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[209.132.183.28]) by mx.google.com with ESMTPS id a22si1066099qkk.142.2019.02.21.07.30.08 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Thu, 21 Feb 2019 07:30:09 -0800 (PST) Received-SPF: pass (google.com: domain of jglisse@redhat.com designates 209.132.183.28 as permitted sender) client-ip=209.132.183.28; Authentication-Results: mx.google.com; spf=pass (google.com: domain of jglisse@redhat.com designates 209.132.183.28 as permitted sender) smtp.mailfrom=jglisse@redhat.com; dmarc=pass (p=NONE sp=NONE dis=NONE) header.from=redhat.com Received: from smtp.corp.redhat.com (int-mx01.intmail.prod.int.phx2.redhat.com [10.5.11.11]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id C204D3DD99; Thu, 21 Feb 2019 15:30:07 +0000 (UTC) Received: from redhat.com (unknown [10.20.6.236]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 63BAE6015C; Thu, 21 Feb 2019 15:29:58 +0000 (UTC) Date: Thu, 21 Feb 2019 10:29:56 -0500 From: Jerome Glisse To: Peter Xu Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, David Hildenbrand , Hugh Dickins , Maya Gokhale , Pavel Emelyanov , Johannes Weiner , Martin Cracauer , Shaohua Li , Marty McFadden , Andrea Arcangeli , Mike Kravetz , Denis Plotnikov , Mike Rapoport , Mel Gorman , "Kirill A . Shutemov" , "Dr . David Alan Gilbert" Subject: Re: [PATCH v2 02/26] mm: userfault: return VM_FAULT_RETRY on signals Message-ID: <20190221152956.GB2813@redhat.com> References: <20190212025632.28946-1-peterx@redhat.com> <20190212025632.28946-3-peterx@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20190212025632.28946-3-peterx@redhat.com> User-Agent: Mutt/1.10.0 (2018-05-17) X-Scanned-By: MIMEDefang 2.79 on 10.5.11.11 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.29]); Thu, 21 Feb 2019 15:30:08 +0000 (UTC) X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Tue, Feb 12, 2019 at 10:56:08AM +0800, Peter Xu wrote: > The idea comes from the upstream discussion between Linus and Andrea: > > https://lkml.org/lkml/2017/10/30/560 > > A summary to the issue: there was a special path in handle_userfault() > in the past that we'll return a VM_FAULT_NOPAGE when we detected > non-fatal signals when waiting for userfault handling. We did that by > reacquiring the mmap_sem before returning. However that brings a risk > in that the vmas might have changed when we retake the mmap_sem and > even we could be holding an invalid vma structure. > > This patch removes the special path and we'll return a VM_FAULT_RETRY > with the common path even if we have got such signals. Then for all > the architectures that is passing in VM_FAULT_ALLOW_RETRY into > handle_mm_fault(), we check not only for SIGKILL but for all the rest > of userspace pending signals right after we returned from > handle_mm_fault(). This can allow the userspace to handle nonfatal > signals faster than before. > > This patch is a preparation work for the next patch to finally remove > the special code path mentioned above in handle_userfault(). > > Suggested-by: Linus Torvalds > Suggested-by: Andrea Arcangeli > Signed-off-by: Peter Xu See maybe minor improvement Reviewed-by: Jérôme Glisse [...] > diff --git a/arch/arm/mm/fault.c b/arch/arm/mm/fault.c > index 58f69fa07df9..c41c021bbe40 100644 > --- a/arch/arm/mm/fault.c > +++ b/arch/arm/mm/fault.c > @@ -314,12 +314,12 @@ do_page_fault(unsigned long addr, unsigned int fsr, struct pt_regs *regs) > > fault = __do_page_fault(mm, addr, fsr, flags, tsk); > > - /* If we need to retry but a fatal signal is pending, handle the > + /* If we need to retry but a signal is pending, handle the > * signal first. We do not need to release the mmap_sem because > * it would already be released in __lock_page_or_retry in > * mm/filemap.c. */ > - if ((fault & VM_FAULT_RETRY) && fatal_signal_pending(current)) { > - if (!user_mode(regs)) > + if (unlikely(fault & VM_FAULT_RETRY && signal_pending(current))) { I rather see (fault & VM_FAULT_RETRY) ie with the parenthesis as it avoids the need to remember operator precedence rules :) [...] > diff --git a/arch/nds32/mm/fault.c b/arch/nds32/mm/fault.c > index 68d5f2a27f38..9f6e477b9e30 100644 > --- a/arch/nds32/mm/fault.c > +++ b/arch/nds32/mm/fault.c > @@ -206,12 +206,12 @@ void do_page_fault(unsigned long entry, unsigned long addr, > fault = handle_mm_fault(vma, addr, flags); > > /* > - * If we need to retry but a fatal signal is pending, handle the > + * If we need to retry but a signal is pending, handle the > * signal first. We do not need to release the mmap_sem because it > * would already be released in __lock_page_or_retry in mm/filemap.c. > */ > - if ((fault & VM_FAULT_RETRY) && fatal_signal_pending(current)) { > - if (!user_mode(regs)) > + if (fault & VM_FAULT_RETRY && signal_pending(current)) { Same as above parenthesis maybe. [...] > diff --git a/arch/um/kernel/trap.c b/arch/um/kernel/trap.c > index 0e8b6158f224..09baf37b65b9 100644 > --- a/arch/um/kernel/trap.c > +++ b/arch/um/kernel/trap.c > @@ -76,8 +76,11 @@ int handle_page_fault(unsigned long address, unsigned long ip, > > fault = handle_mm_fault(vma, address, flags); > > - if ((fault & VM_FAULT_RETRY) && fatal_signal_pending(current)) > + if (fault & VM_FAULT_RETRY && signal_pending(current)) { Same as above parenthesis maybe. [...]