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 --- fs/cachefiles/security.c | 112 +++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 112 insertions(+) create mode 100644 fs/cachefiles/security.c (limited to 'fs/cachefiles/security.c') diff --git a/fs/cachefiles/security.c b/fs/cachefiles/security.c new file mode 100644 index 000000000..fc6611886 --- /dev/null +++ b/fs/cachefiles/security.c @@ -0,0 +1,112 @@ +// SPDX-License-Identifier: GPL-2.0-or-later +/* CacheFiles security management + * + * Copyright (C) 2007, 2021 Red Hat, Inc. All Rights Reserved. + * Written by David Howells (dhowells@redhat.com) + */ + +#include +#include +#include "internal.h" + +/* + * determine the security context within which we access the cache from within + * the kernel + */ +int cachefiles_get_security_ID(struct cachefiles_cache *cache) +{ + struct cred *new; + int ret; + + _enter("{%u}", cache->have_secid ? cache->secid : 0); + + new = prepare_kernel_cred(current); + if (!new) { + ret = -ENOMEM; + goto error; + } + + if (cache->have_secid) { + ret = set_security_override(new, cache->secid); + if (ret < 0) { + put_cred(new); + pr_err("Security denies permission to nominate security context: error %d\n", + ret); + goto error; + } + } + + cache->cache_cred = new; + ret = 0; +error: + _leave(" = %d", ret); + return ret; +} + +/* + * see if mkdir and create can be performed in the root directory + */ +static int cachefiles_check_cache_dir(struct cachefiles_cache *cache, + struct dentry *root) +{ + int ret; + + ret = security_inode_mkdir(d_backing_inode(root), root, 0); + if (ret < 0) { + pr_err("Security denies permission to make dirs: error %d", + ret); + return ret; + } + + ret = security_inode_create(d_backing_inode(root), root, 0); + if (ret < 0) + pr_err("Security denies permission to create files: error %d", + ret); + + return ret; +} + +/* + * check the security details of the on-disk cache + * - must be called with security override in force + * - must return with a security override in force - even in the case of an + * error + */ +int cachefiles_determine_cache_security(struct cachefiles_cache *cache, + struct dentry *root, + const struct cred **_saved_cred) +{ + struct cred *new; + int ret; + + _enter(""); + + /* duplicate the cache creds for COW (the override is currently in + * force, so we can use prepare_creds() to do this) */ + new = prepare_creds(); + if (!new) + return -ENOMEM; + + cachefiles_end_secure(cache, *_saved_cred); + + /* use the cache root dir's security context as the basis with + * which create files */ + ret = set_create_files_as(new, d_backing_inode(root)); + if (ret < 0) { + abort_creds(new); + cachefiles_begin_secure(cache, _saved_cred); + _leave(" = %d [cfa]", ret); + return ret; + } + + put_cred(cache->cache_cred); + cache->cache_cred = new; + + cachefiles_begin_secure(cache, _saved_cred); + ret = cachefiles_check_cache_dir(cache, root); + + if (ret == -EOPNOTSUPP) + ret = 0; + _leave(" = %d", ret); + return ret; +} -- cgit v1.3.1