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 --- net/sctp/objcnt.c | 105 ++++++++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 105 insertions(+) create mode 100644 net/sctp/objcnt.c (limited to 'net/sctp/objcnt.c') diff --git a/net/sctp/objcnt.c b/net/sctp/objcnt.c new file mode 100644 index 000000000..0400c964e --- /dev/null +++ b/net/sctp/objcnt.c @@ -0,0 +1,105 @@ +// SPDX-License-Identifier: GPL-2.0-or-later +/* SCTP kernel implementation + * (C) Copyright IBM Corp. 2001, 2004 + * + * This file is part of the SCTP kernel implementation + * + * Support for memory object debugging. This allows one to monitor the + * object allocations/deallocations for types instrumented for this + * via the proc fs. + * + * Please send any bug reports or fixes you make to the + * email address(es): + * lksctp developers + * + * Written or modified by: + * Jon Grimm + */ + +#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt + +#include +#include + +/* + * Global counters to count raw object allocation counts. + * To add new counters, choose a unique suffix for the variable + * name as the helper macros key off this suffix to make + * life easier for the programmer. + */ + +SCTP_DBG_OBJCNT(sock); +SCTP_DBG_OBJCNT(ep); +SCTP_DBG_OBJCNT(transport); +SCTP_DBG_OBJCNT(assoc); +SCTP_DBG_OBJCNT(bind_addr); +SCTP_DBG_OBJCNT(bind_bucket); +SCTP_DBG_OBJCNT(chunk); +SCTP_DBG_OBJCNT(addr); +SCTP_DBG_OBJCNT(datamsg); +SCTP_DBG_OBJCNT(keys); + +/* An array to make it easy to pretty print the debug information + * to the proc fs. + */ +static struct sctp_dbg_objcnt_entry sctp_dbg_objcnt[] = { + SCTP_DBG_OBJCNT_ENTRY(sock), + SCTP_DBG_OBJCNT_ENTRY(ep), + SCTP_DBG_OBJCNT_ENTRY(assoc), + SCTP_DBG_OBJCNT_ENTRY(transport), + SCTP_DBG_OBJCNT_ENTRY(chunk), + SCTP_DBG_OBJCNT_ENTRY(bind_addr), + SCTP_DBG_OBJCNT_ENTRY(bind_bucket), + SCTP_DBG_OBJCNT_ENTRY(addr), + SCTP_DBG_OBJCNT_ENTRY(datamsg), + SCTP_DBG_OBJCNT_ENTRY(keys), +}; + +/* Callback from procfs to read out objcount information. + * Walk through the entries in the sctp_dbg_objcnt array, dumping + * the raw object counts for each monitored type. + */ +static int sctp_objcnt_seq_show(struct seq_file *seq, void *v) +{ + int i; + + i = (int)*(loff_t *)v; + seq_setwidth(seq, 127); + seq_printf(seq, "%s: %d", sctp_dbg_objcnt[i].label, + atomic_read(sctp_dbg_objcnt[i].counter)); + seq_pad(seq, '\n'); + return 0; +} + +static void *sctp_objcnt_seq_start(struct seq_file *seq, loff_t *pos) +{ + return (*pos >= ARRAY_SIZE(sctp_dbg_objcnt)) ? NULL : (void *)pos; +} + +static void sctp_objcnt_seq_stop(struct seq_file *seq, void *v) +{ +} + +static void *sctp_objcnt_seq_next(struct seq_file *seq, void *v, loff_t *pos) +{ + ++*pos; + return (*pos >= ARRAY_SIZE(sctp_dbg_objcnt)) ? NULL : (void *)pos; +} + +static const struct seq_operations sctp_objcnt_seq_ops = { + .start = sctp_objcnt_seq_start, + .next = sctp_objcnt_seq_next, + .stop = sctp_objcnt_seq_stop, + .show = sctp_objcnt_seq_show, +}; + +/* Initialize the objcount in the proc filesystem. */ +void sctp_dbg_objcnt_init(struct net *net) +{ + struct proc_dir_entry *ent; + + ent = proc_create_seq("sctp_dbg_objcnt", 0, + net->sctp.proc_net_sctp, &sctp_objcnt_seq_ops); + if (!ent) + pr_warn("sctp_dbg_objcnt: Unable to create /proc entry.\n"); +} -- cgit v1.3.1