From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pd0-f171.google.com (mail-pd0-f171.google.com [209.85.192.171]) by kanga.kvack.org (Postfix) with ESMTP id A815F6B0038 for ; Tue, 17 Mar 2015 04:25:41 -0400 (EDT) Received: by pdbop1 with SMTP id op1so3109542pdb.2 for ; Tue, 17 Mar 2015 01:25:41 -0700 (PDT) Received: from mail-pa0-x22d.google.com (mail-pa0-x22d.google.com. [2607:f8b0:400e:c03::22d]) by mx.google.com with ESMTPS id bh1si27814418pdb.191.2015.03.17.01.25.40 for (version=TLSv1.2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Tue, 17 Mar 2015 01:25:40 -0700 (PDT) Received: by pabyw6 with SMTP id yw6so3143648pab.2 for ; Tue, 17 Mar 2015 01:25:40 -0700 (PDT) From: denc716@gmail.com Subject: [PATCH 1/2] mremap should return -ENOMEM when __vm_enough_memory fail Date: Tue, 17 Mar 2015 01:25:12 -0700 Message-Id: <1426580713-21151-1-git-send-email-denc716@gmail.com> Sender: owner-linux-mm@kvack.org List-ID: To: linux-mm@kvack.org, "Kirill A. Shutemov" , David Rientjes Cc: Derek Che Recently I straced bash behavior in this dd zero pipe to read test, in part of testing under vm.overcommit_memory=2 (OVERCOMMIT_NEVER mode): # dd if=/dev/zero | read x The bash sub shell is calling mremap to reallocate more and more memory untill it finally failed -ENOMEM (I expect), or to be killed by system OOM killer (which should not happen under OVERCOMMIT_NEVER mode); But the mremap system call actually failed of -EFAULT, which is a surprise to me, I think it's supposed to be -ENOMEM? then I wrote this piece of C code testing confirmed it: https://gist.github.com/crquan/326bde37e1ddda8effe5 $ ./remap allocated one page @0x7f686bf71000, (PAGE_SIZE: 4096) grabbed 7680512000 bytes of memory (1875125 pages) @ 00007f6690993000. mremap failed Bad address (14). The -EFAULT comes from the branch of security_vm_enough_memory_mm failure, underlyingly it calls __vm_enough_memory which returns only 0 for success or -ENOMEM; So why vma_to_resize needs to return -EFAULT in this case? this sounds like a mistake to me. Some more digging into git history: 1) Before commit 119f657c7 in May 1 2005 (pre 2.6.12 days) it was returning -ENOMEM for this failure; 2) but commit 119f657c7 changed it accidentally, to what ever is preserved in local ret, which happened to be -EFAULT, in a previous assignment; 3) then in commit 54f5de709 code refactoring, it's explicitly returning -EFAULT, should be wrong. Signed-off-by: Derek Che Acked-by: "Kirill A. Shutemov" Acked-by: David Rientjes --- mm/mremap.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/mm/mremap.c b/mm/mremap.c index 57dadc0..5da81cb 100644 --- a/mm/mremap.c +++ b/mm/mremap.c @@ -375,7 +375,7 @@ static struct vm_area_struct *vma_to_resize(unsigned long addr, if (vma->vm_flags & VM_ACCOUNT) { unsigned long charged = (new_len - old_len) >> PAGE_SHIFT; if (security_vm_enough_memory_mm(mm, charged)) - goto Efault; + goto Enomem; *p = charged; } -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org