[Bug 2146842] Re: tcmalloc RSEQ ABI violation causes crashes on linux kernel 6.19+

[Christian Ehrhardt]

Thanks for the further checks Lena!

With that tested and confirmed I think we can rest assured about general
Archive breakage - as there is none to be had so far except if there is
a hidden RSEQ user we missed to look at.

And the really affected library (full tcmalloc) isn't shipped in Ubuntu
either.

For general awareness we might mention it in the release notes still,
but I'd not see the messaging as a regression because as it seems all it
did was getting stricter on an API - so it isn't really a bug (We can
leave the discussion between kernel and tcmalloc to them).

OTOH the kernel changes thousands of things every time and what is in
the archive we try to smoothen and hold compatible. But we do not list
all potential and theoretical things out there that could have issues.
The only difference here is that it was brought to our attention. But
the kernel did nothing wrong nor is something in the Ubuntu archive
affected.

I'm unsure but IMHO this thereby would come down
a) do nothing
b) to a kernel related release note entry like "FYI Kernel got stricter, nothing in the archive is affected, but if you use code relying on that wrong behavior you might see issues - known is for example this issue in tcmalloc [link]"
WDYT?

At least this is clearly less urgent or widespread of a problem than it first looked.
Let us talk about the next steos next time we meet.

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https://bugs.launchpad.net/bugs/2146842

Title:
  tcmalloc RSEQ ABI violation causes crashes on linux kernel 6.19+

Status in Google Perftools Packaging:
  New
Status in google-perftools package in Ubuntu:
  Invalid

Bug description:
  With the 6.19 release of the Linux kernel, upstream MongoDB now
  experiences crashes after ~30 seconds due to an RSEQ error from
  tcmalloc. The unit test
  //tcmalloc/testing:background_test_no_glibc_rseq notably also fails on
  6.19 and 7.0, and may be due to the following commit -
  https://lore.kernel.org/all/20251027084307.578058898@linutronix.de/

  While mongodb is not supported in the Ubuntu archive, there are other
  packages using tcmalloc such as mysql-8.4 which may be affected.

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