Thanks for filing this! I think that https://crrev.com/c/1349630 (currently in the CQ) should fix it.

https://crrev.com/c/1349630 was first included in 11301.0.0 (per http://crosland/cl?q=1ce26ca7f508347f9a6da55f916570d099225782), but there are still newer failures, e.g. http://stainless/browse/chromeos-autotest-results/262416088-chromeos-test/ (veyron_jerry R72-11314.0.0): "Failed to check /var/run/udev/queue: lstat /var/run/udev/queue: no such file or directory"

I wrote a tiny program to try to reproduce the problem by continually creating and deleting files in a dir in one goroutine and continually calling filepath.Walk on the dir in another goroutine. I receive "no such file or directory" errors (as expected), but I also see that os.IsNotExist returns true (as also expected), so I'm not sure why these would be getting reported in the test.

But in any case, I also see a different error that I think that os.IsNotExist might not ignore, in e.g. http://stainless/browse/chromeos-autotest-results/261950414-chromeos-test/ (lulu R72-11307.0.0): "Failed to check /var/db/pkg/app-text/qpdf-5.1.2-r2: readdirent: input/output error"

I think I'm going to make us ignore all errors reported by filepath.Walk, as I'm worried that we'll get a long tail of weird disk errors from various DUTs otherwise.

Uploaded https://crrev.com/c/1356078.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromiumos/platform/tast-tests/+/e6fda015bde291b064db7486745e97fcd9f5c0c2

commit e6fda015bde291b064db7486745e97fcd9f5c0c2
Author: Daniel Erat <derat@chromium.org>
Date: Fri Nov 30 19:40:34 2018

tast-tests: Make filecheck.Check ignore file-walking errors.

Make filecheck.Check ignore all errors returned by
filepath.Walk. It previously just ignored os.IsNotExist, but
we're also seeing occasional "readdirent: input/output
error" errors when running in the lab.

BUG= chromium:908416 
TEST=ran tests that call filecheck.Check

Change-Id: I7567556871bd57844a6573b0587d3d583cdca539
Reviewed-on: https://chromium-review.googlesource.com/c/1356078
Tested-by: Dan Erat <derat@chromium.org>
Trybot-Ready: Dan Erat <derat@chromium.org>
Reviewed-by: Eric Caruso <ejcaruso@chromium.org>
Reviewed-by: Hidehiko Abe <hidehiko@chromium.org>

[modify] https://crrev.com/e6fda015bde291b064db7486745e97fcd9f5c0c2/src/chromiumos/tast/local/bundles/cros/security/filecheck/filecheck.go