From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pg1-f199.google.com (mail-pg1-f199.google.com [209.85.215.199]) by kanga.kvack.org (Postfix) with ESMTP id EBB596B74DB for ; Wed, 5 Sep 2018 15:58:48 -0400 (EDT) Received: by mail-pg1-f199.google.com with SMTP id d132-v6so4156533pgc.22 for ; Wed, 05 Sep 2018 12:58:48 -0700 (PDT) Received: from mail.linuxfoundation.org (mail.linuxfoundation.org. [140.211.169.12]) by mx.google.com with ESMTPS id p66-v6si2948635pfp.237.2018.09.05.12.58.47 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Wed, 05 Sep 2018 12:58:47 -0700 (PDT) Date: Wed, 5 Sep 2018 12:58:46 -0700 From: Andrew Morton Subject: Re: [RFC PATCH] mm/hugetlb: make hugetlb_lock irq safe Message-Id: <20180905125846.eb0a9ed907b293c1b4c23c23@linux-foundation.org> In-Reply-To: <20180905134848.GB3729@bombadil.infradead.org> References: <20180905112341.21355-1-aneesh.kumar@linux.ibm.com> <20180905130440.GA3729@bombadil.infradead.org> <20180905134848.GB3729@bombadil.infradead.org> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Matthew Wilcox Cc: "Aneesh Kumar K.V" , Mike Kravetz , linux-mm@kvack.org, linux-kernel@vger.kernel.org On Wed, 5 Sep 2018 06:48:48 -0700 Matthew Wilcox wrote: > > I didn't. The reason I looked at current patch is to enable the usage of > > put_page() from irq context. We do allow that for non hugetlb pages. So was > > not sure adding that additional restriction for hugetlb > > is really needed. Further the conversion to irqsave/irqrestore was > > straightforward. > > straightforward, sure. but is it the right thing to do? do we want to > be able to put_page() a hugetlb page from hardirq context? Calling put_page() against a huge page from hardirq seems like the right thing to do - even if it's rare now, it will presumably become more common as the hugepage virus spreads further across the kernel. And the present asymmetry is quite a wart. That being said, arch/powerpc/mm/mmu_context_iommu.c:mm_iommu_free() is the only known site which does this (yes?) so perhaps we could put some stopgap workaround into that site and add a runtime warning into the put_page() code somewhere to detect puttage of huge pages from hardirq and softirq contexts. And attention will need to be paid to -stable backporting. How long has mm_iommu_free() existed, and been doing this?