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For the init task's first execve, this > causes a problem: > > 1. current->mm is NULL (kernel threads don't have an mm) > 2. sched_mm_cid_before_execve() exits early because mm is NULL > 3. exec_binprm() fails (e.g., ENOENT for missing script interpreter) > 4. sched_mm_cid_after_execve() is called with mm still NULL > 5. sched_mm_cid_fork() is called unconditionally, triggering WARN_ON > > This is easily reproduced by booting with an init that is a shell script > (#!/bin/sh) where the interpreter doesn't exist in the initramfs. > > Fix this by checking if t->mm is NULL before calling sched_mm_cid_fork(), > matching the behavior of sched_mm_cid_before_execve() which already > handles this case via sched_mm_cid_exit()'s early return. > > Fixes: b0c3d51b54f8 ("sched/mmcid: Provide precomputed maximal value") > Cc: Thomas Gleixner > Signed-off-by: Cong Wang Thanks for the detailed explanation. Indeed, the offending commit removes a pre-existing NULL mm check: void sched_mm_cid_after_execve(struct task_struct *t) { - struct mm_struct *mm = t->mm; - - if (!mm) - return; Reviewed-by: Mathieu Desnoyers Thomas, Peter, Ingo, can we fast-track this fix for upstream ? Thanks, Mathieu -- Mathieu Desnoyers EfficiOS Inc. https://www.efficios.com