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 --- drivers/md/bcache/features.c | 75 ++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 75 insertions(+) create mode 100644 drivers/md/bcache/features.c (limited to 'drivers/md/bcache/features.c') diff --git a/drivers/md/bcache/features.c b/drivers/md/bcache/features.c new file mode 100644 index 000000000..634922c56 --- /dev/null +++ b/drivers/md/bcache/features.c @@ -0,0 +1,75 @@ +// SPDX-License-Identifier: GPL-2.0 +/* + * Feature set bits and string conversion. + * Inspired by ext4's features compat/incompat/ro_compat related code. + * + * Copyright 2020 Coly Li + * + */ +#include "bcache_ondisk.h" +#include "bcache.h" +#include "features.h" + +struct feature { + int compat; + unsigned int mask; + const char *string; +}; + +static struct feature feature_list[] = { + {BCH_FEATURE_INCOMPAT, BCH_FEATURE_INCOMPAT_LOG_LARGE_BUCKET_SIZE, + "large_bucket"}, + {0, 0, NULL }, +}; + +#define compose_feature_string(type) \ +({ \ + struct feature *f; \ + bool first = true; \ + \ + for (f = &feature_list[0]; f->compat != 0; f++) { \ + if (f->compat != BCH_FEATURE_ ## type) \ + continue; \ + if (BCH_HAS_ ## type ## _FEATURE(&c->cache->sb, f->mask)) { \ + if (first) { \ + out += snprintf(out, buf + size - out, \ + "["); \ + } else { \ + out += snprintf(out, buf + size - out, \ + " ["); \ + } \ + } else if (!first) { \ + out += snprintf(out, buf + size - out, " "); \ + } \ + \ + out += snprintf(out, buf + size - out, "%s", f->string);\ + \ + if (BCH_HAS_ ## type ## _FEATURE(&c->cache->sb, f->mask)) \ + out += snprintf(out, buf + size - out, "]"); \ + \ + first = false; \ + } \ + if (!first) \ + out += snprintf(out, buf + size - out, "\n"); \ +}) + +int bch_print_cache_set_feature_compat(struct cache_set *c, char *buf, int size) +{ + char *out = buf; + compose_feature_string(COMPAT); + return out - buf; +} + +int bch_print_cache_set_feature_ro_compat(struct cache_set *c, char *buf, int size) +{ + char *out = buf; + compose_feature_string(RO_COMPAT); + return out - buf; +} + +int bch_print_cache_set_feature_incompat(struct cache_set *c, char *buf, int size) +{ + char *out = buf; + compose_feature_string(INCOMPAT); + return out - buf; +} -- cgit v1.3.1