[LTP] ❌ FAIL: Test report for kernel 5.3.9-rc1-dfe283e.cki (stable)

[Jan Stancek]

----- Original Message -----
> On Mon, Nov 04, 2019 at 10:25:21AM -0500, Jan Stancek wrote:
> > 
> > ----- Original Message -----
> > > On Mon, Nov 04, 2019 at 09:28:10AM -0500, Jan Stancek wrote:
> > > > 
> > > > 
> > > > ----- Original Message -----
> > > > > On Mon, Nov 04, 2019 at 08:35:51AM -0500, Jan Stancek wrote:
> > > > > > 
> > > > > > 
> > > > > > ----- Original Message -----
> > > > > > > 
> > > > > > > Hello,
> > > > > > > 
> > > > > > > We ran automated tests on a recent commit from this kernel tree:
> > > > > > > 
> > > > > > >        Kernel repo:
> > > > > > >        git://git.kernel.org/pub/scm/linux/kernel/git/stable/linux-stable-rc.git
> > > > > > >             Commit: dfe283e9fdac - Linux 5.3.9-rc1
> > > > > > > 
> > > > > > > The results of these automated tests are provided below.
> > > > > > > 
> > > > > > >     Overall result: FAILED (see details below)
> > > > > > >              Merge: OK
> > > > > > >            Compile: OK
> > > > > > >              Tests: FAILED
> > > > > > > 
> > > > > > > All kernel binaries, config files, and logs are available for
> > > > > > > download
> > > > > > > here:
> > > > > > > 
> > > > > > >   https://artifacts.cki-project.org/pipelines/262380
> > > > > > > 
> > > > > > > One or more kernel tests failed:
> > > > > > > 
> > > > > > >     x86_64:
> > > > > > >      ❌ LTP lite
> > > > > > >
> > > > > > 
> > > > > > Not a 5.3 -stable regression.
> > > > > > 
> > > > > > Failure comes from test that sanity checks all /proc files by doing
> > > > > > 1k read from each. There are couple issues it hits wrt. snd_hda_*.
> > > > > > 
> > > > > > Example reproducer:
> > > > > >   dd if=/sys/kernel/debug/regmap/hdaudioC0D3-hdaudio/access
> > > > > >   of=out.txt
> > > > > >   count=1 bs=1024 iflag=nonblock
> > > > > 
> > > > > That's not a proc file :)
> > > > 
> > > > Right. It's same test that's used for /proc too.
> > > > 
> > > > > 
> > > > > > It's slow and triggers soft lockups [1]. And it also requires lot
> > > > > > of memory, triggering OOMs on smaller VMs:
> > > > > > 0x0000000024f0437b-0x000000001a32b1c8 1073745920
> > > > > > seq_read+0x131/0x400
> > > > > > pages=262144 vmalloc vpages N0=262144
> > > > > > 
> > > > > > I'm leaning towards skipping all regmap entries in this test.
> > > > > > Comments are welcomed.
> > > > > 
> > > > > Randomly poking around in debugfs is a sure way to cause crashes and
> > > > > major problems.  Also, debugfs files are NOT stable and only for
> > > > > debugging and should never be enabled on "real" systems.
> > > > > 
> > > > > So what exactly is the test trying to do here?
> > > > 
> > > > It's (unprivileged) user trying to open/read anything it can (/proc,
> > > > /sys)
> > > > to see if that triggers anything bad.
> > > > 
> > > > It can run as privileged user too, which was the case above.
> > > 
> > > Sure, you can do tons of bad things as root poking around in sysfs,
> > > debugfs, and procfs.  What exactly are you trying to do, break the
> > > system?
> > 
> > We are talking about read-only here. Is it unreasonable to expect
> > that root can read all /proc entries without crashing the system?
> 
> You are NOT reading /proc/ here.

No. That was a general question to usefulness of privileged read,
using /proc as example where it commonly happens.

> You are reading debugfs which you
> really have NOT idea what is in there.  As you saw, you are reading from
> hardware that is slow and doing odd things when you read from it.

Agreed, I already sent a patch to LTP to blacklist it.

> And yes, there are some /proc/ files that you should not read from as
> root and expect things to always work.  PCI devices are notorious for
> this, and if you are reading those files as root, you "know" you know
> what you are doing and can accept the risk for when things go wrong.
> 
> It is fine to write tests to read specific /proc/ files that you know
> what is happening in them.  To pick random ones is never a good idea.

Thanks for example.