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 --- block/bio-integrity-auto.c | 127 +++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 127 insertions(+) create mode 100644 block/bio-integrity-auto.c (limited to 'block/bio-integrity-auto.c') diff --git a/block/bio-integrity-auto.c b/block/bio-integrity-auto.c new file mode 100644 index 000000000..9456dcffd --- /dev/null +++ b/block/bio-integrity-auto.c @@ -0,0 +1,127 @@ +// SPDX-License-Identifier: GPL-2.0 +/* + * Copyright (C) 2007, 2008, 2009 Oracle Corporation + * Written by: Martin K. Petersen + * + * Automatically generate and verify integrity data on PI capable devices if the + * bio submitter didn't provide PI itself. This ensures that kernel verifies + * data integrity even if the file system (or other user of the block device) is + * not aware of PI. + */ +#include +#include +#include +#include "blk.h" + +struct bio_integrity_data { + struct bio *bio; + struct bvec_iter saved_bio_iter; + struct work_struct work; + struct bio_integrity_payload bip; + struct bio_vec bvec; +}; + +static struct kmem_cache *bid_slab; +static mempool_t bid_pool; +static struct workqueue_struct *kintegrityd_wq; + +static void bio_integrity_finish(struct bio_integrity_data *bid) +{ + bid->bio->bi_integrity = NULL; + bid->bio->bi_opf &= ~REQ_INTEGRITY; + bio_integrity_free_buf(&bid->bip); + mempool_free(bid, &bid_pool); +} + +static void bio_integrity_verify_fn(struct work_struct *work) +{ + struct bio_integrity_data *bid = + container_of(work, struct bio_integrity_data, work); + struct bio *bio = bid->bio; + + bio->bi_status = bio_integrity_verify(bio, &bid->saved_bio_iter); + bio_integrity_finish(bid); + bio_endio(bio); +} + +/** + * __bio_integrity_endio - Integrity I/O completion function + * @bio: Protected bio + * + * Normally I/O completion is done in interrupt context. However, verifying I/O + * integrity is a time-consuming task which must be run in process context. + * + * This function postpones completion accordingly. + */ +bool __bio_integrity_endio(struct bio *bio) +{ + struct bio_integrity_payload *bip = bio_integrity(bio); + struct bio_integrity_data *bid = + container_of(bip, struct bio_integrity_data, bip); + + if (bio_op(bio) == REQ_OP_READ && !bio->bi_status && + (bip->bip_flags & BIP_CHECK_FLAGS)) { + INIT_WORK(&bid->work, bio_integrity_verify_fn); + queue_work(kintegrityd_wq, &bid->work); + return false; + } + + bio_integrity_finish(bid); + return true; +} + +/** + * bio_integrity_prep - Prepare bio for integrity I/O + * @bio: bio to prepare + * @action: preparation action needed (BI_ACT_*) + * + * Allocate the integrity payload. For writes, generate the integrity metadata + * and for reads, setup the completion handler to verify the metadata. + * + * This is used for bios that do not have user integrity payloads attached. + */ +void bio_integrity_prep(struct bio *bio, unsigned int action) +{ + struct bio_integrity_data *bid; + + bid = mempool_alloc(&bid_pool, GFP_NOIO); + bio_integrity_init(bio, &bid->bip, &bid->bvec, 1); + bid->bio = bio; + bid->bip.bip_flags |= BIP_BLOCK_INTEGRITY; + bio_integrity_alloc_buf(bio, GFP_NOIO, action & BI_ACT_ZERO); + if (action & BI_ACT_CHECK) + bio_integrity_setup_default(bio); + + /* Auto-generate integrity metadata if this is a write */ + if (bio_data_dir(bio) == WRITE && (bid->bip.bip_flags & BIP_CHECK_FLAGS)) + bio_integrity_generate(bio); + else + bid->saved_bio_iter = bio->bi_iter; +} +EXPORT_SYMBOL(bio_integrity_prep); + +void blk_flush_integrity(void) +{ + flush_workqueue(kintegrityd_wq); +} + +static int __init blk_integrity_auto_init(void) +{ + bid_slab = kmem_cache_create("bio_integrity_data", + sizeof(struct bio_integrity_data), 0, + SLAB_HWCACHE_ALIGN | SLAB_PANIC, NULL); + + if (mempool_init_slab_pool(&bid_pool, BIO_POOL_SIZE, bid_slab)) + panic("bio: can't create integrity pool\n"); + + /* + * kintegrityd won't block much but may burn a lot of CPU cycles. + * Make it highpri CPU intensive wq with max concurrency of 1. + */ + kintegrityd_wq = alloc_workqueue("kintegrityd", WQ_MEM_RECLAIM | + WQ_HIGHPRI | WQ_CPU_INTENSIVE | WQ_PERCPU, 1); + if (!kintegrityd_wq) + panic("Failed to create kintegrityd\n"); + return 0; +} +subsys_initcall(blk_integrity_auto_init); -- cgit v1.3.1