From: Christoph Lameter <clameter@engr.sgi.com>
Date: Sun, 5 Feb 2006 07:27:55 +0000 (-0800)
Subject: [PATCH] hugetlb: add comment explaining reasons for Bus Errors
X-Git-Tag: v2.6.16-rc3~157
X-Git-Url: http://pilppa.com/gitweb/?a=commitdiff_plain;h=64b4a954b03a1153fb8ae38d6ffbd991e01a1e80;p=linux-2.6-omap-h63xx.git

[PATCH] hugetlb: add comment explaining reasons for Bus Errors

I just spent some time researching a Bus Error.  Turns out that the huge
page fault handler can return VM_FAULT_SIGBUS for various conditions where
no huge page is available.

Add a note explaining the reasoning in the source.

Signed-off-by: Christoph Lameter <clameter@sgi.com>
Acked-by: William Lee Irwin III <wli@holomorphy.com>
Cc: Hugh Dickins <hugh@veritas.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
---

diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index b21d78c941b..ceb3ebb3c39 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -444,6 +444,15 @@ retry:
 		page = alloc_huge_page(vma, address);
 		if (!page) {
 			hugetlb_put_quota(mapping);
+			/*
+		 	 * No huge pages available. So this is an OOM
+			 * condition but we do not want to trigger the OOM
+			 * killer, so we return VM_FAULT_SIGBUS.
+			 *
+			 * A program using hugepages may fault with Bus Error
+			 * because no huge pages are available in the cpuset, per
+			 * memory policy or because all are in use!
+			 */
 			goto out;
 		}