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/llc/llc_input.c | 224 ++++++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 224 insertions(+) create mode 100644 net/llc/llc_input.c (limited to 'net/llc/llc_input.c') diff --git a/net/llc/llc_input.c b/net/llc/llc_input.c new file mode 100644 index 000000000..8eb3d73c3 --- /dev/null +++ b/net/llc/llc_input.c @@ -0,0 +1,224 @@ +// SPDX-License-Identifier: GPL-2.0 +/* + * llc_input.c - Minimal input path for LLC + * + * Copyright (c) 1997 by Procom Technology, Inc. + * 2001-2003 by Arnaldo Carvalho de Melo + */ +#include +#include +#include +#include +#include +#include +#include + +#if 0 +#define dprintk(args...) printk(KERN_DEBUG args) +#else +#define dprintk(args...) +#endif + +/* + * Packet handler for the station, registerable because in the minimal + * LLC core that is taking shape only the very minimal subset of LLC that + * is needed for things like IPX, Appletalk, etc will stay, with all the + * rest in the llc1 and llc2 modules. + */ +static void (*llc_station_handler)(struct sk_buff *skb); + +/* + * Packet handlers for LLC_DEST_SAP and LLC_DEST_CONN. + */ +static void (*llc_type_handlers[2])(struct llc_sap *sap, + struct sk_buff *skb); + +void llc_add_pack(int type, void (*handler)(struct llc_sap *sap, + struct sk_buff *skb)) +{ + smp_wmb(); /* ensure initialisation is complete before it's called */ + if (type == LLC_DEST_SAP || type == LLC_DEST_CONN) + llc_type_handlers[type - 1] = handler; +} + +void llc_remove_pack(int type) +{ + if (type == LLC_DEST_SAP || type == LLC_DEST_CONN) + llc_type_handlers[type - 1] = NULL; + synchronize_net(); +} + +void llc_set_station_handler(void (*handler)(struct sk_buff *skb)) +{ + /* Ensure initialisation is complete before it's called */ + if (handler) + smp_wmb(); + + llc_station_handler = handler; + + if (!handler) + synchronize_net(); +} + +/** + * llc_pdu_type - returns which LLC component must handle for PDU + * @skb: input skb + * + * This function returns which LLC component must handle this PDU. + */ +static __inline__ int llc_pdu_type(struct sk_buff *skb) +{ + int type = LLC_DEST_CONN; /* I-PDU or S-PDU type */ + struct llc_pdu_sn *pdu = llc_pdu_sn_hdr(skb); + + if ((pdu->ctrl_1 & LLC_PDU_TYPE_MASK) != LLC_PDU_TYPE_U) + goto out; + switch (LLC_U_PDU_CMD(pdu)) { + case LLC_1_PDU_CMD_XID: + case LLC_1_PDU_CMD_UI: + case LLC_1_PDU_CMD_TEST: + type = LLC_DEST_SAP; + break; + case LLC_2_PDU_CMD_SABME: + case LLC_2_PDU_CMD_DISC: + case LLC_2_PDU_RSP_UA: + case LLC_2_PDU_RSP_DM: + case LLC_2_PDU_RSP_FRMR: + break; + default: + type = LLC_DEST_INVALID; + break; + } +out: + return type; +} + +/** + * llc_fixup_skb - initializes skb pointers + * @skb: This argument points to incoming skb + * + * Initializes internal skb pointer to start of network layer by deriving + * length of LLC header; finds length of LLC control field in LLC header + * by looking at the two lowest-order bits of the first control field + * byte; field is either 3 or 4 bytes long. + */ +static inline int llc_fixup_skb(struct sk_buff *skb) +{ + u8 llc_len = 2; + struct llc_pdu_un *pdu; + + if (unlikely(!pskb_may_pull(skb, sizeof(*pdu)))) + return 0; + + pdu = (struct llc_pdu_un *)skb->data; + if ((pdu->ctrl_1 & LLC_PDU_TYPE_MASK) == LLC_PDU_TYPE_U) + llc_len = 1; + llc_len += 2; + + if (unlikely(!pskb_may_pull(skb, llc_len))) + return 0; + + skb_pull(skb, llc_len); + skb_reset_transport_header(skb); + if (skb->protocol == htons(ETH_P_802_2)) { + __be16 pdulen; + s32 data_size; + + if (skb->mac_len < ETH_HLEN) + return 0; + + pdulen = eth_hdr(skb)->h_proto; + data_size = ntohs(pdulen) - llc_len; + + if (data_size < 0 || + !pskb_may_pull(skb, data_size)) + return 0; + if (unlikely(pskb_trim_rcsum(skb, data_size))) + return 0; + } + return 1; +} + +/** + * llc_rcv - 802.2 entry point from net lower layers + * @skb: received pdu + * @dev: device that receive pdu + * @pt: packet type + * @orig_dev: the original receive net device + * + * When the system receives a 802.2 frame this function is called. It + * checks SAP and connection of received pdu and passes frame to + * llc_{station,sap,conn}_rcv for sending to proper state machine. If + * the frame is related to a busy connection (a connection is sending + * data now), it queues this frame in the connection's backlog. + */ +int llc_rcv(struct sk_buff *skb, struct net_device *dev, + struct packet_type *pt, struct net_device *orig_dev) +{ + struct llc_sap *sap; + struct llc_pdu_sn *pdu; + int dest; + int (*rcv)(struct sk_buff *, struct net_device *, + struct packet_type *, struct net_device *); + void (*sta_handler)(struct sk_buff *skb); + void (*sap_handler)(struct llc_sap *sap, struct sk_buff *skb); + + /* + * When the interface is in promisc. mode, drop all the crap that it + * receives, do not try to analyse it. + */ + if (unlikely(skb->pkt_type == PACKET_OTHERHOST)) { + dprintk("%s: PACKET_OTHERHOST\n", __func__); + goto drop; + } + skb = skb_share_check(skb, GFP_ATOMIC); + if (unlikely(!skb)) + goto out; + if (unlikely(!llc_fixup_skb(skb))) + goto drop; + pdu = llc_pdu_sn_hdr(skb); + if (unlikely(!pdu->dsap)) /* NULL DSAP, refer to station */ + goto handle_station; + sap = llc_sap_find(pdu->dsap); + if (unlikely(!sap)) {/* unknown SAP */ + dprintk("%s: llc_sap_find(%02X) failed!\n", __func__, + pdu->dsap); + goto drop; + } + /* + * First the upper layer protocols that don't need the full + * LLC functionality + */ + rcv = rcu_dereference(sap->rcv_func); + dest = llc_pdu_type(skb); + sap_handler = dest ? READ_ONCE(llc_type_handlers[dest - 1]) : NULL; + if (unlikely(!sap_handler)) { + if (rcv) + rcv(skb, dev, pt, orig_dev); + else + kfree_skb(skb); + } else { + if (rcv) { + struct sk_buff *cskb = skb_clone(skb, GFP_ATOMIC); + if (cskb) + rcv(cskb, dev, pt, orig_dev); + } + sap_handler(sap, skb); + } + llc_sap_put(sap); +out: + return 0; +drop: + kfree_skb(skb); + goto out; +handle_station: + sta_handler = READ_ONCE(llc_station_handler); + if (!sta_handler) + goto drop; + sta_handler(skb); + goto out; +} + +EXPORT_SYMBOL(llc_add_pack); +EXPORT_SYMBOL(llc_remove_pack); +EXPORT_SYMBOL(llc_set_station_handler); -- cgit v1.3.1