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 --- drivers/net/netdevsim/health.c | 231 +++++++++++++++++++++++++++++++++++++++++ 1 file changed, 231 insertions(+) create mode 100644 drivers/net/netdevsim/health.c (limited to 'drivers/net/netdevsim/health.c') diff --git a/drivers/net/netdevsim/health.c b/drivers/net/netdevsim/health.c new file mode 100644 index 000000000..3bd0e7a48 --- /dev/null +++ b/drivers/net/netdevsim/health.c @@ -0,0 +1,231 @@ +// SPDX-License-Identifier: GPL-2.0 +/* Copyright (c) 2019 Mellanox Technologies. All rights reserved */ + +#include +#include +#include +#include + +#include "netdevsim.h" + +static int +nsim_dev_empty_reporter_dump(struct devlink_health_reporter *reporter, + struct devlink_fmsg *fmsg, void *priv_ctx, + struct netlink_ext_ack *extack) +{ + return 0; +} + +static int +nsim_dev_empty_reporter_diagnose(struct devlink_health_reporter *reporter, + struct devlink_fmsg *fmsg, + struct netlink_ext_ack *extack) +{ + return 0; +} + +static const +struct devlink_health_reporter_ops nsim_dev_empty_reporter_ops = { + .name = "empty", + .dump = nsim_dev_empty_reporter_dump, + .diagnose = nsim_dev_empty_reporter_diagnose, +}; + +struct nsim_dev_dummy_reporter_ctx { + char *break_msg; +}; + +static int +nsim_dev_dummy_reporter_recover(struct devlink_health_reporter *reporter, + void *priv_ctx, + struct netlink_ext_ack *extack) +{ + struct nsim_dev_health *health = devlink_health_reporter_priv(reporter); + struct nsim_dev_dummy_reporter_ctx *ctx = priv_ctx; + + if (health->fail_recover) { + /* For testing purposes, user set debugfs fail_recover + * value to true. Fail right away. + */ + NL_SET_ERR_MSG_MOD(extack, "User setup the recover to fail for testing purposes"); + return -EINVAL; + } + if (ctx) { + kfree(health->recovered_break_msg); + health->recovered_break_msg = kstrdup(ctx->break_msg, + GFP_KERNEL); + if (!health->recovered_break_msg) + return -ENOMEM; + } + return 0; +} + +static int nsim_dev_dummy_fmsg_put(struct devlink_fmsg *fmsg, u32 binary_len) +{ + char *binary; + int i; + + devlink_fmsg_bool_pair_put(fmsg, "test_bool", true); + devlink_fmsg_u8_pair_put(fmsg, "test_u8", 1); + devlink_fmsg_u32_pair_put(fmsg, "test_u32", 3); + devlink_fmsg_u64_pair_put(fmsg, "test_u64", 4); + devlink_fmsg_string_pair_put(fmsg, "test_string", "somestring"); + + binary = kmalloc(binary_len, GFP_KERNEL | __GFP_NOWARN); + if (!binary) + return -ENOMEM; + get_random_bytes(binary, binary_len); + devlink_fmsg_binary_pair_put(fmsg, "test_binary", binary, binary_len); + kfree(binary); + + devlink_fmsg_pair_nest_start(fmsg, "test_nest"); + devlink_fmsg_obj_nest_start(fmsg); + devlink_fmsg_bool_pair_put(fmsg, "nested_test_bool", false); + devlink_fmsg_u8_pair_put(fmsg, "nested_test_u8", false); + devlink_fmsg_obj_nest_end(fmsg); + devlink_fmsg_pair_nest_end(fmsg); + devlink_fmsg_arr_pair_nest_end(fmsg); + devlink_fmsg_arr_pair_nest_start(fmsg, "test_u32_array"); + + for (i = 0; i < 10; i++) + devlink_fmsg_u32_put(fmsg, i); + devlink_fmsg_arr_pair_nest_end(fmsg); + devlink_fmsg_arr_pair_nest_start(fmsg, "test_array_of_objects"); + + for (i = 0; i < 10; i++) { + devlink_fmsg_obj_nest_start(fmsg); + devlink_fmsg_bool_pair_put(fmsg, "in_array_nested_test_bool", + false); + devlink_fmsg_u8_pair_put(fmsg, "in_array_nested_test_u8", i); + devlink_fmsg_obj_nest_end(fmsg); + } + devlink_fmsg_arr_pair_nest_end(fmsg); + + return 0; +} + +static int +nsim_dev_dummy_reporter_dump(struct devlink_health_reporter *reporter, + struct