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/index.rst | 114 ++++++++++++++++++++++++++++++++++++++++ 1 file changed, 114 insertions(+) create mode 100644 Documentation/process/index.rst (limited to 'Documentation/process/index.rst') diff --git a/Documentation/process/index.rst b/Documentation/process/index.rst new file mode 100644 index 000000000..aa7c959a5 --- /dev/null +++ b/Documentation/process/index.rst @@ -0,0 +1,114 @@ +.. raw:: latex + + \renewcommand\thesection* + \renewcommand\thesubsection* + +.. _process_index: + +============================================= +Working with the kernel development community +============================================= + +So you want to be a Linux kernel developer? Welcome! While there is a lot +to be learned about the kernel in a technical sense, it is also important +to learn about how our community works. Reading these documents will make +it much easier for you to get your changes merged with a minimum of +trouble. + +An introduction to how kernel development works +----------------------------------------------- + +Read these documents first: an understanding of the material here will ease +your entry into the kernel community. + +.. toctree:: + :maxdepth: 1 + + howto + development-process + submitting-patches + submit-checklist + +Tools and technical guides for kernel developers +------------------------------------------------ + +This is a collection of material that kernel developers should be familiar +with. + +.. toctree:: + :maxdepth: 1 + + changes + programming-language + coding-style + maintainer-pgp-guide + email-clients + applying-patches + backporting + adding-syscalls + volatile-considered-harmful + botching-up-ioctls + +Policy guides and developer statements +-------------------------------------- + +These are the rules that we try to live by in the kernel community (and +beyond). + +.. toctree:: + :maxdepth: 1 + + license-rules + code-of-conduct + code-of-conduct-interpretation + contribution-maturity-model + kernel-enforcement-statement + kernel-driver-statement + stable-api-nonsense + stable-kernel-rules + management-style + researcher-guidelines + generated-content + coding-assistants + conclave + +Dealing with bugs +----------------- + +Bugs are a fact of life; it is important that we handle them properly. The +documents below provide general advice about debugging and describe our +policies around the handling of a couple of special classes of bugs: +regressions and security problems. + +.. toctree:: + :maxdepth: 1 + + debugging/index + handling-regressions + security-bugs + threat-model + cve + embargoed-hardware-issues + +Maintainer information +---------------------- + +How to find the people who will accept your patches. + +.. toctree:: + :maxdepth: 1 + + maintainer-handbooks + maintainers + +Other material +-------------- + +Here are some other guides to the community that are of interest to most +developers: + +.. toctree:: + :maxdepth: 1 + + kernel-docs + deprecated -- cgit v1.3.1