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/queue.h | 104 +++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 104 insertions(+) create mode 100644 drivers/scsi/arm/queue.h (limited to 'drivers/scsi/arm/queue.h') diff --git a/drivers/scsi/arm/queue.h b/drivers/scsi/arm/queue.h new file mode 100644 index 000000000..cb51379dc --- /dev/null +++ b/drivers/scsi/arm/queue.h @@ -0,0 +1,104 @@ +/* SPDX-License-Identifier: GPL-2.0-only */ +/* + * linux/drivers/acorn/scsi/queue.h: queue handling + * + * Copyright (C) 1997 Russell King + */ +#ifndef QUEUE_H +#define QUEUE_H + +typedef struct { + struct list_head head; + struct list_head free; + spinlock_t queue_lock; + void *alloc; /* start of allocated mem */ +} Queue_t; + +/* + * Function: void queue_initialise (Queue_t *queue) + * Purpose : initialise a queue + * Params : queue - queue to initialise + */ +extern int queue_initialise (Queue_t *queue); + +/* + * Function: void queue_free (Queue_t *queue) + * Purpose : free a queue + * Params : queue - queue to free + */ +extern void queue_free (Queue_t *queue); + +/* + * Function: struct scsi_cmnd *queue_remove (queue) + * Purpose : removes first SCSI command from a queue + * Params : queue - queue to remove command from + * Returns : struct scsi_cmnd if successful (and a reference), or NULL if no command available + */ +extern struct scsi_cmnd *queue_remove (Queue_t *queue); + +/* + * Function: struct scsi_cmnd *queue_remove_exclude_ref (queue, exclude) + * Purpose : remove a SCSI command from a queue + * Params : queue - queue to remove command from + * exclude - array of busy LUNs + * Returns : struct scsi_cmnd if successful (and a reference), or NULL if no command available + */ +extern struct scsi_cmnd *queue_remove_exclude(Queue_t *queue, + unsigned long *exclude); + +#define queue_add_cmd_ordered(queue,SCpnt) \ + __queue_add(queue,SCpnt,(SCpnt)->cmnd[0] == REQUEST_SENSE) +#define queue_add_cmd_tail(queue,SCpnt) \ + __queue_add(queue,SCpnt,0) +/* + * Function: int __queue_add(Queue_t *queue, struct scsi_cmnd *SCpnt, int head) + * Purpose : Add a new command onto a queue + * Params : queue - destination queue + * SCpnt - command to add + * head - add command to head of queue + * Returns : 0 on error, !0 on success + */ +extern int __queue_add(Queue_t *queue, struct scsi_cmnd *SCpnt, int head); + +/* + * Function: struct scsi_cmnd *queue_remove_tgtluntag (queue, target, lun, tag) + * Purpose : remove a SCSI command from the queue for a specified target/lun/tag + * Params : queue - queue to remove command from + * target - target that we want + * lun - lun on device + * tag - tag on device + * Returns : struct scsi_cmnd if successful, or NULL if no command satisfies requirements + */ +extern struct scsi_cmnd *queue_remove_tgtluntag(Queue_t *queue, int target, + int lun, int tag); + +/* + * Function: queue_remove_all_target(queue, target) + * Purpose : remove all SCSI commands from the queue for a specified target + * Params : queue - queue to remove command from + * target - target device id + * Returns : nothing + */ +extern void queue_remove_all_target(Queue_t *queue, int target); + +/* + * Function: int queue_probetgtlun (queue, target, lun) + * Purpose : check to see if we have a command in the queue for the specified + * target/lun. + * Params : queue - queue to look in + * target - target we want to probe + * lun - lun on target + * Returns : 0 if not found, != 0 if found + */ +extern int queue_probetgtlun (Queue_t *queue, int target, int lun); + +/* + * Function: int queue_remove_cmd (Queue_t *queue, struct scsi_cmnd *SCpnt) + * Purpose : remove a specific command from the queues + * Params : queue - queue to look in + * SCpnt - command to find + * Returns : 0 if not found + */ +int queue_remove_cmd(Queue_t *queue, struct scsi_cmnd *SCpnt); + +#endif /* QUEUE_H */ -- cgit v1.3.1