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 --- fs/jfs/jfs_debug.c | 80 ++++++++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 80 insertions(+) create mode 100644 fs/jfs/jfs_debug.c (limited to 'fs/jfs/jfs_debug.c') diff --git a/fs/jfs/jfs_debug.c b/fs/jfs/jfs_debug.c new file mode 100644 index 000000000..44b62b3c3 --- /dev/null +++ b/fs/jfs/jfs_debug.c @@ -0,0 +1,80 @@ +// SPDX-License-Identifier: GPL-2.0-or-later +/* + * Copyright (C) International Business Machines Corp., 2000-2004 + * Portions Copyright (C) Christoph Hellwig, 2001-2002 + */ + +#include +#include +#include +#include +#include +#include +#include "jfs_incore.h" +#include "jfs_filsys.h" +#include "jfs_debug.h" + +#ifdef PROC_FS_JFS /* see jfs_debug.h */ + +#ifdef CONFIG_JFS_DEBUG +static int jfs_loglevel_proc_show(struct seq_file *m, void *v) +{ + seq_printf(m, "%d\n", jfsloglevel); + return 0; +} + +static int jfs_loglevel_proc_open(struct inode *inode, struct file *file) +{ + return single_open(file, jfs_loglevel_proc_show, NULL); +} + +static ssize_t jfs_loglevel_proc_write(struct file *file, + const char __user *buffer, size_t count, loff_t *ppos) +{ + char c; + + if (get_user(c, buffer)) + return -EFAULT; + + /* yes, I know this is an ASCIIism. --hch */ + if (c < '0' || c > '9') + return -EINVAL; + jfsloglevel = c - '0'; + return count; +} + +static const struct proc_ops jfs_loglevel_proc_ops = { + .proc_open = jfs_loglevel_proc_open, + .proc_read = seq_read, + .proc_lseek = seq_lseek, + .proc_release = single_release, + .proc_write = jfs_loglevel_proc_write, +}; +#endif + +void jfs_proc_init(void) +{ + struct proc_dir_entry *base; + + base = proc_mkdir("fs/jfs", NULL); + if (!base) + return; + +#ifdef CONFIG_JFS_STATISTICS + proc_create_single("lmstats", 0, base, jfs_lmstats_proc_show); + proc_create_single("txstats", 0, base, jfs_txstats_proc_show); + proc_create_single("xtstat", 0, base, jfs_xtstat_proc_show); + proc_create_single("mpstat", 0, base, jfs_mpstat_proc_show); +#endif +#ifdef CONFIG_JFS_DEBUG + proc_create_single("TxAnchor", 0, base, jfs_txanchor_proc_show); + proc_create("loglevel", 0, base, &jfs_loglevel_proc_ops); +#endif +} + +void jfs_proc_clean(void) +{ + remove_proc_subtree("fs/jfs", NULL); +} + +#endif /* PROC_FS_JFS */ -- cgit v1.3.1