From: Thomas Gleixner Date: Mon, 2 Feb 2026 09:39:50 +0000 (+0100) Subject: sched/mmcid: Drop per CPU CID immediately when switching to per task mode X-Git-Tag: v6.19~5^2~1 X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=007d84287c7466ca68a5809b616338214dc5b77b;p=thirdparty%2Fkernel%2Flinux.git sched/mmcid: Drop per CPU CID immediately when switching to per task mode When a exiting task initiates the switch from per CPU back to per task mode, it has already dropped its CID and marked itself inactive. But a leftover from an earlier iteration of the rework then reassigns the per CPU CID to the exiting task with the transition bit set. That's wrong as the task is already marked CID inactive, which means it is inconsistent state. It's harmless because the CID is marked in transit and therefore dropped back into the pool when the exiting task schedules out either through preemption or the final schedule(). Simply drop the per CPU CID when the exiting task triggered the transition. Fixes: fbd0e71dc370 ("sched/mmcid: Provide CID ownership mode fixup functions") Signed-off-by: Thomas Gleixner Signed-off-by: Peter Zijlstra (Intel) Reviewed-by: Mathieu Desnoyers Link: https://patch.msgid.link/20260201192835.032221009@kernel.org --- diff --git a/kernel/sched/core.c b/kernel/sched/core.c index 858028300c5f..854984967fe2 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -10727,8 +10727,14 @@ void sched_mm_cid_exit(struct task_struct *t) scoped_guard(raw_spinlock_irq, &mm->mm_cid.lock) { if (!__sched_mm_cid_exit(t)) return; - /* Mode change required. Transfer currents CID */ - mm_cid_transit_to_task(current, this_cpu_ptr(mm->mm_cid.pcpu)); + /* + * Mode change. The task has the CID unset + * already. The CPU CID is still valid and + * does not have MM_CID_TRANSIT set as the + * mode change has just taken effect under + * mm::mm_cid::lock. Drop it. + */ + mm_drop_cid_on_cpu(mm, this_cpu_ptr(mm->mm_cid.pcpu)); } mm_cid_fixup_cpus_to_tasks(mm); return;