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Hermes SMTP Server) with ESMTPA ID 0bd111ed5816a0df5a4f025ef033cea4; Wed, 30 Aug 2023 15:52:37 +0000 (UTC) Date: Wed, 30 Aug 2023 11:52:33 -0400 From: "Alex Xu (Hello71)" Subject: Don't fill the kernel log with memfd_create messages To: Christian Brauner , Aleksa Sarai Cc: Andrew Morton , Shuah Khan , Jeff Xu , Kees Cook , Daniel Verkamp , Dominique Martinet , stable@vger.kernel.org, linux-api@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, linux-kselftest@vger.kernel.org MIME-Version: 1.0 Message-Id: <1693408388.rwssx8r1h9.none@localhost> Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable References: <1693408388.rwssx8r1h9.none.ref@localhost> X-Mailer: WebService/1.1.21763 mail.backend.jedi.jws.acl:role.jedi.acl.token.atz.jws.hermes.yahoo X-Rspamd-Queue-Id: 71E36160004 X-Rspam-User: X-Stat-Signature: j9ftzwhwo48xfhxwmg1bjmnocnn59oaw X-Rspamd-Server: rspam03 X-HE-Tag: 1693410762-467717 X-HE-Meta: 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 T6oGcf9t Z+Gh81Z1HV0WRyMw9FatF6NV92cKm81wJ/4soHTYVyBCVCXaLkTFP1M3QLjjQXZo+IiizgwdopRu5R+FFccfcvreYHqqE0OWUnPRgba754yu3HgEUnA1h7yQQIbqnn0fOxQlGO3XdFT0P+YIWUcx1QEgmqrxtdPiy8g0UMrmeO7YLqQCiIKzgcfxQ64zS4IrXyrwE5Ih309gR4f/zHDxeyVwPIgKP0FW34mzDi++R8WxPle5s76nddQMH68AQsIguRsymSy5y/P4qzBn41JoYNDYU0A== 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: Hi all, Recently "memfd: improve userspace warnings for missing exec-related=20 flags" was merged. On my system, this is a regression, not an=20 improvement, because the entire 256k kernel log buffer (default on x86)=20 is filled with these warnings and "__do_sys_memfd_create: 122 callbacks=20 suppressed". I haven't investigated too closely, but the most likely=20 cause is Wayland libraries. This is too serious of a consequence for using an old API, especially=20 considering how recently the flags were added. The vast majority of=20 software has not had time to add the flags: glibc does not define the=20 macros until 2.38 which was released less than one month ago, man-pages=20 does not document the flags, and according to Debian Code Search, only=20 systemd, stress-ng, and strace actually pass either of these flags. Furthermore, since old kernels reject unknown flags, it's not just a=20 matter of defining and passing the flag; every program needs to=20 add logic to handle EINVAL and try again. Some other way needs to be found to encourage userspace to add the=20 flags; otherwise, this message will be patched out because the kernel=20 log becomes unusable after running unupdated programs, which will still=20 exist even after upstreams are fixed. In particular, AppImages,=20 flatpaks, snaps, and similar app bundles contain vendored Wayland=20 libraries which can be difficult or impossible to update. Thanks, Alex.