Hi all,
Recently "memfd: improve userspace warnings for missing exec-related flags" was merged. On my system, this is a regression, not an improvement, because the entire 256k kernel log buffer (default on x86) is filled with these warnings and "__do_sys_memfd_create: 122 callbacks suppressed". I haven't investigated too closely, but the most likely cause is Wayland libraries.
This is too serious of a consequence for using an old API, especially considering how recently the flags were added. The vast majority of software has not had time to add the flags: glibc does not define the macros until 2.38 which was released less than one month ago, man-pages does not document the flags, and according to Debian Code Search, only systemd, stress-ng, and strace actually pass either of these flags.
Furthermore, since old kernels reject unknown flags, it's not just a matter of defining and passing the flag; every program needs to add logic to handle EINVAL and try again.
Some other way needs to be found to encourage userspace to add the flags; otherwise, this message will be patched out because the kernel log becomes unusable after running unupdated programs, which will still exist even after upstreams are fixed. In particular, AppImages, flatpaks, snaps, and similar app bundles contain vendored Wayland libraries which can be difficult or impossible to update.
Thanks, Alex.
On 8/30/23 17:52, Alex Xu (Hello71) wrote:
Hi all,
Recently "memfd: improve userspace warnings for missing exec-related flags" was merged. On my system, this is a regression, not an improvement, because the entire 256k kernel log buffer (default on x86) is filled with these warnings and "__do_sys_memfd_create: 122 callbacks suppressed". I haven't investigated too closely, but the most likely cause is Wayland libraries.
This is too serious of a consequence for using an old API, especially considering how recently the flags were added. The vast majority of software has not had time to add the flags: glibc does not define the macros until 2.38 which was released less than one month ago, man-pages does not document the flags, and according to Debian Code Search, only systemd, stress-ng, and strace actually pass either of these flags.
Furthermore, since old kernels reject unknown flags, it's not just a matter of defining and passing the flag; every program needs to add logic to handle EINVAL and try again.
Some other way needs to be found to encourage userspace to add the flags; otherwise, this message will be patched out because the kernel log becomes unusable after running unupdated programs, which will still exist even after upstreams are fixed. In particular, AppImages, flatpaks, snaps, and similar app bundles contain vendored Wayland libraries which can be difficult or impossible to update.
It's being reverted: https://lore.kernel.org/all/20230902230530.6B663C433C8@smtp.kernel.org/
Meanwhile stable should avoid backporting 434ed3350f57 ("memfd: improve userspace warnings for missing exec-related flags")
Thanks, Alex.
[TLDR: This mail in primarily relevant for Linux kernel regression tracking. See link in footer if these mails annoy you.]
On 04.09.23 15:31, Vlastimil Babka wrote:
On 8/30/23 17:52, Alex Xu (Hello71) wrote:
Hi all,
Recently "memfd: improve userspace warnings for missing exec-related flags" was merged. On my system, this is a regression, not an improvement, because the entire 256k kernel log buffer (default on x86) is filled with these warnings and "__do_sys_memfd_create: 122 callbacks suppressed". I haven't investigated too closely, but the most likely cause is Wayland libraries.
This is too serious of a consequence for using an old API, especially considering how recently the flags were added. The vast majority of software has not had time to add the flags: glibc does not define the macros until 2.38 which was released less than one month ago, man-pages does not document the flags, and according to Debian Code Search, only systemd, stress-ng, and strace actually pass either of these flags.
Furthermore, since old kernels reject unknown flags, it's not just a matter of defining and passing the flag; every program needs to add logic to handle EINVAL and try again.
Some other way needs to be found to encourage userspace to add the flags; otherwise, this message will be patched out because the kernel log becomes unusable after running unupdated programs, which will still exist even after upstreams are fixed. In particular, AppImages, flatpaks, snaps, and similar app bundles contain vendored Wayland libraries which can be difficult or impossible to update.
It's being reverted: https://lore.kernel.org/all/20230902230530.6B663C433C8@smtp.kernel.org/
in that case:
#regzbot fix: revert "memfd: improve userspace warnings for missing exec-related flags". #regzbot ignore-activity
Ciao, Thorsten (wearing his 'the Linux kernel's regression tracker' hat) -- Everything you wanna know about Linux kernel regression tracking: https://linux-regtracking.leemhuis.info/about/#tldr That page also explains what to do if mails like this annoy you.
linux-kselftest-mirror@lists.linaro.org
-
Alex Xu (Hello71) -
Linux regression tracking #update (Thorsten Leemhuis) -
Vlastimil Babka