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/sr.h | 77 +++++++++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 77 insertions(+) create mode 100644 drivers/scsi/sr.h (limited to 'drivers/scsi/sr.h') diff --git a/drivers/scsi/sr.h b/drivers/scsi/sr.h new file mode 100644 index 000000000..2d92f9cb6 --- /dev/null +++ b/drivers/scsi/sr.h @@ -0,0 +1,77 @@ +/* SPDX-License-Identifier: GPL-2.0 */ +/* + * sr.h by David Giller + * CD-ROM disk driver header file + * + * adapted from: + * sd.h Copyright (C) 1992 Drew Eckhardt + * SCSI disk driver header file by + * Drew Eckhardt + * + * + * + * Modified by Eric Youngdale eric@andante.org to + * add scatter-gather, multiple outstanding request, and other + * enhancements. + */ + +#ifndef _SR_H +#define _SR_H + +#include + +#define MAX_RETRIES 3 +#define SR_TIMEOUT (30 * HZ) + +struct scsi_device; + +/* The CDROM is fairly slow, so we need a little extra time */ +/* In fact, it is very slow if it has to spin up first */ +#define IOCTL_TIMEOUT 30*HZ + + +typedef struct scsi_cd { + unsigned capacity; /* size in blocks */ + struct scsi_device *device; + unsigned int vendor; /* vendor code, see sr_vendor.c */ + unsigned long ms_offset; /* for reading multisession-CD's */ + unsigned use:1; /* is this device still supportable */ + unsigned xa_flag:1; /* CD has XA sectors ? */ + unsigned readcd_known:1; /* drive supports READ_CD (0xbe) */ + unsigned readcd_cdda:1; /* reading audio data using READ_CD */ + unsigned media_present:1; /* media is present */ + + /* GET_EVENT spurious event handling, blk layer guarantees exclusion */ + int tur_mismatch; /* nr of get_event TUR mismatches */ + bool tur_changed:1; /* changed according to TUR */ + bool get_event_changed:1; /* changed according to GET_EVENT */ + bool ignore_get_event:1; /* GET_EVENT is unreliable, use TUR */ + + struct cdrom_device_info cdi; + struct mutex lock; + struct gendisk *disk; +} Scsi_CD; + +#define sr_printk(prefix, cd, fmt, a...) \ + sdev_prefix_printk(prefix, (cd)->device, (cd)->cdi.name, fmt, ##a) + +int sr_do_ioctl(Scsi_CD *, struct packet_command *); + +int sr_lock_door(struct cdrom_device_info *, int); +int sr_tray_move(struct cdrom_device_info *, int); +int sr_drive_status(struct cdrom_device_info *, int); +int sr_disk_status(struct cdrom_device_info *); +int sr_get_last_session(struct cdrom_device_info *, struct cdrom_multisession *); +int sr_get_mcn(struct cdrom_device_info *, struct cdrom_mcn *); +int sr_reset(struct cdrom_device_info *); +int sr_select_speed(struct cdrom_device_info *cdi, unsigned long speed); +int sr_audio_ioctl(struct cdrom_device_info *, unsigned int, void *); + +int sr_is_xa(Scsi_CD *); + +/* sr_vendor.c */ +void sr_vendor_init(Scsi_CD *); +int sr_cd_check(struct cdrom_device_info *); +int sr_set_blocklength(Scsi_CD *, int blocklength); + +#endif -- cgit v1.3.1