Package: procps Version: 2:3.3.16-5 Severity: normal File: /sbin/sysctl X-Debbugs-Cc: [email protected]
/proc/sys/vm/stat_refresh is a special file that if read or written (by root), triggers synchronization of all VM data from all CPUs, so other files (i.e. /proc/meminfo in particular) show up to date values. https://www.kernel.org/doc/Documentation/sysctl/vm.txt for more details. sysctl -a does read this file. strace: strace sysctl -a 2>&1 | grep 'refresh' stat("/proc/sys/vm/stat_refresh", {st_mode=S_IFREG|0600, st_size=0, ...}) = 0 stat("/proc/sys/vm/stat_refresh", {st_mode=S_IFREG|0600, st_size=0, ...}) = 0 openat(AT_FDCWD, "/proc/sys/vm/stat_refresh", O_RDONLY) = 5 However, in the presence of real time tasks, reading might block indefinitively, i.e.: sudo schedtool -R -p 98 -a 7 -e stress-ng -c 1 time cat /proc/sys/vm/stat_refresh This will never finish (I waited dozens of minutes). I would suggest adding a special case to sysctl to not read vm.stat_refresh. It produces no usable output, and reading it has side effects, thus should be avoided. Tested on Debian kernel Linux 5.9.11 with standard settings. Also it does feel like a regression, because I do found reports from the past that sysctl did not read vm.stat_refresh in the past, and done so on purpose: https://bugzilla.redhat.com/show_bug.cgi?id=1473207 As of the blocking indefinitively, I will look into contacting kernel devs about this issue, but even if this is fixed in the kernel, the sysctl should still not touch the /proc/sys/vm/stat_refresh file. Regards, Witold -- System Information: Debian Release: bullseye/sid APT prefers unstable-debug APT policy: (500, 'unstable-debug'), (500, 'unstable') Architecture: amd64 (x86_64) Foreign Architectures: i386 Kernel: Linux 5.9.0-4-amd64 (SMP w/32 CPU threads) Locale: LANG=en_US.UTF-8, LC_CTYPE=en_US.UTF-8 (charmap=UTF-8), LANGUAGE not set Shell: /bin/sh linked to /usr/bin/dash Init: systemd (via /run/systemd/system) LSM: AppArmor: enabled Versions of packages procps depends on: ii init-system-helpers 1.60 ii libc6 2.31-6 ii libncurses6 6.2+20201114-1 ii libncursesw6 6.2+20201114-1 ii libprocps8 2:3.3.16-5 ii libtinfo6 6.2+20201114-1 ii lsb-base 11.1.0 Versions of packages procps recommends: ii psmisc 23.3-1 procps suggests no packages. -- no debconf information
