linux-kernel - [PATCH 6/6] mm: sigbus instead of abusing oom

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Date:	Tue, 10 Nov 2009 22:06:49 +0000 (GMT)
From:	Hugh Dickins <hugh.dickins@...cali.co.uk>
To:	Andrew Morton <akpm@...ux-foundation.org>
cc:	Izik Eidus <ieidus@...hat.com>,
	Andrea Arcangeli <aarcange@...hat.com>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Minchan Kim <minchan.kim@...il.com>,
	Andi Kleen <andi@...stfloor.org>,
	Wu Fengguang <fengguang.wu@...el.com>,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: [PATCH 6/6] mm: sigbus instead of abusing oom

When do_nonlinear_fault() realizes that the page table must have been
corrupted for it to have been called, it does print_bad_pte() and
returns ... VM_FAULT_OOM, which is hard to understand.

It made some sense when I did it for 2.6.15, when do_page_fault()
just killed the current process; but nowadays it lets the OOM killer
decide who to kill - so page table corruption in one process would
be liable to kill another.

Change it to return VM_FAULT_SIGBUS instead: that doesn't guarantee
that the process will be killed, but is good enough for such a rare
abnormality, accompanied as it is by the "BUG: Bad page map" message.

And recent HWPOISON work has copied that code into do_swap_page(),
when it finds an impossible swap entry: fix that to VM_FAULT_SIGBUS too.

Signed-off-by: Hugh Dickins <hugh.dickins@...cali.co.uk>
---
This one has nothing whatever to do with KSM swapping,
just something that KAMEZAWA-san and Minchan noticed recently.

 mm/memory.c |    4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

--- mm5/mm/memory.c	2009-11-02 12:32:34.000000000 +0000
+++ mm6/mm/memory.c	2009-11-07 14:44:58.000000000 +0000
@@ -2529,7 +2529,7 @@ static int do_swap_page(struct mm_struct
 			ret = VM_FAULT_HWPOISON;
 		} else {
 			print_bad_pte(vma, address, orig_pte, NULL);
-			ret = VM_FAULT_OOM;
+			ret = VM_FAULT_SIGBUS;
 		}
 		goto out;
 	}
@@ -2925,7 +2925,7 @@ static int do_nonlinear_fault(struct mm_
 		 * Page table corrupted: show pte and kill process.
 		 */
 		print_bad_pte(vma, address, orig_pte, NULL);
-		return VM_FAULT_OOM;
+		return VM_FAULT_SIGBUS;
 	}

 	pgoff = pte_to_pgoff(orig_pte);
--
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