bug#41321: 27.0.91; Emacs aborts due to invalid pseudovector objects

[Pip Cet]

On Sat, May 16, 2020 at 10:34 AM Eli Zaretskii <eliz@gnu.org> wrote:
> So far, I've seen this in a C Mode buffer reverted because "git pull"
> brought a modified version, and in an Info mode buffer reverted
> because the manual was rebuilt after the Texinfo sources were
> modified.  In the latter case I captured a backtrace, see below.
>
> The problem seem to involve invalid markers, perhaps markers that were
> unchained and put on the free list

Even unchained markers shouldn't be put on the free list as long as
they're still reachable, so I suspect the problem is more likely to be
caused by that.

> (witness the PVEC_FREE object that
> caused the abort in the backtrace below, where Emacs seems to be
> trying to display an error message about an invalid marker).

What I would do next is run with a breakpoint on wrong_type_argument
(if that's impossible, change the code in CHECK_MARKER to abort upon
encountering a PVEC_FREE vector) to see where the reference to the
freed pseudovector came from. An undo list, maybe?