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/ipv6/rpl.c | 118 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 118 insertions(+) create mode 100644 net/ipv6/rpl.c (limited to 'net/ipv6/rpl.c') diff --git a/net/ipv6/rpl.c b/net/ipv6/rpl.c new file mode 100644 index 000000000..e186998bf --- /dev/null +++ b/net/ipv6/rpl.c @@ -0,0 +1,118 @@ +// SPDX-License-Identifier: GPL-2.0-only +/* + * Authors: + * (C) 2020 Alexander Aring + */ + +#include +#include + +#define IPV6_PFXTAIL_LEN(x) (sizeof(struct in6_addr) - (x)) +#define IPV6_RPL_BEST_ADDR_COMPRESSION 15 + +static void ipv6_rpl_addr_decompress(struct in6_addr *dst, + const struct in6_addr *daddr, + const void *post, unsigned char pfx) +{ + memcpy(dst, daddr, pfx); + memcpy(&dst->s6_addr[pfx], post, IPV6_PFXTAIL_LEN(pfx)); +} + +static void ipv6_rpl_addr_compress(void *dst, const struct in6_addr *addr, + unsigned char pfx) +{ + memcpy(dst, &addr->s6_addr[pfx], IPV6_PFXTAIL_LEN(pfx)); +} + +static void *ipv6_rpl_segdata_pos(const struct ipv6_rpl_sr_hdr *hdr, int i) +{ + return (void *)&hdr->rpl_segdata[i * IPV6_PFXTAIL_LEN(hdr->cmpri)]; +} + +void ipv6_rpl_srh_decompress(struct ipv6_rpl_sr_hdr *outhdr, + const struct ipv6_rpl_sr_hdr *inhdr, + const struct in6_addr *daddr, unsigned char n) +{ + int i; + + outhdr->nexthdr = inhdr->nexthdr; + outhdr->hdrlen = (((n + 1) * sizeof(struct in6_addr)) >> 3); + outhdr->pad = 0; + outhdr->type = inhdr->type; + outhdr->segments_left = inhdr->segments_left; + outhdr->cmpri = 0; + outhdr->cmpre = 0; + + for (i = 0; i < n; i++) + ipv6_rpl_addr_decompress(&outhdr->rpl_segaddr[i], daddr, + ipv6_rpl_segdata_pos(inhdr, i), + inhdr->cmpri); + + ipv6_rpl_addr_decompress(&outhdr->rpl_segaddr[n], daddr, + ipv6_rpl_segdata_pos(inhdr, n), + inhdr->cmpre); +} + +static unsigned char ipv6_rpl_srh_calc_cmpri(const struct ipv6_rpl_sr_hdr *inhdr, + const struct in6_addr *daddr, + unsigned char n) +{ + unsigned char plen; + int i; + + for (plen = 0; plen < sizeof(*daddr); plen++) { + for (i = 0; i < n; i++) { + if (daddr->s6_addr[plen] != + inhdr->rpl_segaddr[i].s6_addr[plen]) + return plen; + } + } + + return IPV6_RPL_BEST_ADDR_COMPRESSION; +} + +static unsigned char ipv6_rpl_srh_calc_cmpre(const struct in6_addr *daddr, + const struct in6_addr *last_segment) +{ + unsigned int plen; + + for (plen = 0; plen < sizeof(*daddr); plen++) { + if (daddr->s6_addr[plen] != last_segment->s6_addr[plen]) + return plen; + } + + return IPV6_RPL_BEST_ADDR_COMPRESSION; +} + +void ipv6_rpl_srh_compress(struct ipv6_rpl_sr_hdr *outhdr, + const struct ipv6_rpl_sr_hdr *inhdr, + const struct in6_addr *daddr, unsigned char n) +{ + unsigned char cmpri, cmpre; + size_t seglen; + int i; + + cmpri = ipv6_rpl_srh_calc_cmpri(inhdr, daddr, n); + cmpre = ipv6_rpl_srh_calc_cmpre(daddr, &inhdr->rpl_segaddr[n]); + + outhdr->nexthdr = inhdr->nexthdr; + seglen = (n * IPV6_PFXTAIL_LEN(cmpri)) + IPV6_PFXTAIL_LEN(cmpre); + outhdr->hdrlen = seglen >> 3; + if (seglen & 0x7) { + outhdr->hdrlen++; + outhdr->pad = 8 - (seglen & 0x7); + } else { + outhdr->pad = 0; + } + outhdr->type = inhdr->type; + outhdr->segments_left = inhdr->segments_left; + outhdr->cmpri = cmpri; + outhdr->cmpre = cmpre; + + for (i = 0; i < n; i++) + ipv6_rpl_addr_compress(ipv6_rpl_segdata_pos(outhdr, i), + &inhdr->rpl_segaddr[i], cmpri); + + ipv6_rpl_addr_compress(ipv6_rpl_segdata_pos(outhdr, n), + &inhdr->rpl_segaddr[n], cmpre); +} -- cgit v1.3.1