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/mtd/devices/mtdram.c | 187 +++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 187 insertions(+) create mode 100644 drivers/mtd/devices/mtdram.c (limited to 'drivers/mtd/devices/mtdram.c') diff --git a/drivers/mtd/devices/mtdram.c b/drivers/mtd/devices/mtdram.c new file mode 100644 index 000000000..3fff3cdd9 --- /dev/null +++ b/drivers/mtd/devices/mtdram.c @@ -0,0 +1,187 @@ +/* + * mtdram - a test mtd device + * Author: Alexander Larsson + * + * Copyright (c) 1999 Alexander Larsson + * Copyright (c) 2005 Joern Engel + * + * This code is GPL + * + */ + +#include +#include +#include +#include +#include +#include +#include +#include + +static unsigned long total_size = CONFIG_MTDRAM_TOTAL_SIZE; +static unsigned long erase_size = CONFIG_MTDRAM_ERASE_SIZE; +static unsigned long writebuf_size = 64; +#define MTDRAM_TOTAL_SIZE (total_size * 1024) +#define MTDRAM_ERASE_SIZE (erase_size * 1024) + +module_param(total_size, ulong, 0); +MODULE_PARM_DESC(total_size, "Total device size in KiB"); +module_param(erase_size, ulong, 0); +MODULE_PARM_DESC(erase_size, "Device erase block size in KiB"); +module_param(writebuf_size, ulong, 0); +MODULE_PARM_DESC(writebuf_size, "Device write buf size in Bytes (Default: 64)"); + +// We could store these in the mtd structure, but we only support 1 device.. +static struct mtd_info *mtd_info; + +static int check_offs_len(struct mtd_info *mtd, loff_t ofs, uint64_t len) +{ + int ret = 0; + + /* Start address must align on block boundary */ + if (mtd_mod_by_eb(ofs, mtd)) { + pr_debug("%s: unaligned address\n", __func__); + ret = -EINVAL; + } + + /* Length must align on block boundary */ + if (mtd_mod_by_eb(len, mtd)) { + pr_debug("%s: length not block aligned\n", __func__); + ret = -EINVAL; + } + + return ret; +} + +static int ram_erase(struct mtd_info *mtd, struct erase_info *instr) +{ + if (check_offs_len(mtd, instr->addr, instr->len)) + return -EINVAL; + memset((char *)mtd->priv + instr->addr, 0xff, instr->len); + + return 0; +} + +static int ram_point(struct mtd_info *mtd, loff_t from, size_t len, + size_t *retlen, void **virt, resource_size_t *phys) +{ + *virt = mtd->priv + from; + *retlen = len; + + if (phys) { + /* limit retlen to the number of contiguous physical pages */ + unsigned long page_ofs = offset_in_page(*virt); + void *addr = *virt - page_ofs; + unsigned long pfn1, pfn0 = vmalloc_to_pfn(addr); + + *phys = __pfn_to_phys(pfn0) + page_ofs; + len += page_ofs; + while (len > PAGE_SIZE) { + len -= PAGE_SIZE; + addr += PAGE_SIZE; + pfn0++; + pfn1 = vmalloc_to_pfn(addr); + if (pfn1 != pfn0) { + *retlen = addr - *virt; + break; + } + } + } + + return 0; +} + +static int ram_unpoint(struct mtd_info *mtd, loff_t from, size_t len) +{ + return 0; +} + +static int ram_read(struct mtd_info *mtd, loff_t from, size_t len, + size_t *retlen, u_char *buf) +{ + memcpy(buf, mtd->priv + from, len); + *retlen = len; + return 0; +} + +static int ram_write(struct mtd_info *mtd, loff_t to, size_t len, + size_t *retlen, const u_char *buf) +{ + memcpy((char *)mtd->priv + to, buf, len); + *retlen = len; + return 0; +} + +static void __exit cleanup_mtdram(void) +{ + if (mtd_info) { + mtd_device_unregister(mtd_info); + vfree(mtd_info->priv); + kfree(mtd_info); + } +} + +int mtdram_init_device(struct mtd_info *mtd, void *mapped_address, + unsigned long size, const char *name) +{ + memset(mtd, 0, sizeof(*mtd)); + + /* Setup the MTD structure */ + mtd->name = name; + mtd->type = MTD_RAM; + mtd->flags = MTD_CAP_RAM; + mtd->size = size; + mtd->writesize = 1; + mtd->writebufsize = writebuf_size; + mtd->erasesize = MTDRAM_ERASE_SIZE; + mtd->priv = mapped_address; + + mtd->owner = THIS_MODULE; + mtd->_erase = ram_erase; + mtd->_point = ram_point; + mtd->_unpoint = ram_unpoint; + mtd->_read = ram_read; + mtd->_write = ram_write; + + if (mtd_device_register(mtd, NULL, 0)) + return -EIO; + + return 0; +} + +static int __init init_mtdram(void) +{ + void *addr; + int err; + + if (!total_size) + return -EINVAL; + + /* Allocate some memory */ + mtd_info = kmalloc_obj(struct mtd_info); + if (!mtd_info) + return -ENOMEM; + + addr = vmalloc(MTDRAM_TOTAL_SIZE); + if (!addr) { + kfree(mtd_info); + mtd_info = NULL; + return -ENOMEM; + } + err = mtdram_init_device(mtd_info, addr, MTDRAM_TOTAL_SIZE, "mtdram test device"); + if (err) { + vfree(addr); + kfree(mtd_info); + mtd_info = NULL; + return err; + } + memset(mtd_info->priv, 0xff, MTDRAM_TOTAL_SIZE); + return err; +} + +module_init(init_mtdram); +module_exit(cleanup_mtdram); + +MODULE_LICENSE("GPL"); +MODULE_AUTHOR("Alexander Larsson "); +MODULE_DESCRIPTION("Simulated MTD driver for testing"); -- cgit v1.3.1