Linux Kernel 5.5 eventually eliminates code that supports sysctl system calls, which have been outof use for about a decade and currently have no impact on modern systems with any architecture. Linux sysctl system calls have long been not recommended for use, nor are they recommended with the sysctl interface exposed through /proc/sys, which is the preferred method for reading/setting kernel system properties.
The change swashes of Linux Kernel 5.5 do not involve /proc/sys support, but will simply remove system calls with sysctl binary interfaces on Linux that have not been used for many years.
The Linux kernel team said in an email that it was understood that no one should have enabled the sysctl system call, and that it would not be ruled out that it was still enabled in a small number of defconfigs, but this was also very rare. If any users want this system call, they may need to restore the patch.
In fact, as early as 2011, they wanted to delete the code, but they couldn’t completely remove it because they needed to be compatible. At the time, the rest of the code was meant to be compatible with the old C library, but now anyone who built Linux 5.5 doesn’t want to run super-old libc.
Eric W. Biederman wrote a patch that removed the system call, noting that previously “linux-next has a new xtensa defconfig that allows the system to call this loop, but the code maintainer replied that it was not intentionally enabled.” Starting with today’s linux-next tree, defconfig no longer enables system calls.