Setup a reasonable default for pids-limit 4096

CRI-O defaults to 1024 for the maximum pids in a container.  Podman
should have a similar limit. Once we have a containers.conf, we can
set the limit in this file, and have it easily customizable.

Currently the documentation says that -1 sets pids-limit=max, but -1 fails.
This patch allows -1, but also indicates that 0 also sets the max pids limit.

Signed-off-by: Daniel J Walsh <dwalsh@redhat.com>

7 files changed, 51 insertions, 12 deletions

diff --git a/cmd/podman/common.go b/cmd/podman/common.go
index 0115e6ef1..2a3f8f3ad 100644
--- a/cmd/podman/common.go
+++ b/cmd/podman/common.go
@@ -11,6 +11,7 @@ import (
 	"github.com/containers/libpod/cmd/podman/shared"
 	"github.com/containers/libpod/libpod/define"
 	"github.com/containers/libpod/pkg/rootless"
+	"github.com/containers/libpod/pkg/sysinfo"
 	"github.com/fatih/camelcase"
 	jsoniter "github.com/json-iterator/go"
 	"github.com/pkg/errors"
@@ -374,8 +375,8 @@ func getCreateFlags(c *cliconfig.PodmanCommand) {
 		"PID namespace to use",
 	)
 	createFlags.Int64(
-		"pids-limit", 0,
-		"Tune container pids limit (set -1 for unlimited)",
+		"pids-limit", sysinfo.GetDefaultPidsLimit(),
+		"Tune container pids limit (set 0 for unlimited)",
 	)
 	createFlags.String(
 		"pod", "",
diff --git a/cmd/podman/shared/create.go b/cmd/podman/shared/create.go
index fc8197721..f36295054 100644
--- a/cmd/podman/shared/create.go
+++ b/cmd/podman/shared/create.go
@@ -686,6 +686,11 @@ func ParseCreateOpts(ctx context.Context, c *GenericCLIResults, runtime *libpod.
 		logDriver = c.String("log-driver")
 	}
 
+	pidsLimit := c.Int64("pids-limit")
+	if c.String("cgroups") == "disabled" && !c.Changed("pids-limit") {
+		pidsLimit = 0
+	}
+
 	config := &cc.CreateConfig{
 		Annotations:       annotations,
 		BuiltinImgVolumes: ImageVolumes,
@@ -764,7 +769,7 @@ func ParseCreateOpts(ctx context.Context, c *GenericCLIResults, runtime *libpod.
 			MemorySwappiness:  int(memorySwappiness),
 			KernelMemory:      memoryKernel,
 			OomScoreAdj:       c.Int("oom-score-adj"),
-			PidsLimit:         c.Int64("pids-limit"),
+			PidsLimit:         pidsLimit,
 			Ulimit:            c.StringSlice("ulimit"),
 		},
 		RestartPolicy: c.String("restart"),
diff --git a/docs/podman-create.1.md b/docs/podman-create.1.md
index c088f3e94..46fa4fcd4 100644
--- a/docs/podman-create.1.md
+++ b/docs/podman-create.1.md
@@ -552,7 +552,7 @@ Default is to create a private PID namespace for the container
 
 **--pids-limit**=*limit*
 
-Tune the container's pids limit. Set `-1` to have unlimited pids for the container.
+Tune the container's pids limit. Set `0` to have unlimited pids for the container. (default "4096" on systems that support PIDS cgroups).
 
 **--pod**=*name*
 
diff --git a/docs/podman-run.1.md b/docs/podman-run.1.md
index d677f8262..dfc634288 100644
--- a/docs/podman-run.1.md
+++ b/docs/podman-run.1.md
@@ -565,7 +565,7 @@ Default is to create a private PID namespace for the container
 
 **--pids-limit**=*limit*
 
-Tune the container's pids limit. Set `-1` to have unlimited pids for the container.
+Tune the container's pids limit. Set `0` to have unlimited pids for the container. (default "4096" on systems that support PIDS cgroups).
 
