libct/cg/v1: solution to the failure of setting rt_period_us and rt_r…

…untime_us

As reported in issue opencontainers#4094, sometimes setting rt_period_us and rt_runtime_us
at the same time will fail. The reason is that in cgroupv1, these two values
cannot be set atomically.

Sometimes setting rt_period_us and rt_runtime_us at the same time will fail.
The reason is that in cgroupv1, these two values cannot be set atomically.

When we set a new rt_period_us (called period_new), the kernel will determine
whether the current configuration of new_limit1 = old_quota/new_period exceeds
the limit. If it exceeds the limit, an error will be reported. Maybe it is reasonable
to set rt_runtime_us first, new_limit2 = new_quota/old_period.
for example:
The original state of cgv1 is rt_period_us: 10000 rt_runtime_us: 5000
The user wants to change it to rt_period_us: 1000 rt_runtime_us:300.
The new rt_runtime_us should be set first.

In the opposite case, if rt_runtime_us is set first, new_limit2 may still exceed the
limit, but new_limit1 will be valid.
for example:
The original state of cgv1 is rt_period_us: 1000 rt_runtime_us: 500
The user wants to change it to rt_period_us: 10000 rt_runtime_us:3000.
The new rt_period_us should be set first.

Therefore, new_limit1 and new_limit2 should be calculated in advance, and the smaller
corresponding setting order should be selected to set rt_period_us and rt_runtime_us.

Signed-off-by: ls-ggg <335814617@qq.com>

libcontainer/cgroups/fs/cpu.go

@@ -6,6 +6,7 @@ import (
 	"fmt"
 	"os"
 	"strconv"
+	"strings"
 
 	"github.com/opencontainers/runc/libcontainer/cgroups"
 	"github.com/opencontainers/runc/libcontainer/cgroups/fscommon"
@@ -35,17 +36,60 @@ func (s *CpuGroup) Apply(path string, r *configs.Resources, pid int) error {
 }
 
 func (s *CpuGroup) SetRtSched(path string, r *configs.Resources) error {
-	if r.CpuRtPeriod != 0 {
-		if err := cgroups.WriteFile(path, "cpu.rt_period_us", strconv.FormatUint(r.CpuRtPeriod, 10)); err != nil {
+	const (
+		filePeriod  = "cpu.rt_period_us"
+		fileRuntime = "cpu.rt_runtime_us"
+	)
+
+	if r.CpuRtPeriod == 0 && r.CpuRtRuntime == 0 {
+		return nil
+	}
+
+	if r.CpuRtPeriod != 0 && r.CpuRtRuntime == 0 {
+		return cgroups.WriteFile(path, filePeriod, strconv.FormatUint(r.CpuRtPeriod, 10))
+	} else if r.CpuRtRuntime != 0 && r.CpuRtPeriod == 0 {
+		return cgroups.WriteFile(path, fileRuntime, strconv.FormatInt(r.CpuRtRuntime, 10))
+	}
+
+	// When neither CpuRtPeriod nor CpuRtRuntime is equal to 0, let's set them in the correct order
+
+	sOldPeriod, err := cgroups.ReadFile(path, filePeriod)
+	if err != nil {
+		return err
+	}
+	oldPeriod, err := strconv.ParseInt(strings.TrimSpace(sOldPeriod), 10, 64)
+	if err != nil {
+		return err
+	}
+
+	sOldRuntime, err := cgroups.ReadFile(path, fileRuntime)
+	if err != nil {
+		return err
+	}
+	oldRuntime, err := strconv.ParseInt(strings.TrimSpace(sOldRuntime), 10, 64)
+	if err != nil {
+		return err
+	}
+
+	/*
+		set the cpu.rt_period_us and cpu.rt_runtime_us in the optimal order and
+		try to keep the ratio of the intermediate state within the limit.
+	*/
+
+	// First set cpu.rt_period_us because of (oldRuntime / r.CpuRtPeriod) < (r.CpuRtRuntime / oldPeriod)
+	if uint64(oldRuntime*oldPeriod) < (uint64(r.CpuRtRuntime) * r.CpuRtPeriod) {
+		if err := cgroups.WriteFile(path, filePeriod, strconv.FormatUint(r.CpuRtPeriod, 10)); err != nil {
 			return err
 		}
-	}
-	if r.CpuRtRuntime != 0 {
-		if err := cgroups.WriteFile(path, "cpu.rt_runtime_us", strconv.FormatInt(r.CpuRtRuntime, 10)); err != nil {
+		if err := cgroups.WriteFile(path, fileRuntime, strconv.FormatInt(r.CpuRtRuntime, 10)); err != nil {
 			return err
 		}
 	}
-	return nil
+	// First set cpu.rt_runtime_us because of (r.CpuRtRuntime / oldPeriod) < (oldRuntime / r.CpuRtPeriod)
+	if err := cgroups.WriteFile(path, fileRuntime, strconv.FormatInt(r.CpuRtRuntime, 10)); err != nil {
+		return err
+	}
+	return cgroups.WriteFile(path, filePeriod, strconv.FormatUint(r.CpuRtPeriod, 10))
 }
 
 func (s *CpuGroup) Set(path string, r *configs.Resources) error {

tests/integration/update.bats

@@ -758,6 +758,16 @@ EOF
 
 	check_cgroup_value "cpu.rt_period_us" 900001
 	check_cgroup_value "cpu.rt_runtime_us" 600001
+
+	runc update test_update_rt --cpu-rt-period 10000 --cpu-rt-runtime 3000
+    	[ "$status" -eq 0 ]
+	check_cgroup_value "cpu.rt_period_us" 10000
+	check_cgroup_value "cpu.rt_runtime_us" 3000
+
+    	runc update test_update_rt --cpu-rt-period 100000 --cpu-rt-runtime 20000
+    	[ "$status" -eq 0 ]
+    	check_cgroup_value "cpu.rt_period_us" 100000
+    	check_cgroup_value "cpu.rt_runtime_us" 20000
 }
 
 @test "update devices [minimal transition rules]" {