runc exec: fix setting process.Scheduler

Commit 770728e1 added Scheduler field into both Config and Process,
but forgot to add a mechanism to actually use Process.Scheduler.
As a result, runc exec does not set Process.Scheduler ever.

Fix it, and a test case (which fails before the fix).

Signed-off-by: Kir Kolyshkin <kolyshkin@gmail.com>

CHANGELOG.md

@@ -18,9 +18,10 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
    github.com/moby/sys/user for that. (#3999)
 
 ### Fixed
- * `runc exec -p` no longer ignores specified `ioPriority` setting.
+ * `runc exec -p` no longer ignores specified `ioPriority` and `scheduler`
-   Similarly, libcontainer's `Container.Start` and `Container.Run`
+   settings. Similarly, libcontainer's `Container.Start` and `Container.Run`
-   methods no longer ignore `Process.IOPriority` setting. (#4585)
+   methods no longer ignore `Process.IOPriority` and `Process.Scheduler`
+   settings. (#4585)
 
 ## [1.2.0] - 2024-10-22
 

libcontainer/container_linux.go

@@ -708,6 +708,7 @@ func (c *Container) newInitConfig(process *Process) *initConfig {
 		ProcessLabel:     c.config.ProcessLabel,
 		Rlimits:          c.config.Rlimits,
 		IOPriority:       c.config.IOPriority,
+		Scheduler:        c.config.Scheduler,
 		CreateConsole:    process.ConsoleSocket != nil,
 		ConsoleWidth:     process.ConsoleWidth,
 		ConsoleHeight:    process.ConsoleHeight,
@@ -733,6 +734,9 @@ func (c *Container) newInitConfig(process *Process) *initConfig {
 	if process.IOPriority != nil {
 		cfg.IOPriority = process.IOPriority
 	}
+	if process.Scheduler != nil {
+		cfg.Scheduler = process.Scheduler
+	}
 
 	// Set misc properties.
 

libcontainer/init_linux.go

@@ -82,6 +82,7 @@ type initConfig struct {
 	ProcessLabel    string                `json:"process_label"`
 	Rlimits         []configs.Rlimit      `json:"rlimits"`
 	IOPriority      *configs.IOPriority   `json:"io_priority,omitempty"`
+	Scheduler       *configs.Scheduler    `json:"scheduler,omitempty"`
 
 	// Miscellaneous properties, filled in by [Container.newInitConfig]
 	// unless documented otherwise.
@@ -607,7 +608,7 @@ func setupRlimits(limits []configs.Rlimit, pid int) error {
 	return nil
 }
 
-func setupScheduler(config *configs.Config) error {
+func setupScheduler(config *initConfig) error {
 	if config.Scheduler == nil {
 		return nil
 	}
@@ -616,7 +617,7 @@ func setupScheduler(config *configs.Config) error {
 		return err
 	}
 	if err := unix.SchedSetAttr(0, attr, 0); err != nil {
-		if errors.Is(err, unix.EPERM) && config.Cgroups.CpusetCpus != "" {
+		if errors.Is(err, unix.EPERM) && config.Config.Cgroups.CpusetCpus != "" {
 			return errors.New("process scheduler can't be used together with AllowedCPUs")
 		}
 		return fmt.Errorf("error setting scheduler: %w", err)

libcontainer/process.go

@@ -112,6 +112,9 @@ type Process struct {
 	// For cgroup v2, the only key allowed is "".
 	SubCgroupPaths map[string]string
 
+	// Scheduler represents the scheduling attributes for a process.
+	//
+	// If not empty, takes precedence over container's [configs.Config.Scheduler].
 	Scheduler *configs.Scheduler
 
 	// IOPriority is a process I/O priority.

libcontainer/setns_init_linux.go

@@ -71,7 +71,7 @@ func (l *linuxSetnsInit) Init() error {
 		unix.Umask(int(*l.config.Config.Umask))
 	}
 
-	if err := setupScheduler(l.config.Config); err != nil {
+	if err := setupScheduler(l.config); err != nil {
 		return err
 	}
 

libcontainer/standard_init_linux.go

@@ -155,7 +155,7 @@ func (l *linuxStandardInit) Init() error {
 		}
 	}
 
-	if err := setupScheduler(l.config.Config); err != nil {
+	if err := setupScheduler(l.config); err != nil {
 		return err
 	}
 

tests/integration/scheduler.bats

@@ -12,17 +12,49 @@ function teardown() {
 }
 
 @test "scheduler is applied" {
-	update_config ' .process.scheduler = {"policy": "SCHED_DEADLINE", "nice": 19, "priority": 0, "runtime": 42000, "deadline": 1000000, "period": 1000000, }'
+	update_config ' .process.scheduler = {
+		"policy": "SCHED_BATCH",
+		"priority": 0,
+		"nice": 19
+	}'
 
 	runc run -d --console-socket "$CONSOLE_SOCKET" test_scheduler
 	[ "$status" -eq 0 ]
 
+	# Check init settings.
 	runc exec test_scheduler chrt -p 1
 	[ "$status" -eq 0 ]
-
+	[[ "${lines[0]}" == *"scheduling policy: SCHED_BATCH" ]]
-	[[ "${lines[0]}" == *"scheduling policy: SCHED_DEADLINE" ]]
 	[[ "${lines[1]}" == *"priority: 0" ]]
-	[[ "${lines[2]}" == *"runtime/deadline/period parameters: 42000/1000000/1000000" ]]
+
+	# Check exec settings derived from config.json.
+	runc exec test_scheduler sh -c 'chrt -p $$'
+	[ "$status" -eq 0 ]
+	[[ "${lines[0]}" == *"scheduling policy: SCHED_BATCH" ]]
+	[[ "${lines[1]}" == *"priority: 0" ]]
+
+	# Another exec, with different scheduler settings.
+	proc='
+{
+	"terminal": false,
+	"args": [ "/bin/sleep", "600" ],
+	"cwd": "/",
+	"scheduler": {
+		"policy": "SCHED_DEADLINE",
+		"flags": [ "SCHED_FLAG_RESET_ON_FORK" ],
+		"nice": 19,
+		"priority": 0,
+		"runtime": 42000,
+		"deadline": 100000,
+		"period": 1000000
+	}
+}'
+	__runc exec -d --pid-file pid.txt --process <(echo "$proc") test_scheduler
+
+	run chrt -p "$(cat pid.txt)"
+	[[ "${lines[0]}" == *"scheduling policy: SCHED_DEADLINE|SCHED_RESET_ON_FORK" ]]
+	[[ "${lines[1]}" == *"priority: 0" ]]
+	[[ "${lines[2]}" == *"runtime/deadline/period parameters: 42000/100000/1000000" ]]
 }
 
 # Checks that runc emits a specific error when scheduling policy is used