sched/cache: Keep nr_pref_llc_running in the runnable domain, to fix LLC mis-scheduling buggrafted

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 <zhanxusheng@xiaomi.com>
Suggested-by: Chen Yu <yu.c.chen@intel.com>
Signed-off-by: Tim Chen <tim.c.chen@linux.intel.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Reviewed-by: Kayra Cizmeci <kayracizmeci@gmail.com>
Cc: <stable@kernel.org> # v7.2.x
Link: https://patch.msgid.link/06af61afedac32e6477f57feb4d658f6c411c3af.1790035273.git.tim.c.chen@linux.intel.com

1 files changed, 380 insertions, 0 deletions

diff --git a/tools/perf/util/namespaces.c b/tools/perf/util/namespaces.c
new file mode 100644
index 000000000..01502570b
--- /dev/null
+++ b/tools/perf/util/namespaces.c
@@ -0,0 +1,380 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ *
+ * Copyright (C) 2017 Hari Bathini, IBM Corporation
+ */
+
+#include "namespaces.h"
+#include "event.h"
+#include <sys/types.h>
+#include <sys/stat.h>
+#include <fcntl.h>
+#include <limits.h>
+#include <sched.h>
+#include <stdlib.h>
+#include <stdio.h>
+#include <string.h>
+#include <unistd.h>
+#include <asm/bug.h>
+#include <linux/kernel.h>
+#include <linux/zalloc.h>
+
+static const char *perf_ns__names[] = {
+	[NET_NS_INDEX]		= "net",
+	[UTS_NS_INDEX]		= "uts",
+	[IPC_NS_INDEX]		= "ipc",
+	[PID_NS_INDEX]		= "pid",
+	[USER_NS_INDEX]		= "user",
+	[MNT_NS_INDEX]		= "mnt",
+	[CGROUP_NS_INDEX]	= "cgroup",
+};
+
+const char *perf_ns__name(unsigned int id)
+{
+	if (id >= ARRAY_SIZE(perf_ns__names))
+		return "UNKNOWN";
+	return perf_ns__names[id];
+}
+
+struct namespaces *namespaces__new(struct perf_record_namespaces *event)
+{
+	struct namespaces *namespaces;
+	u64 link_info_size = ((event ? event->nr_namespaces : NR_NAMESPACES) *
+			      sizeof(struct perf_ns_link_info));
+
+	namespaces = zalloc(sizeof(struct namespaces) + link_info_size);
+	if (!namespaces)
+		return NULL;
+
+	namespaces->end_time = -1;
+
+	if (event)
+		memcpy(namespaces->link_info, event->link_info, link_info_size);
+
+	return namespaces;
+}
+
+void namespaces__free(struct namespaces *namespaces)
+{
+	free(namespaces);
+}
+
+static int nsinfo__get_nspid(pid_t *tgid, pid_t *nstgid, bool *in_pidns, const char *path)
+{
+	FILE *f = NULL;
+	char *statln = NULL;
+	size_t linesz = 0;
+	char *nspid;
+
+	f = fopen(path, "r");
+	if (f == NULL)
+		return -1;
+
+	while (getline(&statln, &linesz, f) != -1) {
+		/* Use tgid if CONFIG_PID_NS is not defined. */
+		if (strstr(statln, "Tgid:") != NULL) {
+			*tgid = (pid_t)strtol(strrchr(statln, '\t'), NULL, 10);
+			*nstgid = *tgid;
+		}
+
+		if (strstr(statln, "NStgid:") != NULL) {
+			nspid = strrchr(statln, '\t');
+			*nstgid = (pid_t)strtol(nspid, NULL, 10);
+			/*
+			 * If innermost tgid is not the first, process is in a different
+			 * PID namespace.
+			 */
+			*in_pidns = (statln + sizeof("NStgid:") - 1) != nspid;
+			break;
+		}
+	}
+
+	fclose(f);
+	free(statln);
+	return 0;
+}
+
+int nsinfo__init(struct nsinfo *nsi)
+{
+	char oldns[PATH_MAX];
+	char spath[PATH_MAX];
+	char *newns = NULL;
+	struct stat old_stat;
+	struct stat new_stat;
+	int rv = -1;
+
+	if (snprintf(oldns, PATH_MAX, "/proc/self/ns/mnt") >= PATH_MAX)
+		return rv;
+
+	if (asprintf(&newns, "/proc/%d/ns/mnt", nsinfo__pid(nsi)) == -1)
+		return rv;
+
+	if (stat(oldns, &old_stat) < 0)
+		goto out;
+
+	if (stat(newns, &new_stat) < 0)
+		goto out;
+
+	/* Check if the mount namespaces differ, if so then indicate that we
+	 * want to switch as part of looking up dso/map data.
