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/net/scm.h | 114 ++++++++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 114 insertions(+) create mode 100644 include/net/scm.h (limited to 'include/net/scm.h') diff --git a/include/net/scm.h b/include/net/scm.h new file mode 100644 index 000000000..86ae6bc10 --- /dev/null +++ b/include/net/scm.h @@ -0,0 +1,114 @@ +/* SPDX-License-Identifier: GPL-2.0 */ +#ifndef __LINUX_NET_SCM_H +#define __LINUX_NET_SCM_H + +#include +#include +#include +#include +#include +#include +#include +#include +#include + +/* Well, we should have at least one descriptor open + * to accept passed FDs 8) + */ +#define SCM_MAX_FD 253 + +struct scm_creds { + u32 pid; + kuid_t uid; + kgid_t gid; +}; + +#ifdef CONFIG_UNIX +struct unix_edge; +#endif + +struct scm_fp_list { + short count; + short count_unix; + short max; +#ifdef CONFIG_UNIX + bool inflight; + bool dead; + struct list_head vertices; + struct unix_edge *edges; +#endif + struct user_struct *user; + struct file *fp[SCM_MAX_FD]; +}; + +struct scm_cookie { + struct pid *pid; /* Skb credentials */ + struct scm_fp_list *fp; /* Passed files */ + struct scm_creds creds; /* Skb credentials */ +#ifdef CONFIG_SECURITY_NETWORK + u32 secid; /* Passed security ID */ +#endif +}; + +void scm_detach_fds(struct msghdr *msg, struct scm_cookie *scm, bool notrunc); +void scm_detach_fds_compat(struct msghdr *msg, struct scm_cookie *scm, bool notrunc); +int __scm_send(struct socket *sock, struct msghdr *msg, struct scm_cookie *scm); +void __scm_destroy(struct scm_cookie *scm); +struct scm_fp_list *scm_fp_dup(struct scm_fp_list *fpl); + +#ifdef CONFIG_SECURITY_NETWORK +static __inline__ void unix_get_peersec_dgram(struct socket *sock, struct scm_cookie *scm) +{ + security_socket_getpeersec_dgram(sock, NULL, &scm->secid); +} +#else +static __inline__ void unix_get_peersec_dgram(struct socket *sock, struct scm_cookie *scm) +{ } +#endif /* CONFIG_SECURITY_NETWORK */ + +static __inline__ void scm_set_cred(struct scm_cookie *scm, + struct pid *pid, kuid_t uid, kgid_t gid) +{ + scm->pid = get_pid(pid); + scm->creds.pid = pid_vnr(pid); + scm->creds.uid = uid; + scm->creds.gid = gid; +} + +static __inline__ void scm_destroy_cred(struct scm_cookie *scm) +{ + put_pid(scm->pid); + scm->pid = NULL; +} + +static __inline__ void scm_destroy(struct scm_cookie *scm) +{ + scm_destroy_cred(scm); + if (scm->fp) + __scm_destroy(scm); +} + +static __inline__ int scm_send(struct socket *sock, struct msghdr *msg, + struct scm_cookie *scm, bool forcecreds) +{ + memset(scm, 0, sizeof(*scm)); + scm->creds.uid = INVALID_UID; + scm->creds.gid = INVALID_GID; + if (forcecreds) + scm_set_cred(scm, task_tgid(current), current_uid(), current_gid()); + unix_get_peersec_dgram(sock, scm); + if (msg->msg_controllen <= 0) + return 0; + return __scm_send(sock, msg, scm); +} + +void scm_recv(struct socket *sock, struct msghdr *msg, + struct scm_cookie *scm, int flags); +void scm_recv_unix(struct socket *sock, struct msghdr *msg, + struct scm_cookie *scm, int flags); + +int scm_recv_one_fd(struct file *f, int __user *ufd, unsigned int flags, + bool notrunc); + +#endif /* __LINUX_NET_SCM_H */ + -- cgit v1.3.1