bug#39948: 28.0.50; crash in fchmodat

[Stephen Berman]

On Fri, 06 Mar 2020 16:31:50 +0100 Robert Pluim <rpluim@gmail.com> wrote:

>>>>>> On Fri, 06 Mar 2020 15:16:43 +0100, Stephen Berman
> <stephen.berman@gmx.net> said:
>
>     Stephen> I updated from master today and now Emacs is crashing
>     Stephen> when I use Gnus.  The first time it happened I been
>     Stephen> reading news groups for a while, then email arrived and
>     Stephen> when I pulled it into Gnus, Emacs crashed.  Then I
>     Stephen> restarted Emacs under GDB and now get the crash already
>     Stephen> on starting Gnus (with my initializations; it doesn't
>     Stephen> happen when I start an unconfigured Gnus in Emacs -Q).  I
>     Stephen> tried to get a full backtrace, but the output of `bt
>     Stephen> full' seemed to be in an endless loop; here's the start
>     Stephen> of the backtrace:
>
> Wild Guess: does reverting 07da629926daf849aab248175c88cf53a5e21558
> help? Or maybe 9d626dffc6ba62c0d7a1a5c712f576ed8684fd66 ?

Reverting 07da629 does appear to prevent the crash.  Specifically, as a
sanity check, before reverting, I ran my build from master under GDB
again, started Gnus, but now Emacs didn't crash; however, then I
composed a mail to myself in Gnus and upon sending it, Emacs did crash
exactly as before in fchmodat.  This I did `git revert -n
07da629926daf849aab248175c88cf53a5e21558', rebuilt, started Emacs again,
started Gnus, there was no crash, sent a mail to myself, again with no
crash, and pulled the mail into Gnus also without the crash.  So it
appears that that commit is indeed the cause of the crash.  Thanks for
pinpointing it.

Steve Berman