tracing: selftests: Extend hotplug testing for trace remotes

The hotplug testing only tries reading a trace remote buffer, loaded
before a CPU is offline. Extend this testing to cover:

  * A trace remote buffer loaded after a CPU is offline.
  * A trace remote buffer loaded before a CPU is online.

Because of these added test cases, move the hotplug testing into a
separate hotplug.tc file.

Acked-by: Steven Rostedt (Google) <rostedt@goodmis.org>
Signed-off-by: Vincent Donnefort <vdonnefort@google.com>
Link: https://patch.msgid.link/20260401045100.3394299-3-vdonnefort@google.com
Signed-off-by: Marc Zyngier <maz@kernel.org>

tools/testing/selftests/ftrace/test.d/remotes/functions

@@ -24,12 +24,21 @@ setup_remote_test()
 
 assert_loaded()
 {
-	grep -q "(loaded)" buffer_size_kb
+	grep -q "(loaded)" buffer_size_kb || return 1
 }
 
 assert_unloaded()
 {
-	grep -q "(unloaded)" buffer_size_kb
+	grep -q "(unloaded)" buffer_size_kb || return 1
+}
+
+reload_remote()
+{
+	echo 0 > tracing_on
+	clear_trace
+	assert_unloaded
+	echo 1 > tracing_on
+	assert_loaded
 }
 
 dump_trace_pipe()
@@ -79,10 +88,12 @@ get_cpu_ids()
     sed -n 's/^processor\s*:\s*\([0-9]\+\).*/\1/p' /proc/cpuinfo
 }
 
-get_page_size() {
+get_page_size()
+{
     sed -ne 's/^.*data.*size:\([0-9][0-9]*\).*/\1/p' events/header_page
 }
 
-get_selftest_event_size() {
+get_selftest_event_size()
+{
     sed -ne 's/^.*field:.*;.*size:\([0-9][0-9]*\);.*/\1/p' events/*/selftest/format | awk '{s+=$1} END {print s}'
 }

tools/testing/selftests/ftrace/test.d/remotes/hotplug.tc

@@ -0,0 +1,88 @@
+#!/bin/sh
+# SPDX-License-Identifier: GPL-2.0
+# description: Test trace remote read with an offline CPU
+# requires: remotes/test
+
+. $TEST_DIR/remotes/functions
+
+hotunplug_one_cpu()
+{
+	[ "$(get_cpu_ids | wc -l)" -ge 2 ] || return 1
+
+	for cpu in $(get_cpu_ids); do
+		echo 0 > /sys/devices/system/cpu/cpu$cpu/online || return 1
+		break
+	done
+
+	echo $cpu
+}
+
+# Check non-consuming and consuming read
+check_read()
+{
+    for i in $(seq 1 8); do
+        echo $i > write_event
+    done
+
+    check_trace 1 8 trace
+
+    output=$(dump_trace_pipe)
+    check_trace 1 8 $output
+    rm $output
+}
+
+test_hotplug()
+{
+    echo 0 > trace
+    assert_loaded
+
+    #
+    # Test a trace buffer containing an offline CPU
+    #
+
+    cpu=$(hotunplug_one_cpu) || exit_unsupported
+    trap "echo 1 > /sys/devices/system/cpu/cpu$cpu/online" EXIT
+
+    check_read
+
+    #
+    # Test a trace buffer with a missing CPU
+    #
+
+    reload_remote
+
+    check_read
+
+    #
+    # Test a trace buffer with a CPU added later
+    #
+
+    echo 1 > /sys/devices/system/cpu/cpu$cpu/online
+    trap "" EXIT
+    assert_loaded
+
+    check_read
+
+    # Test if the ring-buffer for the newly added CPU is both writable and
+    # readable
+    for i in $(seq 1 8); do
+        taskset -c $cpu echo $i > write_event
+    done
+
+    cd per_cpu/cpu$cpu/
+
+    check_trace 1 8 trace
+
+    output=$(dump_trace_pipe)
+    check_trace 1 8 $output
+    rm $output
+
+    cd -
+}
+
+if [ -z "$SOURCE_REMOTE_TEST" ]; then
+    set -e
+
+    setup_remote_test
+    test_hotplug
+fi

tools/testing/selftests/ftrace/test.d/remotes/hypervisor/hotplug.tc

@@ -0,0 +1,11 @@
+#!/bin/sh
+# SPDX-License-Identifier: GPL-2.0
+# description: Test hypervisor trace read with an offline CPU
+# requires: remotes/hypervisor/write_event
+
+SOURCE_REMOTE_TEST=1
+. $TEST_DIR/remotes/hotplug.tc
+
+set -e
+setup_remote "hypervisor"
+test_hotplug

tools/testing/selftests/ftrace/test.d/remotes/trace.tc

@@ -58,11 +58,7 @@ test_trace()
     #
 
     # Ensure the writer is not on the reader page by reloading the buffer
-    echo 0 > tracing_on
-    echo 0 > trace
-    assert_unloaded
-    echo 1 > tracing_on
-    assert_loaded
+    reload_remote
 
     # Ensure ring-buffer overflow by emitting events from the same CPU
     for cpu in $(get_cpu_ids); do
@@ -96,27 +92,6 @@ test_trace()
 
         cd - > /dev/null
     done
-
-    #
-    # Test with hotplug
-    #
-
-    [ "$(get_cpu_ids | wc -l)" -ge 2 ] || return 0
-
-    echo 0 > trace
-
-    for cpu in $(get_cpu_ids); do
-        echo 0 > /sys/devices/system/cpu/cpu$cpu/online || return 0
-        break
-    done
-
-    for i in $(seq 1 8); do
-        echo $i > write_event
-    done
-
-    check_trace 1 8 trace
-
-    echo 1 > /sys/devices/system/cpu/cpu$cpu/online
 }
 
 if [ -z "$SOURCE_REMOTE_TEST" ]; then

tools/testing/selftests/ftrace/test.d/remotes/trace_pipe.tc

@@ -92,31 +92,6 @@ test_trace_pipe()
         rm $output
         cd - > /dev/null
     done
-
-    #
-    # Test interaction with hotplug
-    #
-
-    [ "$(get_cpu_ids | wc -l)" -ge 2 ] || return 0
-
-    echo 0 > trace
-
-    for cpu in $(get_cpu_ids); do
-        echo 0 > /sys/devices/system/cpu/cpu$cpu/online || return 0
-        break
-    done
-
-    for i in $(seq 1 8); do
-        echo $i > write_event
-    done
-
-    output=$(dump_trace_pipe)
-
-    check_trace 1 8 $output
-
-    rm $output
-
-    echo 1 > /sys/devices/system/cpu/cpu$cpu/online
 }
 
 if [ -z "$SOURCE_REMOTE_TEST" ]; then