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/char/tpm/tpm-dev.c | 67 ++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 67 insertions(+) create mode 100644 drivers/char/tpm/tpm-dev.c (limited to 'drivers/char/tpm/tpm-dev.c') diff --git a/drivers/char/tpm/tpm-dev.c b/drivers/char/tpm/tpm-dev.c new file mode 100644 index 000000000..74488f0a7 --- /dev/null +++ b/drivers/char/tpm/tpm-dev.c @@ -0,0 +1,67 @@ +// SPDX-License-Identifier: GPL-2.0-only +/* + * Copyright (C) 2004 IBM Corporation + * Authors: + * Leendert van Doorn + * Dave Safford + * Reiner Sailer + * Kylene Hall + * + * Copyright (C) 2013 Obsidian Research Corp + * Jason Gunthorpe + * + * Device file system interface to the TPM + */ +#include +#include "tpm-dev.h" + +static int tpm_open(struct inode *inode, struct file *file) +{ + struct tpm_chip *chip; + struct file_priv *priv; + + chip = container_of(inode->i_cdev, struct tpm_chip, cdev); + + /* It's assured that the chip will be opened just once, + * by the check of is_open variable, which is protected + * by driver_lock. */ + if (test_and_set_bit(0, &chip->is_open)) { + dev_dbg(&chip->dev, "Another process owns this TPM\n"); + return -EBUSY; + } + + priv = kzalloc_obj(*priv); + if (priv == NULL) + goto out; + + tpm_common_open(file, chip, priv, NULL); + + return nonseekable_open(inode, file); + + out: + clear_bit(0, &chip->is_open); + return -ENOMEM; +} + +/* + * Called on file close + */ +static int tpm_release(struct inode *inode, struct file *file) +{ + struct file_priv *priv = file->private_data; + + tpm_common_release(file, priv); + clear_bit(0, &priv->chip->is_open); + kfree(priv); + + return 0; +} + +const struct file_operations tpm_fops = { + .owner = THIS_MODULE, + .open = tpm_open, + .read = tpm_common_read, + .write = tpm_common_write, + .poll = tpm_common_poll, + .release = tpm_release, +}; -- cgit v1.3.1