Re: [CFT][PATCH 09/10] sysfs: Create mountpoints with sysfs_create_empty_dir

Tejun Heo [off-list ref] writes:

Hey,

On Tue, Aug 11, 2015 at 2:57 PM, Eric W. Biederman
[off-list ref] wrote:

quoted

quoted

So, this somehow ends up confusing upstart on centos6 based systems
making it fail to mount tmpfs on /sys/fs/cgroup.  It also skips sunrpc
and other mounts are different too.  No idea why at this point.  Can
we please revert this from -stable until we know what's going on?

*Boggle*

The only time this should prevent anything is when in a container when
you are not global root.  And then only mounting sysfs should be
affected.

This is just plain boot. No namespace involved.

quoted

The only difference in executed code really should be setting an extra
flag on the kernfs, inode.  The kernfs changes will also refuse to add
entries to these directories (but these directories are empty).

Why do we have this in -stable then? Is this part of a larger fix?

It is. This patch is part of the prep work to prevent unprivileged users
not mounting sysfs (using user namespace permissions) when they should
not be allowed to.

quoted

If this is causing problems I don't have a problem with a revert but
reverts take a minute, and this seems to be the first report of this
kind.  Can we take a minute and attempt to get a coherent explanation.

It should be a matter of moments to debug this
issue (once a test environment is setup), and see what is wrong and then
we can act intelligently.  Tracing a single system call is not difficult.

I'm already out today so it'll have to wait till tomorrow.

quoted

If there really is some weird issue I want to know what it is.

Sure, but you wanna do that in -stable?

Before fixing anything I want a bug report that is clear enough
to be reproducible.

I just went and attempted to reproduce this, and on RHEL6 workstation
(aka my work laptop), using the todays 4.2.0-rc6+ aka
edf15b4d4b01b565cb5f4fd2e2d08940b9f92e2f and all of the mounts in
/proc/self/mounts are the same between 4.2.0-rc6 and the RHEL6 stock
2.6.32-504.30.3.el6.x86_64, including the cgroups mounted on /cgroup.

Which means that I don't have any reason to believe that normal CentOS 6
is broken.

Which -stable kernel are you having problems with?  Perhaps it was
a broken backport?

Is it possible this is a local CentOS 6 hack that is breaking?
Perhaps a patch you apply on top of your -stable kernel?

Certainly with cgroups expected to be mounted at /sys/fs/cgroup there
has clearly been at least one change from the stock configuration.

I think it is a little less serious if stock CentOS 6 doesn't have
problems.  Unless it is a conflict of kernel patches I definitely think
whatever it is needs to be fixed.

Eric