On Wed, 12 Nov 2008 01:34:54 +0100 (CET)
Jiri Kosina [off-list ref] wrote:

On Wed, 12 Nov 2008, Denys Vlasenko wrote:

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I fully bisected it, and the final "buggy" patch seems to have been 
Denys Vlasenko's patch: cb8f488c33539f096580e202f5438a809195008f (see 
http://github.com/jonsmirl/digispeaker/commit/cb8f488c33539f096580e202f5438a809195008f) 
Denys: Any reason you removed "!prev" in front of "expand_stack"?

Looks like I erroneously thought it can't be NULL,
or that expand_upwards() is ok with getting NULL vma parameter.
I looked again and neither is true.
Sorry, looks like I indeed broke this.

Hmm, so ... ? Seems like this didn't get fixed in Linus' tree yet?

I found my original email in "sent" folder. The patch in that mail does 
NOT remove !prev. That change had beed added by someone else. See 
attached file with original email.
Ok, I think we are not much interested in who did it, 

Hmm, I in fact think we would like to know who removed the check and 
folded it into your original patch. I have added all the Signoffs and CCs 
to the recepient list.

Andrew usually puts

	[someone@somewhere.com: added this and that to the patch]

marker into the changelog, but it's not the case here. 

Having your name in Signed-off-by field of something you are not aware of 
should make you feel at least a little bit nervous IMHO.

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let's fix it for good.
Signed-off-by: Denys Vlasenko <redacted>

--- linux-2.6.28-rc4/mm/mmap.c	Mon Nov 10 01:36:15 2008
+++ linux-2.6.28-rc4.fix/mm/mmap.c	Wed Nov 12 01:21:39 2008

@@ -1704,7 +1704,7 @@
 	vma = find_vma_prev(mm, addr, &prev);
 	if (vma && (vma->vm_start <= addr))
 		return vma;
-	if (expand_stack(prev, addr))
+	if (!prev || expand_stack(prev, addr))
 		return NULL;
 	if (prev->vm_flags & VM_LOCKED) {
 		if (mlock_vma_pages_range(prev, addr, prev->vm_end) < 0)

It looks like this was caused by me fixing rejects.  That was the fancy
include-lots-of-context-so-it-wont-apply patch.