[Bug 2047450] Re: tail emits no output for sysfs files when using large page kernels

[Timo Aaltonen]

Hello dann, or anyone else affected,

Accepted coreutils into mantic-proposed. The package will build now and
be available at
https://launchpad.net/ubuntu/+source/coreutils/9.1-1ubuntu2.23.10.1 in a
few hours, and then in the -proposed repository.

Please help us by testing this new package.  See
https://wiki.ubuntu.com/Testing/EnableProposed for documentation on how
to enable and use -proposed.  Your feedback will aid us getting this
update out to other Ubuntu users.

If this package fixes the bug for you, please add a comment to this bug,
mentioning the version of the package you tested, what testing has been
performed on the package and change the tag from verification-needed-
mantic to verification-done-mantic. If it does not fix the bug for you,
please add a comment stating that, and change the tag to verification-
failed-mantic. In either case, without details of your testing we will
not be able to proceed.

Further information regarding the verification process can be found at
https://wiki.ubuntu.com/QATeam/PerformingSRUVerification .  Thank you in
advance for helping!

N.B. The updated package will be released to -updates after the bug(s)
fixed by this package have been verified and the package has been in
-proposed for a minimum of 7 days.

** Changed in: coreutils (Ubuntu Mantic)
       Status: In Progress => Fix Committed

** Tags added: verification-needed verification-needed-mantic

** Changed in: coreutils (Ubuntu Jammy)
       Status: In Progress => Fix Committed

** Tags added: verification-needed-jammy

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https://bugs.launchpad.net/bugs/2047450

Title:
  tail emits no output for sysfs files when using large page kernels

Status in coreutils package in Ubuntu:
  Fix Released
Status in coreutils source package in Jammy:
  Fix Committed
Status in coreutils source package in Lunar:
  Won't Fix
Status in coreutils source package in Mantic:
  Fix Committed
Status in coreutils source package in Noble:
  Fix Released

Bug description:
  [Impact]
  Ubuntu provides 64K page size kernels for ppc64el (always) and arm64 (optional -64k flavors). When booted on 64K kernels, tail emits no output when tailing a sysfs file. The difference in behavior can be a source for bugs in scripts that use tail, and general user confusion.

  [Test Plan]
  The upstream fix includes a test case that tails the /sys/kernel/profiling file, if it exists. That case would fail with an unfixed coreutils package as shown below:

  = When booted on a 4K kernel =
  ubuntu at gunyolk:~$ tail /sys/kernel/profiling 
  0

  = When booted on a 64K kernel =
  ubuntu at gunyolk:~$ tail /sys/kernel/profiling 
  ubuntu at gunyolk:~$ 

  Since the upstream test cases are executed at build time, the existing
  tests and this new test will be used  to regression test behavior.
  This should cover both 4K (!ppc64el) and 64K (ppc64el) cases. We
  should also do a manual verification on arm64 w/ the 64K kernel since
  that case is not covered by our builders.

  [Where Problems Could Occur]
  The biggest risk for a regression I see is due to the side-effect of the fix now allocating a dynamic buffer instead of the stack. An error in logic there could cause a crash or a memory leak in scenarios undetected during testing. I used valgrind when developing the fix to derisk the memory leak scenario.

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