 **--pod**=*name*
 
diff --git a/pkg/spec/spec.go b/pkg/spec/spec.go
index c7aa003e8..57c6e8da7 100644
--- a/pkg/spec/spec.go
+++ b/pkg/spec/spec.go
@@ -7,6 +7,7 @@ import (
 	"github.com/containers/libpod/libpod"
 	"github.com/containers/libpod/pkg/cgroups"
 	"github.com/containers/libpod/pkg/rootless"
+	"github.com/containers/libpod/pkg/sysinfo"
 	"github.com/docker/docker/oci/caps"
 	"github.com/docker/go-units"
 	"github.com/opencontainers/runc/libcontainer/user"
@@ -300,9 +301,25 @@ func (config *CreateConfig) createConfigToOCISpec(runtime *libpod.Runtime, userM
 	blockAccessToKernelFilesystems(config, &g)
 
 	// RESOURCES - PIDS
-	if config.Resources.PidsLimit != 0 {
-		g.SetLinuxResourcesPidsLimit(config.Resources.PidsLimit)
-		addedResources = true
+	if config.Resources.PidsLimit > 0 {
+		// if running on rootless on a cgroupv1 machine, pids limit is
+		// not supported.  If the value is still the default
+		// then ignore the settings.  If the caller asked for a
+		// non-default, then try to use it.
+		setPidLimit := true
+		if rootless.IsRootless() {
+			cgroup2, err := cgroups.IsCgroup2UnifiedMode()
+			if err != nil {
+				return nil, err
+			}
+			if !cgroup2 && config.Resources.PidsLimit == sysinfo.GetDefaultPidsLimit() {
+				setPidLimit = false
+			}
+		}
+		if setPidLimit {
+			g.SetLinuxResourcesPidsLimit(config.Resources.PidsLimit)
+			addedResources = true
+		}
 	}
 
 	for name, val := range config.Env {
diff --git a/pkg/sysinfo/sysinfo.go b/pkg/sysinfo/sysinfo.go
index f046de4b1..686f66ce5 100644
--- a/pkg/sysinfo/sysinfo.go
+++ b/pkg/sysinfo/sysinfo.go
@@ -142,3 +142,12 @@ func popcnt(x uint64) (n byte) {
 	x *= 0x0101010101010101
 	return byte(x >> 56)
 }
+
+// GetDefaultPidsLimit returns the default pids limit to run containers with
+func GetDefaultPidsLimit() int64 {
+	sysInfo := New(true)
+	if !sysInfo.PidsLimit {
+		return 0
+	}
+	return 4096
+}
diff --git a/pkg/sysinfo/sysinfo_linux.go b/pkg/sysinfo/sysinfo_linux.go
index 9e675c655..76bda23c6 100644
--- a/pkg/sysinfo/sysinfo_linux.go
+++ b/pkg/sysinfo/sysinfo_linux.go
@@ -7,6 +7,7 @@ import (
 	"path"
 	"strings"
 
+	cg "github.com/containers/libpod/pkg/cgroups"
 	"github.com/opencontainers/runc/libcontainer/cgroups"
 	"github.com/sirupsen/logrus"
 	"golang.org/x/sys/unix"
@@ -227,12 +228,18 @@ func checkCgroupCpusetInfo(cgMounts map[string]string, quiet bool) cgroupCpusetI
 
 // checkCgroupPids reads the pids information from the pids cgroup mount point.
 func checkCgroupPids(quiet bool) cgroupPids {
-	_, err := cgroups.FindCgroupMountpoint("", "pids")
+	cgroup2, err := cg.IsCgroup2UnifiedMode()
 	if err != nil {
-		if !quiet {
-			logrus.Warn(err)
+		logrus.Errorf("Failed to check cgroups version: %v", err)
+	}
+	if !cgroup2 {
+		_, err := cgroups.FindCgroupMountpoint("", "pids")
+		if err != nil {
+			if !quiet {
+				logrus.Warn(err)
+			}
+			return cgroupPids{}
 		}
-		return cgroupPids{}
 	}
 
 	return cgroupPids{