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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 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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.