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 --- mm/memtest.c | 139 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 139 insertions(+) create mode 100644 mm/memtest.c (limited to 'mm/memtest.c') diff --git a/mm/memtest.c b/mm/memtest.c new file mode 100644 index 000000000..520d41534 --- /dev/null +++ b/mm/memtest.c @@ -0,0 +1,139 @@ +// SPDX-License-Identifier: GPL-2.0 +#include +#include +#include +#include +#include + +static bool early_memtest_done; +static phys_addr_t early_memtest_bad_size; + +static u64 patterns[] __initdata = { + /* The first entry has to be 0 to leave memtest with zeroed memory */ + 0, + 0xffffffffffffffffULL, + 0x5555555555555555ULL, + 0xaaaaaaaaaaaaaaaaULL, + 0x1111111111111111ULL, + 0x2222222222222222ULL, + 0x4444444444444444ULL, + 0x8888888888888888ULL, + 0x3333333333333333ULL, + 0x6666666666666666ULL, + 0x9999999999999999ULL, + 0xccccccccccccccccULL, + 0x7777777777777777ULL, + 0xbbbbbbbbbbbbbbbbULL, + 0xddddddddddddddddULL, + 0xeeeeeeeeeeeeeeeeULL, + 0x7a6c7258554e494cULL, /* yeah ;-) */ +}; + +static void __init reserve_bad_mem(u64 pattern, phys_addr_t start_bad, phys_addr_t end_bad) +{ + pr_info(" %016llx bad mem addr %pa - %pa reserved\n", + cpu_to_be64(pattern), &start_bad, &end_bad); + memblock_reserve(start_bad, end_bad - start_bad); + early_memtest_bad_size += (end_bad - start_bad); +} + +static void __init memtest(u64 pattern, phys_addr_t start_phys, phys_addr_t size) +{ + u64 *p, *start, *end; + phys_addr_t start_bad, last_bad; + phys_addr_t start_phys_aligned; + const size_t incr = sizeof(pattern); + + start_phys_aligned = ALIGN(start_phys, incr); + start = __va(start_phys_aligned); + end = start + (size - (start_phys_aligned - start_phys)) / incr; + start_bad = 0; + last_bad = 0; + + VM_WARN_ON_ONCE(size < start_phys_aligned - start_phys); + + for (p = start; p < end; p++) + WRITE_ONCE(*p, pattern); + + for (p = start; p < end; p++, start_phys_aligned += incr) { + if (READ_ONCE(*p) == pattern) + continue; + if (start_phys_aligned == last_bad + incr) { + last_bad += incr; + continue; + } + if (start_bad) + reserve_bad_mem(pattern, start_bad, last_bad + incr); + start_bad = last_bad = start_phys_aligned; + } + if (start_bad) + reserve_bad_mem(pattern, start_bad, last_bad + incr); + + early_memtest_done = true; +} + +static void __init do_one_pass(u64 pattern, phys_addr_t start, phys_addr_t end) +{ + u64 i; + phys_addr_t this_start, this_end; + + for_each_free_mem_range(i, NUMA_NO_NODE, MEMBLOCK_NONE, &this_start, + &this_end, NULL) { + this_start = clamp(this_start, start, end); + this_end = clamp(this_end, start, end); + if (this_start < this_end) { + pr_info(" %pa - %pa pattern %016llx\n", + &this_start, &this_end, cpu_to_be64(pattern)); + memtest(pattern, this_start, this_end - this_start); + } + } +} + +/* default is disabled */ +static unsigned int memtest_pattern __initdata; + +static int __init parse_memtest(char *arg) +{ + int ret = 0; + + if (arg) + ret = kstrtouint(arg, 0, &memtest_pattern); + else + memtest_pattern = ARRAY_SIZE(patterns); + + return ret; +} + +early_param("memtest", parse_memtest); + +void __init early_memtest(phys_addr_t start, phys_addr_t end) +{ + unsigned int i; + unsigned int idx = 0; + + if (!memtest_pattern) + return; + + pr_info("early_memtest: # of tests: %u\n", memtest_pattern); + for (i = memtest_pattern-1; i < UINT_MAX; --i) { + idx = i % ARRAY_SIZE(patterns); + do_one_pass(patterns[idx], start, end); + } +} + +void memtest_report_meminfo(struct seq_file *m) +{ + unsigned long early_memtest_bad_size_kb; + + if (!IS_ENABLED(CONFIG_PROC_FS)) + return; + + if (!early_memtest_done) + return; + + early_memtest_bad_size_kb = early_memtest_bad_size >> 10; + if (early_memtest_bad_size && !early_memtest_bad_size_kb) + early_memtest_bad_size_kb = 1; + /* When 0 is reported, it means there actually was a successful test */ + seq_printf(m, "EarlyMemtestBad: %5lu kB\n", early_memtest_bad_size_kb); +} -- cgit v1.3.1