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/atm/common.h | 51 +++++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 51 insertions(+) create mode 100644 net/atm/common.h (limited to 'net/atm/common.h') diff --git a/net/atm/common.h b/net/atm/common.h new file mode 100644 index 000000000..11cb51dd7 --- /dev/null +++ b/net/atm/common.h @@ -0,0 +1,51 @@ +/* SPDX-License-Identifier: GPL-2.0 */ +/* net/atm/common.h - ATM sockets (common part for PVC and SVC) */ + +/* Written 1995-2000 by Werner Almesberger, EPFL LRC/ICA */ + + +#ifndef NET_ATM_COMMON_H +#define NET_ATM_COMMON_H + +#include +#include /* for poll_table */ + + +int vcc_create(struct net *net, struct socket *sock, int protocol, int family, int kern); +int vcc_release(struct socket *sock); +int vcc_connect(struct socket *sock, int itf, short vpi, int vci); +int vcc_recvmsg(struct socket *sock, struct msghdr *msg, size_t size, + int flags); +int vcc_sendmsg(struct socket *sock, struct msghdr *m, size_t total_len); +__poll_t vcc_poll(struct file *file, struct socket *sock, poll_table *wait); +int vcc_ioctl(struct socket *sock, unsigned int cmd, unsigned long arg); +int vcc_compat_ioctl(struct socket *sock, unsigned int cmd, unsigned long arg); +int vcc_setsockopt(struct socket *sock, int level, int optname, + sockptr_t optval, unsigned int optlen); +int vcc_getsockopt(struct socket *sock, int level, int optname, + sockopt_t *opt); +void vcc_process_recv_queue(struct atm_vcc *vcc); + +int atmpvc_init(void); +void atmpvc_exit(void); +int atm_sysfs_init(void); +void atm_sysfs_exit(void); + +#ifdef CONFIG_PROC_FS +int atm_proc_init(void); +void atm_proc_exit(void); +#else +static inline int atm_proc_init(void) +{ + return 0; +} + +static inline void atm_proc_exit(void) +{ + /* nothing */ +} +#endif /* CONFIG_PROC_FS */ + +void atm_dev_release_vccs(struct atm_dev *dev); + +#endif -- cgit v1.3.1