[Bug 1864864] Re: [SRU] pthread_rwlock_trywrlock results in hang

[Andreas Hasenack]

Can someone who is affected by this bug, and able to reproduce it in a
test/controlled environment, please try the glibc packages from my PPA?
Note you will have to restart services after the update (or better yet,
reboot if you can):

https://launchpad.net/~ahasenack/+archive/ubuntu/glibc-pthread-
lock-1864864

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https://bugs.launchpad.net/bugs/1864864

Title:
  [SRU] pthread_rwlock_trywrlock results in hang

Status in glibc package in Ubuntu:
  Fix Released
Status in glibc source package in Bionic:
  Triaged
Status in glibc package in Debian:
  Fix Released

Bug description:
  [Impact]

   * pthread_rwlock_trywrlock and pthread_rwlock_tryrdlock before glibc
  2.30 could hang:
  https://sourceware.org/bugzilla/show_bug.cgi?id=23844#c14

   * We are especially able to reproduce the problem with BIND 9.16.x
  when --with-pthread-rwlock configure option enabled

   * But the impact is not limited to BIND 9.16, but any multithreaded
  application using phtread rwlocks

  [Test Case]

  * Fetch the source program and build it:
  $ wget https://bugs.launchpad.net/ubuntu/+source/glibc/+bug/1864864/+attachment/5333068/+files/bug23844.wr.c
  $ gcc bug23844.wr.c -lpthread -o bug23844wr

  * Run the resulting binary a few times. On affected systems, it should
  hang in less then 10 attempts.

  $ ./bug23844rw
  trylock_wr
  500000

  (...)

  $ ./bug23844.wr
  trylock_wr
  <hangs>

  [Regression Potential]

   * The upstream fix has been in glibc 2.30 and later
   * Debian has the fix in 2.28-8 as part of "git-updates.diff" from February 2019

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