From: Rusty Russell <rusty@rustcorp.com.au>
Date: Tue, 17 Jul 2012 19:27:31 +0000 (+0930)
Subject: talloc_stack: report lazy freeing (panic if DEVELOPER).
X-Git-Url: http://git.samba.org/?p=obnox%2Fsamba%2Fsamba-obnox.git;a=commitdiff_plain;h=84fb37fe372bc22e0a3ceca8030bff459225044a

talloc_stack: report lazy freeing (panic if DEVELOPER).

talloc_stackframe() stacks, so if you forget to free one, the outer
one will free it.  However, it's not a good idea to rely too heavily
on this behaviour: it can lead to delays in the release of memory or
destructors.

I had an elaborate hack to make sure every talloc_stackframe() was
freed in the exact same function it was allocated, however all bugs it
caught were simply lazy freeing, so this patch just checks for that.

This doesn't check for stackframes we don't free up on exit: that would
be nice, but uncovers some uncomfortable (but probably harmless) cases.

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
---

diff --git a/lib/util/talloc_stack.c b/lib/util/talloc_stack.c
index 304ea17d8c4..be332af571b 100644
--- a/lib/util/talloc_stack.c
+++ b/lib/util/talloc_stack.c
@@ -96,6 +96,17 @@ static int talloc_pop(TALLOC_CTX *frame)
 		(struct talloc_stackframe *)SMB_THREAD_GET_TLS(global_ts);
 	int i;
 
+	/* Catch lazy frame-freeing. */
+	if (ts->talloc_stack[ts->talloc_stacksize-1] != frame) {
+		DEBUG(0, ("Freed frame %s, expected %s.\n",
+			  talloc_get_name(frame),
+			  talloc_get_name(ts->talloc_stack
+					  [ts->talloc_stacksize-1])));
+#ifdef DEVELOPER
+		smb_panic("Frame not freed in order.");
+#endif
+	}
+
 	for (i=ts->talloc_stacksize-1; i>0; i--) {
 		if (frame == ts->talloc_stack[i]) {
 			break;