From: Eli Zaretskii <eliz@gnu.org>
To: Pip Cet <pipcet@gmail.com>, Daniel Colascione <dancol@dancol.org>
Cc: emacs-devel@gnu.org
Subject: Failing to GC killed buffers considered harmful
Date: Sun, 29 Mar 2020 17:23:02 +0300 [thread overview]
Message-ID: <838sjj5jg9.fsf@gnu.org> (raw)
This recent change on master:
commit afaf2f465188ab1f438ff3e021260e7c529b1b9d
Author: Pip Cet <pipcet@gmail.com>
AuthorDate: Sat Mar 14 18:26:33 2020 +0000
Commit: Eli Zaretskii <eliz@gnu.org>
CommitDate: Sun Mar 15 16:35:07 2020 +0200
Make sure we mark reachable killed buffers during GC
* src/alloc.c (live_buffer_holding): Add ALL_BUFFERS argument for
returning killed buffers.
(mark_maybe_object, mark_maybe_pointer): Use the additional
argument. (Bug#39962)
causes us to dump killed buffers in some cases. Presumably, the call
to GC right before we start pdumping fails to collect a killed buffer,
and it ends up being dumped. When we restore from emacs.pdump, an
Emacs built with --enable-checking on a platform that uses mmap for
buffer text aborts here:
#ifdef USE_MMAP_FOR_BUFFERS
if (dumped_with_unexec_p ())
{
...
}
else
{
struct buffer *b;
/* Only buffers with allocated buffer text should be present at
this point in temacs. */
FOR_EACH_BUFFER (b)
{
eassert (b->text->beg != NULL); <<<<<<<<<<<<<<<<<
}
}
#endif /* USE_MMAP_FOR_BUFFERS */
because a killed buffer has its text freed and set to NULL.
We could, of course, remove the assertion, but then we are left with a
dead buffer that will never be GC'ed, AFAIU, because objects that come
from the portable dump are considered constantly marked.
Another idea is to avoid dumping such buffers. But I couldn't find a
facility for doing that safely; simply having dump_buffer return
causes an assertion violation later:
#ifdef ENABLE_CHECKING
static Lisp_Object
dump_check_overlap_dump_reloc (Lisp_Object lreloc_a,
Lisp_Object lreloc_b)
{
struct dump_reloc reloc_a = dump_decode_dump_reloc (lreloc_a);
struct dump_reloc reloc_b = dump_decode_dump_reloc (lreloc_b);
eassert (dump_reloc_get_offset (reloc_a) < dump_reloc_get_offset (reloc_b));
return Qnil;
}
#endif
Daniel, did I miss some facility to avoid dumping an object safely?
If not, what other solutions could we try, given that whether some
pointer into a buffer ends up on the stack at pdump time is something
we cannot really control?
TIA
next reply other threads:[~2020-03-29 14:23 UTC|newest]
Thread overview: 26+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-03-29 14:23 Eli Zaretskii [this message]
2020-03-29 16:45 ` Failing to GC killed buffers considered harmful Stefan Monnier
2020-03-29 18:54 ` Eli Zaretskii
2020-03-29 19:06 ` Daniel Colascione
2020-03-29 19:24 ` Eli Zaretskii
2020-03-29 16:46 ` Pip Cet
2020-03-29 18:48 ` Eli Zaretskii
2020-03-29 19:07 ` Pip Cet
2020-03-29 19:12 ` Daniel Colascione
2020-03-29 19:25 ` Pip Cet
2020-03-29 19:28 ` Eli Zaretskii
2020-03-30 15:36 ` Pip Cet
2020-03-30 15:53 ` dancol
2020-03-30 17:07 ` Stefan Monnier
2020-03-30 17:02 ` Stefan Monnier
2020-03-30 18:32 ` Stefan Monnier
2020-03-30 18:51 ` Eli Zaretskii
2020-03-30 19:14 ` Daniel Colascione
2020-03-30 19:40 ` Stefan Monnier
2020-03-31 14:07 ` Eli Zaretskii
2020-03-31 14:09 ` Eli Zaretskii
2020-03-31 21:57 ` Stefan Monnier
2020-03-31 14:58 ` Pip Cet
2020-03-31 16:52 ` Stefan Monnier
2020-03-31 18:23 ` Pip Cet
2020-03-31 19:20 ` Stefan Monnier
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