Don't panic when cgroup controller multi-mounted

This commit removes the calls to 'panic' when more than one mount
point for either the cgroupv2 controller or the cgroupv1 memory
controller is found.

It turns out that it is perfectly legal to have a cgroup controller
mounted at multiple points in the filesystem. It is now known that
some Linux security software does exactly this.

[#180668200]

Signed-off-by: Joseph Palermo <jpalermo@pivotal.io>
Co-authored-by: Joseph Palermo <jpalermo@pivotal.io>

sigar_linux.go

@@ -663,7 +663,7 @@ func determineControllerMounts(sysd1, sysd2 *string) {
 
 		if mtype == "cgroup2" {
 			if *sysd2 != "" {
-				panic("Multiple cgroup v2 mount points")
+				return true
 			}
 			*sysd2 = mpath
 			return true
@@ -672,7 +672,7 @@ func determineControllerMounts(sysd1, sysd2 *string) {
 			options := strings.Split(moptions, ",")
 			if stringSliceContains(options, "memory") {
 				if *sysd1 != "" {
-					panic("Multiple cgroup v1 mount points")
+					return true
 				}
 				*sysd1 = mpath
 				return true

sigar_linux_test.go

@@ -147,9 +147,25 @@ memory2 /smart/fox/jumped/by/lazy/dog cgroup2 irrelevant,options
 			})
 		})
 
-		// Note: We cannot test that the system panics when
-		// the file contains multiple entries for any of the
-		// controllers. Because, well, panic.
+		Describe("Multiple Mounts", func() {
+			var sys1, sys2 string
+
+			BeforeEach(func() {
+				setupFile(procd+"/self/mounts", `
+device path type options
+memory1 /somewhere/over/the/rainbow cgroup dummy,memory,and,other
+memory2 /smart/fox/jumped/by/lazy/dog cgroup2 irrelevant,options
+memory1 /somewhere/over/the/rainbow/duplicate cgroup dummy,memory,and,other
+memory2 /smart/fox/jumped/by/lazy/dog/duplicate cgroup2 irrelevant,options
+`)
+			})
+
+			It("it extracts the first matching mounts", func() {
+				determineControllerMounts(&sys1, &sys2)
+				Expect(sys1).To(Equal("/somewhere/over/the/rainbow"))
+				Expect(sys2).To(Equal("/smart/fox/jumped/by/lazy/dog"))
+			})
+		})
 	})
 
 	Describe("CPU", func() {