canary-on-1.16 block tests flaky

[msau42]

https://k8s-testgrid.appspot.com/sig-storage-csi-ci#canary-on-1.16

Oddly enough, canary-on-master tests seem fine.

@jsafrane @pohly could you help take a look?

/kind failing-test

[msau42]

Its flaky across all jobs, not just this.

I think it's related to running on kind, where hostpath volumes go to the host. There may be races due another test grabbing the same device

[msau42]

Although if that were the case, then intree parallel tests should be flaky too? Maybe it's a probability game since there a lot more tests running intree

[pohly]

There may be races due another test grabbing the same device

Creating a loop device is done by kubelet and the CSI hostpath driver with https://github.com/kubernetes/kubernetes/blob/8a09460c2f7ba8f6acd8a6fb7603ed3ac4805eb6/pkg/volume/util/volumepathhandler/volume_path_handler_linux.go#L96-L112.

The command invocation itself (= "losetup -f --show") shouldn't be racy. Let's look at its implementation:

openat(AT_FDCWD, "/dev/loop-control", O_RDWR|O_CLOEXEC) = 3
ioctl(3, LOOP_CTL_GET_FREE)             = 0
close(3)                                = 0
lstat("/tmp", {st_mode=S_IFDIR|S_ISVTX|0777, st_size=260, ...}) = 0
lstat("/tmp/test", {st_mode=S_IFREG|0644, st_size=1073741824, ...}) = 0
openat(AT_FDCWD, "/tmp/test", O_RDWR|O_CLOEXEC) = 3
openat(AT_FDCWD, "/dev/loop0", O_RDWR|O_CLOEXEC) = 4
ioctl(4, LOOP_SET_FD, 3)                = 0
ioctl(4, LOOP_SET_STATUS64, {lo_offset=0, lo_number=0, lo_flags=0, lo_file_name="/tmp/test", ...}) = 0

losetup first determines the next available loop device, then opens it and configures it. At first glance this looks like it might be racy, but that depends on how LOOP_SET_FD and losetup behave when someone else grabs the device in parallel.

I tested that by running losetup under gdb and pausing it in the LOOP_SET_FD ioctl, then taking the loop device with some other losetup call. The first invocation recovered gracefully from that by retrying with another loop device.

So my conclusion is that we don't have a race around loop device creation.

Perhaps KinD containers have the same issue that we also had in the CSI hostpath container where /dev is a static copy of the host and then new loop devices don't show up?

https://github.com/kubernetes/kubernetes/blob/8a09460c2f7ba8f6acd8a6fb7603ed3ac4805eb6/pkg/volume/util/volumepathhandler/volume_path_handler_linux.go#L96-L112

Indeed, when I just ran the CSI hostpath prow tests on my development machine after using all existing loop devices, the blockvolume tests fail because losetup fails:

Jan 13 08:31:51.654: INFO: At 2020-01-13 08:27:28 +0100 CET - event for security-context-6ade56c3-0fd9-4080-a3b5-e46a57584a4c: {kubelet csi-prow-worker} FailedMapVolume: MapVolume.AttachFileDevice failed for volume "pvc-228ac164-bec1-43fe-a3d1-7671ef0549f6" : exit status 1

I've not found more about it in the logs, but I can reproduce the problem manually by creating loop devices with docker exec f049e80f378a sh -c 'truncate -s 1G /tmp/testfile; losetup -f --show /tmp/testfile' until eventually all the ones that existed when the KinD container was started are in use and the command fails with:

losetup: /tmp/testfile: failed to set up loop device: No such file or directory

I'll file an issue against KinD.

[pohly]

I'll file an issue against KinD.

=> kubernetes-sigs/kind#1248

[fejta-bot]

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[msau42]

/close

[k8s-ci-robot]

@msau42: Closing this issue.

In response to this:

/close

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