devlink_fmsg *fmsg, void *priv_ctx, + struct netlink_ext_ack *extack) +{ + struct nsim_dev_health *health = devlink_health_reporter_priv(reporter); + struct nsim_dev_dummy_reporter_ctx *ctx = priv_ctx; + + if (ctx) + devlink_fmsg_string_pair_put(fmsg, "break_message", ctx->break_msg); + + return nsim_dev_dummy_fmsg_put(fmsg, health->binary_len); +} + +static int +nsim_dev_dummy_reporter_diagnose(struct devlink_health_reporter *reporter, + struct devlink_fmsg *fmsg, + struct netlink_ext_ack *extack) +{ + struct nsim_dev_health *health = devlink_health_reporter_priv(reporter); + + if (health->recovered_break_msg) + devlink_fmsg_string_pair_put(fmsg, "recovered_break_message", + health->recovered_break_msg); + + return nsim_dev_dummy_fmsg_put(fmsg, health->binary_len); +} + +static const +struct devlink_health_reporter_ops nsim_dev_dummy_reporter_ops = { + .name = "dummy", + .recover = nsim_dev_dummy_reporter_recover, + .dump = nsim_dev_dummy_reporter_dump, + .diagnose = nsim_dev_dummy_reporter_diagnose, +}; + +static ssize_t nsim_dev_health_break_write(struct file *file, + const char __user *data, + size_t count, loff_t *ppos) +{ + struct nsim_dev_health *health = file->private_data; + struct nsim_dev_dummy_reporter_ctx ctx; + char *break_msg; + int err; + + if (count == 0 || count > PAGE_SIZE) + return -EINVAL; + break_msg = memdup_user_nul(data, count); + if (IS_ERR(break_msg)) + return PTR_ERR(break_msg); + + if (break_msg[count - 1] == '\n') + break_msg[count - 1] = '\0'; + + ctx.break_msg = break_msg; + err = devlink_health_report(health->dummy_reporter, break_msg, &ctx); + if (err) + goto out; + +out: + kfree(break_msg); + return err ?: count; +} + +static const struct file_operations nsim_dev_health_break_fops = { + .open = simple_open, + .write = nsim_dev_health_break_write, + .llseek = generic_file_llseek, + .owner = THIS_MODULE, +}; + +int nsim_dev_health_init(struct nsim_dev *nsim_dev, struct devlink *devlink) +{ + struct nsim_dev_health *health = &nsim_dev->health; + int err; + + health->empty_reporter = + devl_health_reporter_create(devlink, + &nsim_dev_empty_reporter_ops, + health); + if (IS_ERR(health->empty_reporter)) + return PTR_ERR(health->empty_reporter); + + health->dummy_reporter = + devl_health_reporter_create(devlink, + &nsim_dev_dummy_reporter_ops, + health); + if (IS_ERR(health->dummy_reporter)) { + err = PTR_ERR(health->dummy_reporter); + goto err_empty_reporter_destroy; + } + + health->ddir = debugfs_create_dir("health", nsim_dev->ddir); + if (IS_ERR(health->ddir)) { + err = PTR_ERR(health->ddir); + goto err_dummy_reporter_destroy; + } + + health->recovered_break_msg = NULL; + debugfs_create_file("break_health", 0200, health->ddir, health, + &nsim_dev_health_break_fops); + health->binary_len = 16; + debugfs_create_u32("binary_len", 0600, health->ddir, + &health->binary_len); + health->fail_recover = false; + debugfs_create_bool("fail_recover", 0600, health->ddir, + &health->fail_recover); + return 0; + +err_dummy_reporter_destroy: + devl_health_reporter_destroy(health->dummy_reporter); +err_empty_reporter_destroy: + devl_health_reporter_destroy(health->empty_reporter); + return err; +} + +void nsim_dev_health_exit(struct nsim_dev *nsim_dev) +{ + struct nsim_dev_health *health = &nsim_dev->health; + + debugfs_remove_recursive(health->ddir); + kfree(health->recovered_break_msg); + devl_health_reporter_destroy(health->dummy_reporter); + devl_health_reporter_destroy(health->empty_reporter); +} -- cgit v1.3.1