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/802/fc.c | 106 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 106 insertions(+) create mode 100644 net/802/fc.c (limited to 'net/802/fc.c') diff --git a/net/802/fc.c b/net/802/fc.c new file mode 100644 index 000000000..afd3d288a --- /dev/null +++ b/net/802/fc.c @@ -0,0 +1,106 @@ +// SPDX-License-Identifier: GPL-2.0-or-later +/* + * NET3: Fibre Channel device handling subroutines + * + * Vineet Abraham + * v 1.0 03/22/99 + */ + +#include +#include +#include +#include +#include +#include +#include +#include +#include +#include +#include +#include +#include +#include +#include +#include +#include +#include + +/* + * Put the headers on a Fibre Channel packet. + */ + +static int fc_header(struct sk_buff *skb, struct net_device *dev, + unsigned short type, + const void *daddr, const void *saddr, unsigned int len) +{ + struct fch_hdr *fch; + int hdr_len; + + /* + * Add the 802.2 SNAP header if IP as the IPv4 code calls + * dev->hard_header directly. + */ + if (type == ETH_P_IP || type == ETH_P_ARP) + { + struct fcllc *fcllc; + + hdr_len = sizeof(struct fch_hdr) + sizeof(struct fcllc); + fch = skb_push(skb, hdr_len); + fcllc = (struct fcllc *)(fch+1); + fcllc->dsap = fcllc->ssap = EXTENDED_SAP; + fcllc->llc = UI_CMD; + fcllc->protid[0] = fcllc->protid[1] = fcllc->protid[2] = 0x00; + fcllc->ethertype = htons(type); + } + else + { + hdr_len = sizeof(struct fch_hdr); + fch = skb_push(skb, hdr_len); + } + + if(saddr) + memcpy(fch->saddr,saddr,dev->addr_len); + else + memcpy(fch->saddr,dev->dev_addr,dev->addr_len); + + if(daddr) + { + memcpy(fch->daddr,daddr,dev->addr_len); + return hdr_len; + } + return -hdr_len; +} + +static const struct header_ops fc_header_ops = { + .create = fc_header, +}; + +static void fc_setup(struct net_device *dev) +{ + dev->header_ops = &fc_header_ops; + dev->type = ARPHRD_IEEE802; + dev->hard_header_len = FC_HLEN; + dev->mtu = 2024; + dev->addr_len = FC_ALEN; + dev->tx_queue_len = 100; /* Long queues on fc */ + dev->flags = IFF_BROADCAST; + + memset(dev->broadcast, 0xFF, FC_ALEN); +} + +/** + * alloc_fcdev - Register fibre channel device + * @sizeof_priv: Size of additional driver-private structure to be allocated + * for this fibre channel device + * + * Fill in the fields of the device structure with fibre channel-generic values. + * + * Constructs a new net device, complete with a private data area of + * size @sizeof_priv. A 32-byte (not bit) alignment is enforced for + * this private data area. + */ +struct net_device *alloc_fcdev(int sizeof_priv) +{ + return alloc_netdev(sizeof_priv, "fc%d", NET_NAME_UNKNOWN, fc_setup); +} +EXPORT_SYMBOL(alloc_fcdev); -- cgit v1.3.1