Emacs hang (100%CPU) on saving a root-owned + r/o file

[David Reitter]

This was reported by an Aquamacs user.

I can reliably reproduce this with various recent CVS builds with -Q  
(Carbon port on OS X).
I stopped it with C-g, the stack trace is below.

---
Alastair Rankine:
http://sourceforge.net/tracker/index.php? 
func=detail&aid=1362636&group_id=138078&atid=740475

100% CPU when attempting to save a file owned by root
To reproduce:

1. Open a file that is owned by root (eg
/etc/httpd/httpd.conf)
2. type ^x^q to toggle readonly mode
3. Make a trivial change
4. Save
5. Answer y to the prompt "file x is write-protected;
try to save anyway? (y or n)"

Emacs goes into 100% CPU usage.

Enclosed is a sample of the app when it is in this
state, courtesy of the Activity Monitor. (recursive
call to mark_object?)

This is with "bare" Aquamacs 0.9.6, no customization
file, no init file.


=====


Debugger entered--Lisp error: (quit)
  copy-file("/etc/httpd/httpd.conf" "/etc/httpd/httpd.conf~" t t excl)
  byte-code("¬√ƒè?	∆?%?á" [from-name to-name nil (delete-file to- 
name) ((file-error)) copy-file t excl] 6)
  backup-buffer-copy("/etc/httpd/httpd.conf" "/etc/httpd/ 
httpd.conf~" 420)
  byte-code("Ñc   Ñc\nÉ∆«\n»\"WÑc… !!Éc\fÉ)À!ÃVÑc
Ñ3®ÉmÕ!
ÑTŒ8®Ö_®Ö_Œ8XÖ_œ8Ü_–!?)Ém—\n#àÇz“”#à\nB∆á" [file- 
precious-flag backup-by-copying modes real-file-name backup-by- 
copying-when-linked backup-by-copying-when-mismatch 0 logand 3072  
file-writable-p file-name-directory file-nlinks 1 file-attributes 2 9  
file-ownership-preserved-p backup-buffer-copy rename-file t backup-by- 
copying-when-privileged-mismatch attr backupname setmodes] 4)
  byte-code("Ö	∆=Ñ	«=Ö	Ü»… \n\"!À!«ÃÕè?	 
É:É:«ŒœèàAâÑ.*á" [targets delete-old-versions real-file-name  
buffer-file-name modes buffer-backed-up t nil y-or-n-p format "Delete  
excess backup versions of %s? " file-modes (byte-code "Ñc	Ñc 
\nÉ∆«\n»\"WÑc… !!Éc\fÉ)À!ÃVÑc
Ñ3®ÉmÕ!
ÑTŒ8®Ö_®Ö_Œ8XÖ_œ8Ü_–!?)Ém—\n#àÇz“”#à\nB∆á" [file- 
precious-flag backup-by-copying modes real-file-name backup-by- 
copying-when-linked backup-by-copying-when-mismatch 0 logand 3072  
file-writable-p file-name-directory file-nlinks 1 file-attributes 2 9  
file-ownership-preserved-p backup-buffer-copy rename-file t backup-by- 
copying-when-privileged-mismatch attr backupname setmodes] 4) ((file- 
error ...)) (byte-code "address@hidden" [targets delete-file] 2) ((file- 
error)) setmodes] 5)
  backup-buffer()
  basic-save-buffer-2()
  basic-save-buffer-1()
  basic-save-buffer()
  save-buffer(1)
  call-interactively(save-buffer)

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