From: Hugh Dickins <hughd@google.com>
Date: Thu, 13 Sep 2012 00:58:31 +0000 (+1000)
Subject: mm-mmapc-replace-find_vma_prepare-with-clearer-find_vma_links fix
X-Git-Tag: next-20120919~1^2~219
X-Git-Url: https://git.karo-electronics.de/?a=commitdiff_plain;h=3c8aa11cfdf24ff7b73ddf3f69ccbaea99522b7e;p=karo-tx-linux.git

mm-mmapc-replace-find_vma_prepare-with-clearer-find_vma_links fix

Strangely, I can no longer get an uninitialized variable warning out of
copy_vma(), with or without the BUG() there; but David Rientjes gets it
when he builds with CONFIG_BUG off, which is understandable.

uninitialized_var() can be a useful tool, but I do prefer to avoid it:
partly because it might hide future errors, partly because I misspell it,
but mainly because the need for it comes and goes so mysteriously.

Given David's preference for no warning, mine for no uninitialized_var,
and Linus's for renaming BUG() to I_AM_A_MORON() to discourage its use in
the first place: copy_vma() seems a prime candidate for returning failure
to mremap instead of crashing the system.

Signed-off-by: Hugh Dickins <hughd@google.com>
Cc: Benny Halevy <bhalevy@tonian.com>
Cc: Hillf Danton <dhillf@gmail.com>
Cc: David Rientjes <rientjes@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

diff --git a/mm/mmap.c b/mm/mmap.c
index 07ae3776866b..7f408ab38f72 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -2352,7 +2352,7 @@ struct vm_area_struct *copy_vma(struct vm_area_struct **vmap,
 	}
 
 	if (find_vma_links(mm, addr, addr + len, &prev, &rb_link, &rb_parent))
-		BUG();
+		return NULL;	/* should never get here */
 	new_vma = vma_merge(mm, prev, addr, addr + len, vma->vm_flags,
 			vma->anon_vma, vma->vm_file, pgoff, vma_policy(vma));
 	if (new_vma) {