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/ceph/armor.c | 106 +++++++++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 106 insertions(+) create mode 100644 net/ceph/armor.c (limited to 'net/ceph/armor.c') diff --git a/net/ceph/armor.c b/net/ceph/armor.c new file mode 100644 index 000000000..0db806592 --- /dev/null +++ b/net/ceph/armor.c @@ -0,0 +1,106 @@ +// SPDX-License-Identifier: GPL-2.0 + +#include + +int ceph_armor(char *dst, const char *src, const char *end); +int ceph_unarmor(char *dst, const char *src, const char *end); + +/* + * base64 encode/decode. + */ + +static const char *pem_key = + "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/"; + +static int encode_bits(int c) +{ + return pem_key[c]; +} + +static int decode_bits(char c) +{ + if (c >= 'A' && c <= 'Z') + return c - 'A'; + if (c >= 'a' && c <= 'z') + return c - 'a' + 26; + if (c >= '0' && c <= '9') + return c - '0' + 52; + if (c == '+') + return 62; + if (c == '/') + return 63; + if (c == '=') + return 0; /* just non-negative, please */ + return -EINVAL; +} + +int ceph_armor(char *dst, const char *src, const char *end) +{ + int olen = 0; + int line = 0; + + while (src < end) { + unsigned char a, b, c; + + a = *src++; + *dst++ = encode_bits(a >> 2); + if (src < end) { + b = *src++; + *dst++ = encode_bits(((a & 3) << 4) | (b >> 4)); + if (src < end) { + c = *src++; + *dst++ = encode_bits(((b & 15) << 2) | + (c >> 6)); + *dst++ = encode_bits(c & 63); + } else { + *dst++ = encode_bits((b & 15) << 2); + *dst++ = '='; + } + } else { + *dst++ = encode_bits(((a & 3) << 4)); + *dst++ = '='; + *dst++ = '='; + } + olen += 4; + line += 4; + if (line == 64) { + line = 0; + *(dst++) = '\n'; + olen++; + } + } + return olen; +} + +int ceph_unarmor(char *dst, const char *src, const char *end) +{ + int olen = 0; + + while (src < end) { + int a, b, c, d; + + if (src[0] == '\n') { + src++; + continue; + } + if (src + 4 > end) + return -EINVAL; + a = decode_bits(src[0]); + b = decode_bits(src[1]); + c = decode_bits(src[2]); + d = decode_bits(src[3]); + if (a < 0 || b < 0 || c < 0 || d < 0) + return -EINVAL; + + *dst++ = (a << 2) | (b >> 4); + if (src[2] == '=') + return olen + 1; + *dst++ = ((b & 15) << 4) | (c >> 2); + if (src[3] == '=') + return olen + 2; + *dst++ = ((c & 3) << 6) | d; + olen += 3; + src += 4; + } + return olen; +} -- cgit v1.3.1