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/scsi/arm/msgqueue.c | 168 ++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 168 insertions(+) create mode 100644 drivers/scsi/arm/msgqueue.c (limited to 'drivers/scsi/arm/msgqueue.c') diff --git a/drivers/scsi/arm/msgqueue.c b/drivers/scsi/arm/msgqueue.c new file mode 100644 index 000000000..581158313 --- /dev/null +++ b/drivers/scsi/arm/msgqueue.c @@ -0,0 +1,168 @@ +// SPDX-License-Identifier: GPL-2.0-only +/* + * linux/drivers/acorn/scsi/msgqueue.c + * + * Copyright (C) 1997-1998 Russell King + * + * message queue handling + */ +#include +#include +#include +#include + +#include "msgqueue.h" + +/* + * Function: struct msgqueue_entry *mqe_alloc(MsgQueue_t *msgq) + * Purpose : Allocate a message queue entry + * Params : msgq - message queue to claim entry for + * Returns : message queue entry or NULL. + */ +static struct msgqueue_entry *mqe_alloc(MsgQueue_t *msgq) +{ + struct msgqueue_entry *mq; + + if ((mq = msgq->free) != NULL) + msgq->free = mq->next; + + return mq; +} + +/* + * Function: void mqe_free(MsgQueue_t *msgq, struct msgqueue_entry *mq) + * Purpose : free a message queue entry + * Params : msgq - message queue to free entry from + * mq - message queue entry to free + */ +static void mqe_free(MsgQueue_t *msgq, struct msgqueue_entry *mq) +{ + if (mq) { + mq->next = msgq->free; + msgq->free = mq; + } +} + +/* + * Function: void msgqueue_initialise(MsgQueue_t *msgq) + * Purpose : initialise a message queue + * Params : msgq - queue to initialise + */ +void msgqueue_initialise(MsgQueue_t *msgq) +{ + int i; + + msgq->qe = NULL; + msgq->free = &msgq->entries[0]; + + for (i = 0; i < NR_MESSAGES; i++) + msgq->entries[i].next = &msgq->entries[i + 1]; + + msgq->entries[NR_MESSAGES - 1].next = NULL; +} + + +/* + * Function: void msgqueue_free(MsgQueue_t *msgq) + * Purpose : free a queue + * Params : msgq - queue to free + */ +void msgqueue_free(MsgQueue_t *msgq) +{ +} + +/* + * Function: int msgqueue_msglength(MsgQueue_t *msgq) + * Purpose : calculate the total length of all messages on the message queue + * Params : msgq - queue to examine + * Returns : number of bytes of messages in queue + */ +int msgqueue_msglength(MsgQueue_t *msgq) +{ + struct msgqueue_entry *mq = msgq->qe; + int length = 0; + + for (mq = msgq->qe; mq; mq = mq->next) + length += mq->msg.length; + + return length; +} + +/* + * Function: struct message *msgqueue_getmsg(MsgQueue_t *msgq, int msgno) + * Purpose : return a message + * Params : msgq - queue to obtain message from + * : msgno - message number + * Returns : pointer to message string, or NULL + */ +struct message *msgqueue_getmsg(MsgQueue_t *msgq, int msgno) +{ + struct msgqueue_entry *mq; + + for (mq = msgq->qe; mq && msgno; mq = mq->next, msgno--); + + return mq ? &mq->msg : NULL; +} + +/* + * Function: int msgqueue_addmsg(MsgQueue_t *msgq, int length, ...) + * Purpose : add a message onto a message queue + * Params : msgq - queue to add message on + * length - length of message + * ... - message bytes + * Returns : != 0 if successful + */ +int msgqueue_addmsg(MsgQueue_t *msgq, int length, ...) +{ + struct msgqueue_entry *mq = mqe_alloc(msgq); + va_list ap; + + if (mq) { + struct msgqueue_entry **mqp; + int i; + + va_start(ap, length); + for (i = 0; i < length; i++) + mq->msg.msg[i] = va_arg(ap, unsigned int); + va_end(ap); + + mq->msg.length = length; + mq->msg.fifo = 0; + mq->next = NULL; + + mqp = &msgq->qe; + while (*mqp) + mqp = &(*mqp)->next; + + *mqp = mq; + } + + return mq != NULL; +} + +/* + * Function: void msgqueue_flush(MsgQueue_t *msgq) + * Purpose : flush all messages from message queue + * Params : msgq - queue to flush + */ +void msgqueue_flush(MsgQueue_t *msgq) +{ + struct msgqueue_entry *mq, *mqnext; + + for (mq = msgq->qe; mq; mq = mqnext) { + mqnext = mq->next; + mqe_free(msgq, mq); + } + msgq->qe = NULL; +} + +EXPORT_SYMBOL(msgqueue_initialise); +EXPORT_SYMBOL(msgqueue_free); +EXPORT_SYMBOL(msgqueue_msglength); +EXPORT_SYMBOL(msgqueue_getmsg); +EXPORT_SYMBOL(msgqueue_addmsg); +EXPORT_SYMBOL(msgqueue_flush); + +MODULE_AUTHOR("Russell King"); +MODULE_DESCRIPTION("SCSI message queue handling"); +MODULE_LICENSE("GPL"); -- cgit v1.3.1