segfault when running with memory limit but without swap limit

[afbjorklund]

Is this a BUG REPORT or FEATURE REQUEST? (leave only one on its own line)

/kind bug

Description

Explicitly removing swap limit causes a segmentation fault.

Steps to reproduce the issue:

1. sudo podman run --memory 256m --memory-swap -1 busybox true

Describe the results you received:

panic: runtime error: invalid memory address or nil pointer dereference

Describe the results you expected:

Additional information you deem important (e.g. issue happens only occasionally):

Output of podman version:

podman version 3.0.0

Output of podman info --debug:

(paste your output here)

Package info (e.g. output of rpm -q podman or apt list podman):

(paste your output here)

Have you tested with the latest version of Podman and have you checked the Podman Troubleshooting Guide?

No

Additional environment details (AWS, VirtualBox, physical, etc.):

Ubuntu 20.04

---

These are supposed to be equivalent:

$ sudo podman run --memory 256m busybox true
Your kernel does not support swap limit capabilities or the cgroup is not mounted. Memory limited without swap.
$ sudo podman run --memory 256m --memory-swap -1 busybox true
panic: runtime error: invalid memory address or nil pointer dereference
[signal SIGSEGV: segmentation violation code=0x1 addr=0x0 pc=0x15ee61e]

goroutine 1 [running]:
github.com/containers/podman/v2/cmd/podman/common.getMemoryLimits(0xc00034ec00, 0x27d8da0, 0x1b05550, 0x17, 0xc0005bc508)
	cmd/podman/common/specgen.go:153 +0x33e
github.com/containers/podman/v2/cmd/podman/common.FillOutSpecGen(0xc00034ec00, 0x27d8da0, 0xc000139600, 0x4, 0x8, 0x0, 0x18ab660)
	cmd/podman/common/specgen.go:430 +0xda6
github.com/containers/podman/v2/cmd/podman/containers.run(0x2748b80, 0xc000139600, 0x4, 0x8, 0x0, 0x0)
	cmd/podman/containers/run.go:171 +0x46f
github.com/spf13/cobra.(*Command).execute(0x2748b80, 0xc00003c0c0, 0x8, 0x8, 0x2748b80, 0xc00003c0c0)
	vendor/github.com/spf13/cobra/command.go:850 +0x47c
github.com/spf13/cobra.(*Command).ExecuteC(0x275c140, 0xc000044088, 0x18d6c80, 0x280b340)
	vendor/github.com/spf13/cobra/command.go:958 +0x375
github.com/spf13/cobra.(*Command).Execute(...)
	vendor/github.com/spf13/cobra/command.go:895
github.com/spf13/cobra.(*Command).ExecuteContext(...)
	vendor/github.com/spf13/cobra/command.go:888
main.Execute()
	cmd/podman/root.go:92 +0xec
main.main()
	cmd/podman/main.go:36 +0x92

System doesn't have "cgroup_enable=memory swapaccount=1" cmdline