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 --- tools/testing/vsock/control.c | 251 ++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 251 insertions(+) create mode 100644 tools/testing/vsock/control.c (limited to 'tools/testing/vsock/control.c') diff --git a/tools/testing/vsock/control.c b/tools/testing/vsock/control.c new file mode 100644 index 000000000..0066e0324 --- /dev/null +++ b/tools/testing/vsock/control.c @@ -0,0 +1,251 @@ +// SPDX-License-Identifier: GPL-2.0-only +/* Control socket for client/server test execution + * + * Copyright (C) 2017 Red Hat, Inc. + * + * Author: Stefan Hajnoczi + */ + +/* The client and server may need to coordinate to avoid race conditions like + * the client attempting to connect to a socket that the server is not + * listening on yet. The control socket offers a communications channel for + * such coordination tasks. + * + * If the client calls control_expectln("LISTENING"), then it will block until + * the server calls control_writeln("LISTENING"). This provides a simple + * mechanism for coordinating between the client and the server. + */ + +#include +#include +#include +#include +#include +#include +#include +#include + +#include "timeout.h" +#include "control.h" +#include "util.h" + +static int control_fd = -1; + +/* Open the control socket, either in server or client mode */ +void control_init(const char *control_host, + const char *control_port, + bool server) +{ + struct addrinfo hints = { + .ai_socktype = SOCK_STREAM, + }; + struct addrinfo *result = NULL; + struct addrinfo *ai; + int ret; + + ret = getaddrinfo(control_host, control_port, &hints, &result); + if (ret != 0) { + fprintf(stderr, "%s\n", gai_strerror(ret)); + exit(EXIT_FAILURE); + } + + for (ai = result; ai; ai = ai->ai_next) { + int fd; + + fd = socket(ai->ai_family, ai->ai_socktype, ai->ai_protocol); + if (fd < 0) + continue; + + if (!server) { + if (connect(fd, ai->ai_addr, ai->ai_addrlen) < 0) + goto next; + control_fd = fd; + printf("Control socket connected to %s:%s.\n", + control_host, control_port); + break; + } + + setsockopt_int_check(fd, SOL_SOCKET, SO_REUSEADDR, 1, + "setsockopt SO_REUSEADDR"); + + if (bind(fd, ai->ai_addr, ai->ai_addrlen) < 0) + goto next; + if (listen(fd, 1) < 0) + goto next; + + printf("Control socket listening on %s:%s\n", + control_host, control_port); + fflush(stdout); + + control_fd = accept(fd, NULL, 0); + close(fd); + + if (control_fd < 0) { + perror("accept"); + exit(EXIT_FAILURE); + } + printf("Control socket connection accepted...\n"); + break; + +next: + close(fd); + } + + if (control_fd < 0) { + fprintf(stderr, "Control socket initialization failed. Invalid address %s:%s?\n", + control_host, control_port); + exit(EXIT_FAILURE); + } + + freeaddrinfo(result); +} + +/* Free resources */ +void control_cleanup(void) +{ + close(control_fd); + control_fd = -1; +} + +/* Write a line to the control socket */ +void control_writeln(const char *str) +{ + ssize_t len = strlen(str); + ssize_t ret; + + timeout_begin(TIMEOUT); + + do { + ret = send(control_fd, str, len, MSG_MORE); + timeout_check("send"); + } while (ret < 0 && errno == EINTR); + + if (ret != len) { + perror("send"); + exit(EXIT_FAILURE); + } + + do { + ret = send(control_fd, "\n", 1, 0); + timeout_check("send"); + } while (ret < 0 && errno == EINTR); + + if (ret != 1) { + perror("send"); + exit(EXIT_FAILURE); + } + + timeout_end(); +} + +void control_writeulong(unsigned long value) +{ + char str[32]; + + if (snprintf(str, sizeof(str), "%lu", value) >= sizeof(str)) { + perror("snprintf"); + exit(EXIT_FAILURE); + } + + control_writeln(str); +} + +unsigned long control_readulong(void) +{ + unsigned long value; + char *str; + + str = control_readln(); + + if (!str) + exit(EXIT_FAILURE); + + value = strtoul(str, NULL, 10); + free(str); + + return value; +} + +/* Return the next line from the control socket (without the trailing newline). + * + * The program terminates if a timeout occurs. + * + * The caller must free() the returned string. + */ +char *control_readln(void) +{ + char *buf = NULL; + size_t idx = 0; + size_t buflen = 0; + + timeout_begin(TIMEOUT); + + for (;;) { + ssize_t ret; + + if (idx >= buflen) { + char *new_buf; + + new_buf = realloc(buf, buflen + 80); + if (!new_buf) { + perror("realloc"); + exit(EXIT_FAILURE); + } + + buf = new_buf; + buflen += 80; + } + + do { + ret = recv(control_fd, &buf[idx], 1, 0); + timeout_check("recv"); + } while (ret < 0 && errno == EINTR); + + if (ret == 0) { + fprintf(stderr, "unexpected EOF on control socket\n"); + exit(EXIT_FAILURE); + } + + if (ret != 1) { + perror("recv"); + exit(EXIT_FAILURE); + } + + if (buf[idx] == '\n') { + buf[idx] = '\0'; + break; + } + + idx++; + } + + timeout_end(); + + return buf; +} + +/* Wait until a given line is received or a timeout occurs */ +void control_expectln(const char *str) +{ + char *line; + + line = control_readln(); + + control_cmpln(line, str, true); + + free(line); +} + +bool control_cmpln(char *line, const char *str, bool fail) +{ + if (strcmp(str, line) == 0) + return true; + + if (fail) { + fprintf(stderr, "expected \"%s\" on control socket, got \"%s\"\n", + str, line); + exit(EXIT_FAILURE); + } + + return false; +} -- cgit v1.3.1