+	 */
+	if (old_stat.st_ino != new_stat.st_ino) {
+		RC_CHK_ACCESS(nsi)->need_setns = true;
+		RC_CHK_ACCESS(nsi)->mntns_path = newns;
+		newns = NULL;
+	}
+
+	/* If we're dealing with a process that is in a different PID namespace,
+	 * attempt to work out the innermost tgid for the process.
+	 */
+	if (snprintf(spath, PATH_MAX, "/proc/%d/status", nsinfo__pid(nsi)) >= PATH_MAX)
+		goto out;
+
+	rv = nsinfo__get_nspid(&RC_CHK_ACCESS(nsi)->tgid, &RC_CHK_ACCESS(nsi)->nstgid,
+			       &RC_CHK_ACCESS(nsi)->in_pidns, spath);
+
+out:
+	free(newns);
+	return rv;
+}
+
+static struct nsinfo *nsinfo__alloc(void)
+{
+	struct nsinfo *res;
+	RC_STRUCT(nsinfo) *nsi;
+
+	nsi = calloc(1, sizeof(*nsi));
+	if (ADD_RC_CHK(res, nsi))
+		refcount_set(&nsi->refcnt, 1);
+
+	return res;
+}
+
+struct nsinfo *nsinfo__new(pid_t pid)
+{
+	struct nsinfo *nsi;
+
+	if (pid == 0)
+		return NULL;
+
+	nsi = nsinfo__alloc();
+	if (!nsi)
+		return NULL;
+
+	RC_CHK_ACCESS(nsi)->pid = pid;
+	RC_CHK_ACCESS(nsi)->tgid = pid;
+	RC_CHK_ACCESS(nsi)->nstgid = pid;
+	nsinfo__clear_need_setns(nsi);
+	RC_CHK_ACCESS(nsi)->in_pidns = false;
+	/* Init may fail if the process exits while we're trying to look at its
+	 * proc information. In that case, save the pid but don't try to enter
+	 * the namespace.
+	 */
+	if (nsinfo__init(nsi) == -1)
+		nsinfo__clear_need_setns(nsi);
+
+	return nsi;
+}
+
+static const char *nsinfo__mntns_path(const struct nsinfo *nsi)
+{
+	return RC_CHK_ACCESS(nsi)->mntns_path;
+}
+
+struct nsinfo *nsinfo__copy(const struct nsinfo *nsi)
+{
+	struct nsinfo *nnsi;
+
+	if (nsi == NULL)
+		return NULL;
+
+	nnsi = nsinfo__alloc();
+	if (!nnsi)
+		return NULL;
+
+	RC_CHK_ACCESS(nnsi)->pid = nsinfo__pid(nsi);
+	RC_CHK_ACCESS(nnsi)->tgid = nsinfo__tgid(nsi);
+	RC_CHK_ACCESS(nnsi)->nstgid = nsinfo__nstgid(nsi);
+	RC_CHK_ACCESS(nnsi)->need_setns = nsinfo__need_setns(nsi);
+	RC_CHK_ACCESS(nnsi)->in_pidns = nsinfo__in_pidns(nsi);
+	if (nsinfo__mntns_path(nsi)) {
+		RC_CHK_ACCESS(nnsi)->mntns_path = strdup(nsinfo__mntns_path(nsi));
+		if (!RC_CHK_ACCESS(nnsi)->mntns_path) {
+			nsinfo__put(nnsi);
+			return NULL;
+		}
+	}
+
+	return nnsi;
+}
+
+static refcount_t *nsinfo__refcnt(struct nsinfo *nsi)
+{
+	return &RC_CHK_ACCESS(nsi)->refcnt;
+}
+
+static void nsinfo__delete(struct nsinfo *nsi)
+{
+	if (nsi) {
+		WARN_ONCE(refcount_read(nsinfo__refcnt(nsi)) != 0, "nsinfo refcnt unbalanced\n");
+		zfree(&RC_CHK_ACCESS(nsi)->mntns_path);
+		RC_CHK_FREE(nsi);
+	}
+}
+
+struct nsinfo *nsinfo__get(struct nsinfo *nsi)
+{
+	struct nsinfo *result;
+
+	if (RC_CHK_GET(result, nsi))
+		refcount_inc(nsinfo__refcnt(nsi));
+
+	return result;
+}
+
