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Wed, 01 Mar 2023 10:42:59 -0800 (PST) MIME-Version: 1.0 References: <20230227173632.3292573-1-surenb@google.com> <20230227173632.3292573-19-surenb@google.com> In-Reply-To: From: Suren Baghdasaryan Date: Wed, 1 Mar 2023 10:42:48 -0800 Message-ID: Subject: Re: [PATCH v4 18/33] mm: write-lock VMAs before removing them from VMA tree To: Hyeonggon Yoo <42.hyeyoo@gmail.com> 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 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Rspam-User: X-Rspamd-Server: rspam04 X-Rspamd-Queue-Id: 4631114000A X-Stat-Signature: 735a3zkpa58qordej8z6d79z8a47o6uu X-HE-Tag: 1677696180-914889 X-HE-Meta: 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 4skLaS3K dydviLbar+9aVet4VGx5QGwwLrGLHiBPmH3HQ3ZmbEyQf4FxOHlEKy5N6XnWlq4LxbI31hPyw3ZfFDMnrLkYAA+t1OrsOWG4kb3YMSbIhxSnqHVwDlG2zO1NLBmLK/kwEZeKjT69b3njshKGFjiYE2OK22vYyPQHQT3XVd4iB+JmPiLjBkz/XNTsQZTUZAQODhKwsYfLs17t/QrDuVjEXAOT6fuuS/ajxRRSPPeYwfg+m5P/CaD0Crq4pIf3FhMaO6a9dJtfQ5mCb0Q0dYgcyOHFpH/sjttUNswZU0ilgRktrxNYHFk1LlsZUxI+6++YmWFG00UUCEfeyvHt17/IakmQBErczaGE4xDODNr/0pWK5zRb3rkjc7r3Y4PL39SpHnbVneRwekCmLNNeEuVC5vSnGSoga3lcYal0O 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 1, 2023 at 10:34=E2=80=AFAM Suren Baghdasaryan wrote: > > On Tue, Feb 28, 2023 at 11:57=E2=80=AFPM Hyeonggon Yoo <42.hyeyoo@gmail.c= om> wrote: > > > > 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, struc= t 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? > > We need to mark the VMA detached to avoid handling page fault in a > detached VMA. The possible scenario is: > > lock_vma_under_rcu > vma =3D mas_walk(&mas) > munmap_sidetree > vma_start_write= (vma) > > mas_store_gfp() // remove VMA from the tree > vma_end_write_a= ll() > vma_start_read(vma) > // we locked the VMA but it is not part of the tree anymore. > > So, marking the VMA locked before vma_end_write_all() and checking Sorry, I should have said "marking the VMA *detached* before vma_end_write_all() and checking vma->detached after vma_start_read() helps us avoid handling faults in the detached VMA." > vma->detached after vma_start_read() helps us avoid handling faults in > the detached VMA. > > > > > > > > 2) as VMAs that are going to be removed are already locked in v= ma_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_st= ruct *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 o= n MMU anyway. > > Ah, yes, you are right. We can safely remove the changes in nommu.c > Andrew, should I post a fixup or you can make the removal directly in > mm-unstable? > Thanks, > Suren. > > > > > > > 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 > > > > > > > > > > > > > > > -- > > To unsubscribe from this group and stop receiving emails from it, send = an email to kernel-team+unsubscribe@android.com. > >