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/sysctl_net.c | 180 +++++++++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 180 insertions(+) create mode 100644 net/sysctl_net.c (limited to 'net/sysctl_net.c') diff --git a/net/sysctl_net.c b/net/sysctl_net.c new file mode 100644 index 000000000..e190a639e --- /dev/null +++ b/net/sysctl_net.c @@ -0,0 +1,180 @@ +// SPDX-License-Identifier: GPL-2.0-only +/* -*- linux-c -*- + * sysctl_net.c: sysctl interface to net subsystem. + * + * Begun April 1, 1996, Mike Shaver. + * Added /proc/sys/net directories for each protocol family. [MS] + * + * Revision 1.2 1996/05/08 20:24:40 shaver + * Added bits for NET_BRIDGE and the NET_IPV4_ARP stuff and + * NET_IPV4_IP_FORWARD. + * + * + */ + +#include +#include +#include +#include + +#include + +#ifdef CONFIG_INET +#include +#endif + +#ifdef CONFIG_NET +#include +#endif + +static struct ctl_table_set * +net_ctl_header_lookup(struct ctl_table_root *root) +{ + return ¤t->nsproxy->net_ns->sysctls; +} + +static int is_seen(struct ctl_table_set *set) +{ + return ¤t->nsproxy->net_ns->sysctls == set; +} + +/* Return standard mode bits for table entry. */ +static int net_ctl_permissions(struct ctl_table_header *head, + const struct ctl_table *table) +{ + struct net *net = container_of(head->set, struct net, sysctls); + + /* Allow network administrator to have same access as root. */ + if (ns_capable_noaudit(net->user_ns, CAP_NET_ADMIN)) { + int mode = (table->mode >> 6) & 7; + return (mode << 6) | (mode << 3) | mode; + } + + return table->mode; +} + +static void net_ctl_set_ownership(struct ctl_table_header *head, + kuid_t *uid, kgid_t *gid) +{ + struct net *net = container_of(head->set, struct net, sysctls); + kuid_t ns_root_uid; + kgid_t ns_root_gid; + + ns_root_uid = make_kuid(net->user_ns, 0); + if (uid_valid(ns_root_uid)) + *uid = ns_root_uid; + + ns_root_gid = make_kgid(net->user_ns, 0); + if (gid_valid(ns_root_gid)) + *gid = ns_root_gid; +} + +static struct ctl_table_root net_sysctl_root = { + .lookup = net_ctl_header_lookup, + .permissions = net_ctl_permissions, + .set_ownership = net_ctl_set_ownership, +}; + +static int __net_init sysctl_net_init(struct net *net) +{ + setup_sysctl_set(&net->sysctls, &net_sysctl_root, is_seen); + return 0; +} + +static void __net_exit sysctl_net_exit(struct net *net) +{ + retire_sysctl_set(&net->sysctls); +} + +static struct pernet_operations sysctl_pernet_ops = { + .init = sysctl_net_init, + .exit = sysctl_net_exit, +}; + +static struct ctl_table_header *net_header; +__init int net_sysctl_init(void) +{ + static struct ctl_table empty[1]; + int ret = -ENOMEM; + /* Avoid limitations in the sysctl implementation by + * registering "/proc/sys/net" as an empty directory not in a + * network namespace. + */ + net_header = register_sysctl_sz("net", empty, 0); + if (!net_header) + goto out; + ret = register_pernet_subsys(&sysctl_pernet_ops); + if (ret) + goto out1; +out: + return ret; +out1: + unregister_sysctl_table(net_header); + net_header = NULL; + goto out; +} + +/* Return error when sysctls for non-init netns are unsafe by verifying: + * 1) being read-only, or + * 2) having a data pointer which points outside of the global kernel/module + * data segment, and rather into the heap where a per-net object was + * allocated. + */ +static int ensure_safe_net_sysctl(struct net *net, const char *path, + const struct ctl_table *table, + size_t table_size) +{ + const struct ctl_table *ent; + + pr_debug("Registering net sysctl (net %p): %s\n", net, path); + ent = table; + for (size_t i = 0; i < table_size; ent++, i++) { + unsigned long addr; + const char *where; + + pr_debug(" procname=%s mode=%o proc_handler=%ps data=%p\n", + ent->procname, ent->mode, ent->proc_handler, ent->data); + + /* If it's not writable inside the netns, then it can't hurt. */ + if ((ent->mode & 0222) == 0) { + pr_debug(" Not writable by anyone\n"); + continue; + } + + /* Where does data point? */ + addr = (unsigned long)ent->data; + if (is_module_address(addr)) + where = "module"; + else if (is_kernel_core_data(addr)) + where = "kernel"; + else + continue; + + /* Warn on netns leak. */ + WARN(1, "sysctl %s/%s: data points to %s global data: %ps\n", + path, ent->procname, where, ent->data); + + return -EACCES; + } + + return 0; +} + +struct ctl_table_header *register_net_sysctl_sz(struct net *net, + const char *path, + const struct ctl_table *table, + size_t table_size) +{ + if (!net_eq(net, &init_net)) + if (ensure_safe_net_sysctl(net, path, table, table_size)) + return NULL; + + return __register_sysctl_table(&net->sysctls, path, table, table_size); +} +EXPORT_SYMBOL_GPL(register_net_sysctl_sz); + +void unregister_net_sysctl_table(struct ctl_table_header *header) +{ + unregister_sysctl_table(header); +} +EXPORT_SYMBOL_GPL(unregister_net_sysctl_table); -- cgit v1.3.1