From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-we0-f175.google.com (mail-we0-f175.google.com [74.125.82.175]) by kanga.kvack.org (Postfix) with ESMTP id 6F9D36B00AC for ; Fri, 13 Mar 2015 06:39:53 -0400 (EDT) Received: by wesx3 with SMTP id x3so22367850wes.1 for ; Fri, 13 Mar 2015 03:39:52 -0700 (PDT) Received: from kirsi1.inet.fi (mta-out1.inet.fi. [62.71.2.195]) by mx.google.com with ESMTP id r19si2438671wik.45.2015.03.13.03.39.51 for ; Fri, 13 Mar 2015 03:39:51 -0700 (PDT) Date: Fri, 13 Mar 2015 12:39:49 +0200 From: "Kirill A. Shutemov" Subject: Re: [PATCH] mremap should return -ENOMEM when __vm_enough_memory fail Message-ID: <20150313103949.GB7251@node.dhcp.inet.fi> References: <1426238498-21127-1-git-send-email-crquan@ymail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1426238498-21127-1-git-send-email-crquan@ymail.com> Sender: owner-linux-mm@kvack.org List-ID: To: Derek Cc: linux-mm@kvack.org On Fri, Mar 13, 2015 at 02:21:38AM -0700, Derek wrote: > 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 > > 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? > it 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 > --- > 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; > } Looks good to me. But that would be nice to get rid of these pointless gotos. Just plain return would work too. -- Kirill A. Shutemov -- 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