Subject: bug#53136: 28.0.90; segfault in lock_file

From: Paul Eggert <[email-masked]>
Date: Tue, 11 Jan 2022 18:59:35 -0800

On 1/10/22 17:05, Po Lu wrote:
> Po Lu <[email-masked]> writes:
> 
>> That was an unrelated problem.  This bug is on GNU/Linux, when running
>> under Valgrind.  (I was trying to find the GC bug from last month.)
> 
> It happens with valgrind-3.18.1-7.fc35, but not valgrind-3.17.0-13.fc35.
> 
> Paul, any idea why this may be?  Thanks.

Looking at the 3.18.1 release notes:

https://valgrind.org/docs/manual/dist.news.html

what jumps out at me are these entries:

  * glibc 2.34, which moved various functions from libpthread.so into
    libc.so, is now supported.
  407589  [Linux] Add support for C11 aligned_alloc() and GNU reallocarray()
  442061  very slow execution under Fedora 34 (readdwarf3)

It could be that these changes caused a bug in Valgrind. I think Emacs 
is using aligned_alloc and reallocarray.

I tried building Emacs master (savannah) on both Ubuntu 21.10 x86-64, 
which has valgrind-3.17.0, and on Fedora 35 x86-64, which has 
valgrind-3.18.1, and both instances worked for me. I was running the 
Fedora 35 instance on an AMD Phenom II X4 910e.

I merely stole a lock using an interactive Emacs as my test, though. 
What test are you using to reproduce the bug?