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 --- arch/powerpc/boot/hack-coff.c | 80 +++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 80 insertions(+) create mode 100644 arch/powerpc/boot/hack-coff.c (limited to 'arch/powerpc/boot/hack-coff.c') diff --git a/arch/powerpc/boot/hack-coff.c b/arch/powerpc/boot/hack-coff.c new file mode 100644 index 000000000..6bf0c9430 --- /dev/null +++ b/arch/powerpc/boot/hack-coff.c @@ -0,0 +1,80 @@ +// SPDX-License-Identifier: GPL-2.0-or-later +/* + * hack-coff.c - hack the header of an xcoff file to fill in + * a few fields needed by the Open Firmware xcoff loader on + * Power Macs but not initialized by objcopy. + * + * Copyright (C) Paul Mackerras 1997. + */ +#include +#include +#include +#include +#include +#include "rs6000.h" + +#define AOUT_MAGIC 0x010b + +#define get_16be(x) ((((unsigned char *)(x))[0] << 8) \ + + ((unsigned char *)(x))[1]) +#define put_16be(x, v) (((unsigned char *)(x))[0] = (v) >> 8, \ + ((unsigned char *)(x))[1] = (v) & 0xff) +#define get_32be(x) ((((unsigned char *)(x))[0] << 24) \ + + (((unsigned char *)(x))[1] << 16) \ + + (((unsigned char *)(x))[2] << 8) \ + + ((unsigned char *)(x))[3]) + +int +main(int ac, char **av) +{ + int fd; + int i, nsect; + int aoutsz; + struct external_filehdr fhdr; + struct aouthdr aout; + struct external_scnhdr shdr; + + if (ac != 2) { + fprintf(stderr, "Usage: hack-coff coff-file\n"); + exit(1); + } + if ((fd = open(av[1], 2)) == -1) { + perror(av[2]); + exit(1); + } + if (read(fd, &fhdr, sizeof(fhdr)) != sizeof(fhdr)) + goto readerr; + i = get_16be(fhdr.f_magic); + if (i != U802TOCMAGIC && i != U802WRMAGIC && i != U802ROMAGIC) { + fprintf(stderr, "%s: not an xcoff file\n", av[1]); + exit(1); + } + aoutsz = get_16be(fhdr.f_opthdr); + if (read(fd, &aout, aoutsz) != aoutsz) + goto readerr; + nsect = get_16be(fhdr.f_nscns); + for (i = 0; i < nsect; ++i) { + if (read(fd, &shdr, sizeof(shdr)) != sizeof(shdr)) + goto readerr; + if (strcmp(shdr.s_name, ".text") == 0) { + put_16be(aout.o_snentry, i+1); + put_16be(aout.o_sntext, i+1); + } else if (strcmp(shdr.s_name, ".data") == 0) { + put_16be(aout.o_sndata, i+1); + } else if (strcmp(shdr.s_name, ".bss") == 0) { + put_16be(aout.o_snbss, i+1); + } + } + put_16be(aout.magic, AOUT_MAGIC); + if (lseek(fd, (long) sizeof(struct external_filehdr), 0) == -1 + || write(fd, &aout, aoutsz) != aoutsz) { + fprintf(stderr, "%s: write error\n", av[1]); + exit(1); + } + close(fd); + exit(0); + +readerr: + fprintf(stderr, "%s: read error or file too short\n", av[1]); + exit(1); +} -- cgit v1.3.1