linux-kernel - Re: [PATCH 0/5] kmod/umh: a few fixes

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Date:   Fri, 19 Jun 2020 20:46:26 +0000
From:   Luis Chamberlain <mcgrof@...nel.org>
To:     unlisted-recipients:; (no To-header on input)
Cc:     gregkh@...uxfoundation.org, viro@...iv.linux.org.uk,
        philipp.reisner@...bit.com, lars.ellenberg@...bit.com,
        axboe@...nel.dk, roopa@...ulusnetworks.com,
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        linux-fsdevel@...r.kernel.org, bridge@...ts.linux-foundation.org,
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Subject: Re: [PATCH 0/5] kmod/umh: a few fixes

On Wed, Jun 17, 2020 at 05:43:48PM -0700, Andrew Morton wrote:
> On Wed, 10 Jun 2020 15:49:18 +0000 "Luis R. Rodriguez" <mcgrof@...nel.org> wrote:
> 
> > Tiezhu Yang had sent out a patch set with a slew of kmod selftest
> > fixes, and one patch which modified kmod to return 254 when a module
> > was not found. This opened up pandora's box about why that was being
> > used for and low and behold its because when UMH_WAIT_PROC is used
> > we call a kernel_wait4() call but have never unwrapped the error code.
> > The commit log for that fix details the rationale for the approach
> > taken. I'd appreciate some review on that, in particular nfs folks
> > as it seems a case was never really hit before.
> > 
> > This goes boot tested, selftested with kmod, and 0-day gives its
> > build blessings.
> 
> Any thoughts on which kernel version(s) need some/all of these fixes?

Well, in so far as fixes, this is the real important part:

* request_module() used to fail with an error code of
  256 when a module was not found. Now it properly
  returns 1.

* fs/nfsd/nfs4recover.c: we never were disabling the
  upcall as the error code of -ENOENT or -EACCES was
  *never* properly checked for error code

Since the request_module() fix is only affecting userspace
for the kmod tests, through the kmod test driver, ie, we don't expose
this to userspace in any other place, I don't see that as critical.
Let me be clear, we have a test_kmod driver which exposes knobs
and one of the knobs lets userspace query the return value of a
request_module() call, and we use this test_kmod driver to stress
test kmod loader. Let us also recall that the fix is *iff* an error
*did* occur. I *cannot* think of a reason why this would be critical
to merge to older stable kernels for this reason for request_module()'s
sake.

Bruce, Chuck:

But... for NFS... I'd like the NFS folks to really look at that
and tell us is some folks really should care about that. I also
find it perplexing there was a comment in place there to *ensure*
the error was checked for, and so it seemed someone cared for that
condition.

> >  drivers/block/drbd/drbd_nl.c         | 20 +++++------
> >  fs/nfsd/nfs4recover.c                |  2 +-
> >  include/linux/sched/task.h           | 13 ++++++++
> >  kernel/kmod.c                        |  5 ++-
> >  kernel/umh.c                         |  4 +--
> >  lib/test_kmod.c                      |  2 +-
> >  net/bridge/br_stp_if.c               | 10 ++----
> >  security/keys/request_key.c          |  2 +-
> >  tools/testing/selftests/kmod/kmod.sh | 50 +++++++++++++++++++++++-----
> 
> I'm not really sure who takes kmod changes - I'll grab these unless
> someone shouts at me.

Greg usually takes it, but as usual, thanks for picking up the slack ;)

  Luis