From 0d6526f82c3cdefcca47f73f5fc08dc6f335eac6 Mon Sep 17 00:00:00 2001 From: Tim Chen Date: Mon, 21 Sep 2026 17:37:22 -0700 Subject: sched/cache: Keep nr_pref_llc_running in the runnable domain, to fix LLC mis-scheduling bug alb_break_llc() decides whether to break LLC preference during active load balance. It does so by testing that every runnable fair task on the source rq prefers its LLC: env->src_rq->nr_pref_llc_running == env->src_rq->cfs.h_nr_runnable But the two counters cover different sets. nr_pref_llc_running is updated in account_llc_enqueue()/account_llc_dequeue(), next to cfs_rq->nr_queued, so it follows queued tasks. h_nr_runnable is updated in set_delayed()/ clear_delayed() and drops delay-dequeued tasks. So under DELAY_DEQUEUE, a preferring task that goes to sleep stays counted in nr_pref_llc_running while h_nr_runnable falls. The equality then breaks, alb_break_llc() returns false, and active balance is free to pull a task off its preferred LLC. Active balance only moves runnable tasks, and this is the only LLC check it consults: once the stopper runs, LBF_ACTIVE_LB skips the per-task test in can_migrate_task(). The runnable set is the one we want. Fix it on the counter side. A task should be counted in nr_pref_llc_running exactly while it is both queued on its preferred LLC (pref_llc_queued) and runnable (!sched_delayed). Define that membership once in task_pref_llc_runnable(), and adjust the counter only through pref_llc_running_inc()/pref_llc_running_dec() from the four sites that change either input: account_llc_enqueue(), account_llc_dequeue(), set_delayed() and clear_delayed(). Gating every update on the same predicate keeps the delay, wake and dequeue paths from double-counting or underflowing; see the comments at those sites for the ordering. nr_llc_running and sd->llc_counts are not touched and stay on queued semantics. Fixes: 714059f79ff0 ("sched/cache: Handle moving single tasks to/from their preferred LLC") Closes: https://lore.kernel.org/lkml/20260827135000.735138-1-zhanxusheng@xiaomi.com/ Reported-by: Zhan Xusheng Suggested-by: Chen Yu Signed-off-by: Tim Chen Signed-off-by: Peter Zijlstra (Intel) Signed-off-by: Ingo Molnar Reviewed-by: Kayra Cizmeci Cc: # v7.2.x Link: https://patch.msgid.link/06af61afedac32e6477f57feb4d658f6c411c3af.1790035273.git.tim.c.chen@linux.intel.com --- Documentation/process/conclave.rst | 41 ++++++++++++++++++++++++++++++++++++++ 1 file changed, 41 insertions(+) create mode 100644 Documentation/process/conclave.rst (limited to 'Documentation/process/conclave.rst') diff --git a/Documentation/process/conclave.rst b/Documentation/process/conclave.rst new file mode 100644 index 000000000..6a1234f54 --- /dev/null +++ b/Documentation/process/conclave.rst @@ -0,0 +1,41 @@ +.. SPDX-License-Identifier: GPL-2.0 + +Linux kernel project continuity +=============================== + +The Linux kernel development project is widely distributed, with over +100 maintainers each working to keep changes moving through their own +repositories. The final step, though, is a centralized one where changes +are pulled into the mainline repository. That is normally done by Linus +Torvalds but, as was demonstrated by the 4.19 release in 2018, there are +others who can do that work when the need arises. + +Should the maintainers of that repository become unwilling or unable to +do that work going forward (including facilitating a transition), the +project will need to find one or more replacements without delay. The +process by which that will be done is listed below. $ORGANIZER is the +last Maintainer Summit organizer or the current Linux Foundation (LF) +Technical Advisory Board (TAB) Chair as a backup. + +- Within 72 hours, $ORGANIZER will open a discussion with the invitees + of the most recently concluded Maintainers Summit. A meeting of those + invitees and the TAB, either online or in-person, will be set as soon + as possible in a way that maximizes the number of people who can + participate. + +- If there has been no Maintainers Summit in the last 15 months, the set of + invitees for this meeting will be determined by the TAB. + +- The invitees to this meeting may bring in other maintainers as needed. + +- This meeting, chaired by $ORGANIZER, will consider options for the + ongoing management of the top-level kernel repository consistent with + the expectation that it maximizes the long term health of the project + and its community. + +- Within two weeks, a representative of this group will communicate to the + broader community, using the ksummit@lists.linux.dev mailing list, what + the next steps will be. + +The Linux Foundation, as guided by the TAB, will take the steps +necessary to support and implement this plan. -- cgit v1.3.1