CABA = Closest Alive Born Ancestor In Linux process tree we reparent children of a dying process to the reaper, thus loosing information in which subtree the child was originally born. This information can be useful to CRIU to restore process trees right. The idea of CABA tree is to keep reference to the closest "born" ancestor in the process tree. In simple case if our "born" parent dies (completely unhashed) CABA would then point to its "born" parent - our "born" grand-parent. So CABA is always referencing closest "born" (grand-)*parent in available processes. Please see "Add CABA tree to task_struct" for deeper explanation, and "tests: Add CABA selftest" for a small test and an actual example for which we might need CABA. Probably the original problem of restoring process tree with complex sessions can be resolved by allowing sessions copying, like we do for process group, but I'm not sure if that would be too secure to do it, and if there would not be another similar resource in future. So I prefere CABA. Also we can use CABA not only for CRIU for restoring processes, but in normal life when processes detach CABA will help to understand from which place in process tree they were originally started from sshd/crond or something else. Hope my idea is not completely insane =) I plan to have a talk on LPC 2022 about it https://lpc.events/event/16/contributions/1241/ CC: Eric Biederman <ebiederm@xxxxxxxxxxxx> CC: Kees Cook <keescook@xxxxxxxxxxxx> CC: Alexander Viro <viro@xxxxxxxxxxxxxxxxxx> CC: Ingo Molnar <mingo@xxxxxxxxxx> CC: Peter Zijlstra <peterz@xxxxxxxxxxxxx> CC: Juri Lelli <juri.lelli@xxxxxxxxxx> CC: Vincent Guittot <vincent.guittot@xxxxxxxxxx> CC: Dietmar Eggemann <dietmar.eggemann@xxxxxxx> CC: Steven Rostedt <rostedt@xxxxxxxxxxx> CC: Ben Segall <bsegall@xxxxxxxxxx> CC: Mel Gorman <mgorman@xxxxxxx> CC: Daniel Bristot de Oliveira <bristot@xxxxxxxxxx> CC: Valentin Schneider <vschneid@xxxxxxxxxx> CC: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> CC: linux-ia64@xxxxxxxxxxxxxxx CC: linux-kernel@xxxxxxxxxxxxxxx CC: linux-mm@xxxxxxxxx CC: linux-fsdevel@xxxxxxxxxxxxxxx CC: kernel@xxxxxxxxxx Pavel Tikhomirov (2): Add CABA tree to task_struct tests: Add CABA selftest arch/ia64/kernel/mca.c | 3 + fs/exec.c | 1 + fs/proc/array.c | 20 + include/linux/sched.h | 7 + init/init_task.c | 3 + kernel/exit.c | 21 + kernel/fork.c | 4 + tools/testing/selftests/Makefile | 1 + tools/testing/selftests/caba/.gitignore | 1 + tools/testing/selftests/caba/Makefile | 7 + tools/testing/selftests/caba/caba_test.c | 509 +++++++++++++++++++++++ tools/testing/selftests/caba/config | 1 + 12 files changed, 578 insertions(+) create mode 100644 tools/testing/selftests/caba/.gitignore create mode 100644 tools/testing/selftests/caba/Makefile create mode 100644 tools/testing/selftests/caba/caba_test.c create mode 100644 tools/testing/selftests/caba/config -- 2.37.1
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