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Fri, 04 Aug 2023 17:26:46 -0700 (PDT) MIME-Version: 1.0 References: <20230708191212.4147700-1-surenb@google.com> <20230708191212.4147700-3-surenb@google.com> <20230804214620.btgwhsszsd7rh6nf@f> In-Reply-To: From: Suren Baghdasaryan Date: Fri, 4 Aug 2023 17:26:33 -0700 Message-ID: Subject: Re: [PATCH v2 3/3] fork: lock VMAs of the parent process when forking To: Linus Torvalds Cc: Mateusz Guzik , akpm@linux-foundation.org, regressions@leemhuis.info, bagasdotme@gmail.com, jacobly.alt@gmail.com, willy@infradead.org, liam.howlett@oracle.com, david@redhat.com, peterx@redhat.com, ldufour@linux.ibm.com, linux-kernel@vger.kernel.org, linux-mm@kvack.org, linuxppc-dev@lists.ozlabs.org, linux-arm-kernel@lists.infradead.org, gregkh@linuxfoundation.org, regressions@lists.linux.dev, Jiri Slaby , =?UTF-8?Q?Holger_Hoffst=C3=A4tte?= , stable@vger.kernel.org Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Rspamd-Queue-Id: 741D1140024 X-Rspam-User: X-Rspamd-Server: rspam05 X-Stat-Signature: 4hyb6mpkqz66ysykiodwcdwdc47tfipx X-HE-Tag: 1691195207-169998 X-HE-Meta: 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 a22sktNk S/mwiRSW4RtprAD4Z7zTavMOrlDXEcawR7l/7Dg6F/Nu2YfiFltzWiIqdwbhDxS8I1Pxj5BsG0DC3sIWV9ycHJlPukQ5FX6t5fR2pF0TYKOccSw4NISTS1KlCyj7QFeNGwV8BTE5JJiK/HN7e5XcmUx5xaMvFoDOEQi1mT523/XWjn+SX8TJvMITO0L7dIccOl4g+festDVK7FQyUQnWBaR/wuX3CVoRcdCoK3p7fD7Rw4z0K8SGfVX4u+x03k2m8CDG2hjj3GMl94IsAH320mt8XvSVBhtjyJsXwQU/AK9cEIf5KFfqzb8vSSyB/gmcJ0/LgzmFq10ww6cj1GS0W47Pl+BSdPcv098wNoKfIYHGcsUra5kN/3RZejudfvjxOO9dmm69eM6KgDC6wiVLlSPlWDXyYsCV7GroR29O/76vbLBOs2ceuFNpX7w== 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 Fri, Aug 4, 2023 at 5:15=E2=80=AFPM Linus Torvalds wrote: > > On Fri, 4 Aug 2023 at 16:25, Mateusz Guzik wrote: > > > > I know of these guys, I think they are excluded as is -- they go > > through access_remote_vm, starting with: > > if (mmap_read_lock_killable(mm)) > > return 0; > > > > while dup_mmap already write locks the parent's mm. > > Oh, you're only worried about vma_start_write()? > > That's a non-issue. It doesn't take the lock normally, since it starts of= f with > > if (__is_vma_write_locked(vma, &mm_lock_seq)) > return; > > which catches on the lock sequence number already being set. That check will prevent re-locking but if vma is not already locked then the call will proceed with obtaining the lock and setting vma->vm_lock_seq to mm->mm_lock_seq. > > So no extra locking there. > > Well, technically there's extra locking because the code stupidly > doesn't initialize new vma allocations to the right sequence number, > but that was talked about here: > > https://lore.kernel.org/all/CAHk-=3DwiCrWAoEesBuoGoqqufvesicbGp3cX0Ly= KgEvsFaZNpDA@mail.gmail.com/ > > and it's a separate issue. > > Linus