Re: [PATCH,HURD] fix muntrace with mmap-less libio

[Pino Toscano <toscano dot pino at tiscali dot it>]

Alle lunedì 19 novembre 2012, Roland McGrath ha scritto:
> That change is good but it needs a comment.  You don't need to go
> into great detail, just say that we call fprintf+fclose after
> clearing the hooks to match how mtrace called fopen+fprintf before
> setting them.

A bit of comment added.

-- 
Pino Toscano

muntrace: reset file and hooks before finalizing the stream

fclose will call free, invoking its hook, then fprintf which would indirectly
try to allocate a buffer, and this can cause malloc to be used (thus its hook
to be invoked) if libio uses malloc instead of mmap; given any malloc/free hook
locks the internal lock, this leads to a deadlock.

To prevent this hook roundtrip at muntrace, first unset MALLSTREAM and the
hooks, and only after that close the trace file.

2012-11-19  Pino Toscano  <toscano.pino@tiscali.it>

	* malloc/mtrace.c (muntrace): Reset MALLSTREAM and the hooks before
	finalizing MALLSTREAM.
--- a/malloc/mtrace.c
+++ b/malloc/mtrace.c
@@ -361,14 +361,21 @@ mtrace ()
 void
 muntrace ()
 {
+  FILE *f;
+
   if (mallstream == NULL)
     return;
 
-  fprintf (mallstream, "= End\n");
-  fclose (mallstream);
+  /* Do the reverse of what done in mtrace: first reset the hooks and
+     MALLSTREAM, and only after that write the trailer and close the
+     file.  */
+  f = mallstream;
   mallstream = NULL;
   __free_hook = tr_old_free_hook;
   __malloc_hook = tr_old_malloc_hook;
   __realloc_hook = tr_old_realloc_hook;
   __memalign_hook = tr_old_memalign_hook;
+
+  fprintf (f, "= End\n");
+  fclose (f);
 }

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