziqftrni798y3g7qqea4hig55 X-Rspamd-Queue-Id: B469040016 X-HE-Tag: 1677656630-551519 X-HE-Meta: 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 l08IUQCe XRF1w707O+O5er8yKEt+TQOwUf5lDlbsSnnlJTs7LC1YtsOMg9d8EZC0Cp8kyLyq5nbJR8WioZ8Z6DI6+Ydkd/hXiG2FlCN4xxcFFiT5Ph1p+onh9QjkYVgCNk154SJpo807UAGAIEG9uQ6yjtNvnhBpbpd5gbWimJZDVX97kMRii15A+ilSQzNhwOvm6M7Ac9e0Lk1nwgVCXR9+1sbiacQEBP5VdeqX+YrK6ONdwECQ+NLJSEHca6+Fcg4Krg4J2ccnTauiYGFzYIISjde4tVhdD4h161xEOM/JVB4+b27sNMHAyfSQXHIgGfM9xncv7/bkXfLeoPxIir6MNPTaPqUtijX3lM0TD8GZidWR8LyVEa1QNwAgl2glyePhd/CrBFaHQuBL9+cpAt9BdLh9/TZ5cclrMBtnVSU11j6YR26ZMkHLbrEfiIitTL2a41SXMSQSsW16YsneRkShj0zMqj75LET2zjqvI5yNm 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 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? > 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 > >