[PATCH] emacs: Fix stack overflow in notmuch-wash-tidy-citations

[PATCH] emacs: Fix stack overflow in notmuch-wash-tidy-citations

[Michal Sojka]

The following message (146 kB) breaks the emacs interface:
http://rtime.felk.cvut.cz/~sojka/notmuch/notmuch-wash-tidy-citations-stack-overflow.txt

An attempt to view the message produced message
"notmuch-wash-tidy-citations: Stack overflow in regexp matcherq" and
it was not possible to work with the message.

I tracked the problem down to the regexp search, which probably
attempts to match a very big piece of text (several lines). I changed
the regexp to only match a single line. The result is probably slower,
but doesn't produce the error.
---
 emacs/notmuch-wash.el |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)

diff --git a/emacs/notmuch-wash.el b/emacs/notmuch-wash.el
index 26a3f88..051dd17 100644
--- a/emacs/notmuch-wash.el
+++ b/emacs/notmuch-wash.el
@@ -218,7 +218,7 @@ Perform four transformations on the message body:
 
   ;; Insert a blank line before a citation if there isn't one.
   (goto-char (point-min))
-  (while (re-search-forward "\\(^[^>]+\\)\n>" nil t)
+  (while (re-search-forward "\\(^[^>][^\n]+\\)\n>" nil t)
     (replace-match "\\1\n\n>"))
 
   ;; Insert a blank line after a citation if there isn't one.
-- 
1.7.1.3.g75e44

Re: [PATCH] emacs: Fix stack overflow in notmuch-wash-tidy-citations

[Dmitry Kurochkin]

Hi Michal.

On Fri, 16 Jul 2010 13:32:35 +0200, Michal Sojka <sojkam1@fel.cvut.cz> wrote:
> The following message (146 kB) breaks the emacs interface:
> http://rtime.felk.cvut.cz/~sojka/notmuch/notmuch-wash-tidy-citations-stack-overflow.txt
> 
> An attempt to view the message produced message
> "notmuch-wash-tidy-citations: Stack overflow in regexp matcherq" and
> it was not possible to work with the message.
> 
> I tracked the problem down to the regexp search, which probably
> attempts to match a very big piece of text (several lines). I changed
> the regexp to only match a single line. The result is probably slower,
> but doesn't produce the error.

I have 2 messages that cause emacs segfault. Both are notifications from
svn. One is 37933 lines, 1,2M. Another is huge - 963179 lines, 31M. I
believe the root cause is the same for both segfaults.

Your patch does not fix the problem, unfortunately. Can you advise how
to debug this segfault? Build emacs with debug symbols and get backtrace
from gdb? Debug notmuch lisp code (how?)? Enable some verbose logging in
emacs?

Regards,
  Dmitry

> ---
>  emacs/notmuch-wash.el |    2 +-
>  1 files changed, 1 insertions(+), 1 deletions(-)
> 
> diff --git a/emacs/notmuch-wash.el b/emacs/notmuch-wash.el
> index 26a3f88..051dd17 100644
> --- a/emacs/notmuch-wash.el
> +++ b/emacs/notmuch-wash.el
> @@ -218,7 +218,7 @@ Perform four transformations on the message body:
>  
>    ;; Insert a blank line before a citation if there isn't one.
>    (goto-char (point-min))
> -  (while (re-search-forward "\\(^[^>]+\\)\n>" nil t)
> +  (while (re-search-forward "\\(^[^>][^\n]+\\)\n>" nil t)
>      (replace-match "\\1\n\n>"))
>  
>    ;; Insert a blank line after a citation if there isn't one.
> -- 
> 1.7.1.3.g75e44
> 
> _______________________________________________
> notmuch mailing list
> notmuch@notmuchmail.org
> http://notmuchmail.org/mailman/listinfo/notmuch

Re: [PATCH] emacs: Fix stack overflow in notmuch-wash-tidy-citations

[Michal Sojka]

Hi Dmitry,

On Sat, 17 Jul 2010, Dmitry Kurochkin wrote:
> I have 2 messages that cause emacs segfault.

My patch didn't fix a segfault but stack overflow which was reported by
emacs in its *Messages* buffer without crashing.

> Both are notifications from svn. One is 37933 lines, 1,2M. Another is
> huge - 963179 lines, 31M. I believe the root cause is the same for
> both segfaults.
> 
> Your patch does not fix the problem, unfortunately. Can you advise how
> to debug this segfault? Build emacs with debug symbols and get backtrace
> from gdb?

I'm more Emacs user then developer so I cannot give you much detailed
information. First, try to check
http://mid.gmane.org/87pr0t5h1q.fsf@yoom.home.cworth.org and Emacs
bug#6214. There may by a fix your problem.


> Debug notmuch lisp code (how?)? Enable some verbose logging in emacs?

To debug elisp code I open the source in Emacs, move the point to the
function I'm interested in and press C-u C-M-x. This instruments the
function code so that the next time the function is invoked, elisp
debugger appears and you can execute the function step by step and
inspect variables.

Maybe, some Emacs guru can give you a better advice.

Bye
Michal