+void nsinfo__put(struct nsinfo *nsi)
+{
+	if (nsi && refcount_dec_and_test(nsinfo__refcnt(nsi)))
+		nsinfo__delete(nsi);
+	else
+		RC_CHK_PUT(nsi);
+}
+
+bool nsinfo__need_setns(const struct nsinfo *nsi)
+{
+	return RC_CHK_ACCESS(nsi)->need_setns;
+}
+
+void nsinfo__clear_need_setns(struct nsinfo *nsi)
+{
+	RC_CHK_ACCESS(nsi)->need_setns = false;
+}
+
+pid_t nsinfo__tgid(const struct nsinfo  *nsi)
+{
+	return RC_CHK_ACCESS(nsi)->tgid;
+}
+
+pid_t nsinfo__nstgid(const struct nsinfo  *nsi)
+{
+	return RC_CHK_ACCESS(nsi)->nstgid;
+}
+
+pid_t nsinfo__pid(const struct nsinfo  *nsi)
+{
+	return RC_CHK_ACCESS(nsi)->pid;
+}
+
+bool nsinfo__in_pidns(const struct nsinfo *nsi)
+{
+	return RC_CHK_ACCESS(nsi)->in_pidns;
+}
+
+void nsinfo__set_in_pidns(struct nsinfo *nsi)
+{
+	RC_CHK_ACCESS(nsi)->in_pidns = true;
+}
+
+void nsinfo__mountns_enter(struct nsinfo *nsi,
+				  struct nscookie *nc)
+{
+	char curpath[PATH_MAX];
+	int oldns = -1;
+	int newns = -1;
+	char *oldcwd = NULL;
+
+	if (nc == NULL)
+		return;
+
+	nc->oldns = -1;
+	nc->newns = -1;
+
+	if (!nsi || !nsinfo__need_setns(nsi))
+		return;
+
+	if (!getcwd(curpath, sizeof(curpath)))
+		return;
+
+	oldcwd = strdup(curpath);
+	if (!oldcwd)
+		return;
+
+	oldns = open("/proc/self/ns/mnt", O_RDONLY);
+	if (oldns < 0)
+		goto errout;
+
+	newns = open(nsinfo__mntns_path(nsi), O_RDONLY);
+	if (newns < 0)
+		goto errout;
+
+	if (setns(newns, CLONE_NEWNS) < 0)
+		goto errout;
+
+	nc->oldcwd = oldcwd;
+	nc->oldns = oldns;
+	nc->newns = newns;
+	return;
+
+errout:
+	free(oldcwd);
+	if (oldns > -1)
+		close(oldns);
+	if (newns > -1)
+		close(newns);
+}
+
+void nsinfo__mountns_exit(struct nscookie *nc)
+{
+	if (nc == NULL || nc->oldns == -1 || nc->newns == -1 || !nc->oldcwd)
+		return;
+
+	setns(nc->oldns, CLONE_NEWNS);
+
+	if (nc->oldcwd) {
+		WARN_ON_ONCE(chdir(nc->oldcwd));
+		zfree(&nc->oldcwd);
+	}
+
+	if (nc->oldns > -1) {
+		close(nc->oldns);
+		nc->oldns = -1;
+	}
+
+	if (nc->newns > -1) {
+		close(nc->newns);
+		nc->newns = -1;
+	}
+}
+
+char *nsinfo__realpath(const char *path, struct nsinfo *nsi)
+{
+	char *rpath;
+	struct nscookie nsc;
+
+	nsinfo__mountns_enter(nsi, &nsc);
+	rpath = realpath(path, NULL);
+	nsinfo__mountns_exit(&nsc);
+
+	return rpath;
+}
+
+int nsinfo__stat(const char *filename, struct stat *st, struct nsinfo *nsi)
+{
+	int ret;
+	struct nscookie nsc;
+
+	nsinfo__mountns_enter(nsi, &nsc);
+	ret = stat(filename, st);
+	nsinfo__mountns_exit(&nsc);
+
+	return ret;
+}
+
+bool nsinfo__is_in_root_namespace(void)
+{
+	pid_t tgid = 0, nstgid = 0;
+	bool in_pidns = false;
+
+	nsinfo__get_nspid(&tgid, &nstgid, &in_pidns, "/proc/self/status");
+	return !in_pidns;
+}