cgroup/cpuset: Expose cpuset.cpus.isolated

The root-only cpuset.cpus.isolated control file shows the current set
of isolated CPUs in isolated partitions. This control file is currently
exposed only with the cgroup_debug boot command line option which also
adds the ".__DEBUG__." prefix. This is actually a useful control file if
users want to find out which CPUs are currently in an isolated state by
the cpuset controller. Remove CFTYPE_DEBUG flag for this control file and
make it available by default without any prefix.

The test_cpuset_prs.sh test script and the cgroup-v2.rst documentation
file are also updated accordingly. Minor code change is also made in
test_cpuset_prs.sh to avoid false test failure when running on debug
kernel.

Signed-off-by: Waiman Long <[e-mail]>
Signed-off-by: Tejun Heo <[e-mail]>

Documentation/admin-guide/cgroup-v2.rst

···
 	treated to have an implicit value of "cpuset.cpus" in the
 	formation of local partition.
 
+  cpuset.cpus.isolated
+	A read-only and root cgroup only multiple values file.
+
+	This file shows the set of all isolated CPUs used in existing
+	isolated partitions. It will be empty if no isolated partition
+	is created.
+
   cpuset.cpus.partition
 	A read-write single value file which exists on non-root
 	cpuset-enabled cgroups.  This flag is owned by the parent cgroup

kernel/cgroup/cpuset.c

···
 		.name = "cpus.isolated",
 		.seq_show = cpuset_common_seq_show,
 		.private = FILE_ISOLATED_CPULIST,
-		.flags = CFTYPE_ONLY_ON_ROOT | CFTYPE_DEBUG,
+		.flags = CFTYPE_ONLY_ON_ROOT,
 	},
 
 	{ }	/* terminate */

tools/testing/selftests/cgroup/test_cpuset_prs.sh

···
 		XECPUS=$DIR/cpuset.cpus.exclusive.effective
 		PRS=$DIR/cpuset.cpus.partition
 		PCPUS=$DIR/.__DEBUG__.cpuset.cpus.subpartitions
-		ISCPUS=$DIR/.__DEBUG__.cpuset.cpus.isolated
+		ISCPUS=$DIR/cpuset.cpus.isolated
 		[[ -e $CPUS   ]] && echo "$CPUS: $(cat $CPUS)"
 		[[ -e $XCPUS  ]] && echo "$XCPUS: $(cat $XCPUS)"
 		[[ -e $ECPUS  ]] && echo "$ECPUS: $(cat $ECPUS)"
···
 
 #
 # Get isolated (including offline) CPUs by looking at
-# /sys/kernel/debug/sched/domains and *cpuset.cpus.isolated control file,
+# /sys/kernel/debug/sched/domains and cpuset.cpus.isolated control file,
 # if available, and compare that with the expected value.
 #
 # Note that isolated CPUs from the sched/domains context include offline
 # CPUs as well as CPUs in non-isolated 1-CPU partition. Those CPUs may
-# not be included in the *cpuset.cpus.isolated control file which contains
+# not be included in the cpuset.cpus.isolated control file which contains
 # only CPUs in isolated partitions.
 #
 # $1 - expected isolated cpu list(s) <isolcpus1>{,<isolcpus2>}
 # <isolcpus1> - expected sched/domains value
-# <isolcpus2> - *cpuset.cpus.isolated value = <isolcpus1> if not defined
+# <isolcpus2> - cpuset.cpus.isolated value = <isolcpus1> if not defined
 #
 check_isolcpus()
 {
···
 	ISOLCPUS=
 	LASTISOLCPU=
 	SCHED_DOMAINS=/sys/kernel/debug/sched/domains
-	ISCPUS=${CGROUP2}/.__DEBUG__.cpuset.cpus.isolated
+	ISCPUS=${CGROUP2}/cpuset.cpus.isolated
 	if [[ $EXPECT_VAL = . ]]
 	then
 		EXPECT_VAL=
···
 null_isolcpus_check()
 {
 	[[ $VERBOSE -gt 0 ]] || return 0
-	pause 0.02
-	check_isolcpus "."
-	if [[ $? -ne 0 ]]
-	then
-		echo "Unexpected isolated CPUs: $ISOLCPUS"
-		dump_states
-		exit 1
-	fi
+	# Retry a few times before printing error
+	RETRY=0
+	while [[ $RETRY -lt 5 ]]
+	do
+		pause 0.01
+		check_isolcpus "."
+		[[ $? -eq 0 ]] && return 0
+		((RETRY++))
+	done
+	echo "Unexpected isolated CPUs: $ISOLCPUS"
+	dump_states
+	exit 1
 }
 
 #
···
 		#
 		NEWLIST=$(cat cpuset.cpus.effective)
 		RETRY=0
-		while [[ $NEWLIST != $CPULIST && $RETRY -lt 5 ]]
+		while [[ $NEWLIST != $CPULIST && $RETRY -lt 8 ]]
 		do
 			# Wait a bit longer & recheck a few times
 			pause 0.01