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 --- include/media/media-dev-allocator.h | 63 +++++++++++++++++++++++++++++++++++++ 1 file changed, 63 insertions(+) create mode 100644 include/media/media-dev-allocator.h (limited to 'include/media/media-dev-allocator.h') diff --git a/include/media/media-dev-allocator.h b/include/media/media-dev-allocator.h new file mode 100644 index 000000000..2ab54d426 --- /dev/null +++ b/include/media/media-dev-allocator.h @@ -0,0 +1,63 @@ +/* SPDX-License-Identifier: GPL-2.0+ */ +/* + * media-dev-allocator.h - Media Controller Device Allocator API + * + * Copyright (c) 2019 Shuah Khan + * + * Credits: Suggested by Laurent Pinchart + */ + +/* + * This file adds a global ref-counted Media Controller Device Instance API. + * A system wide global media device list is managed and each media device + * includes a kref count. The last put on the media device releases the media + * device instance. + */ + +#ifndef _MEDIA_DEV_ALLOCATOR_H +#define _MEDIA_DEV_ALLOCATOR_H + +struct usb_device; + +#if defined(CONFIG_MEDIA_CONTROLLER) && IS_ENABLED(CONFIG_USB) +/** + * media_device_usb_allocate() - Allocate and return struct &media device + * + * @udev: struct &usb_device pointer + * @module_name: should be filled with %KBUILD_MODNAME + * @owner: struct module pointer %THIS_MODULE for the driver. + * %THIS_MODULE is null for a built-in driver. + * It is safe even when %THIS_MODULE is null. + * + * This interface should be called to allocate a Media Device when multiple + * drivers share usb_device and the media device. This interface allocates + * &media_device structure and calls media_device_usb_init() to initialize + * it. + * + */ +struct media_device *media_device_usb_allocate(struct usb_device *udev, + const char *module_name, + struct module *owner); +/** + * media_device_delete() - Release media device. Calls kref_put(). + * + * @mdev: struct &media_device pointer + * @module_name: should be filled with %KBUILD_MODNAME + * @owner: struct module pointer %THIS_MODULE for the driver. + * %THIS_MODULE is null for a built-in driver. + * It is safe even when %THIS_MODULE is null. + * + * This interface should be called to put Media Device Instance kref. + */ +void media_device_delete(struct media_device *mdev, const char *module_name, + struct module *owner); +#else +static inline struct media_device *media_device_usb_allocate( + struct usb_device *udev, const char *module_name, + struct module *owner) + { return NULL; } +static inline void media_device_delete( + struct media_device *mdev, const char *module_name, + struct module *owner) { } +#endif /* CONFIG_MEDIA_CONTROLLER && CONFIG_USB */ +#endif /* _MEDIA_DEV_ALLOCATOR_H */ -- cgit v1.3.1