From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pg1-f200.google.com (mail-pg1-f200.google.com [209.85.215.200]) by kanga.kvack.org (Postfix) with ESMTP id 440446B736A for ; Wed, 5 Sep 2018 09:48:52 -0400 (EDT) Received: by mail-pg1-f200.google.com with SMTP id f32-v6so3695416pgm.14 for ; Wed, 05 Sep 2018 06:48:52 -0700 (PDT) Received: from bombadil.infradead.org (bombadil.infradead.org. [2607:7c80:54:e::133]) by mx.google.com with ESMTPS id t8-v6si1910572plz.126.2018.09.05.06.48.51 for (version=TLS1_2 cipher=ECDHE-RSA-CHACHA20-POLY1305 bits=256/256); Wed, 05 Sep 2018 06:48:51 -0700 (PDT) Date: Wed, 5 Sep 2018 06:48:48 -0700 From: Matthew Wilcox Subject: Re: [RFC PATCH] mm/hugetlb: make hugetlb_lock irq safe Message-ID: <20180905134848.GB3729@bombadil.infradead.org> References: <20180905112341.21355-1-aneesh.kumar@linux.ibm.com> <20180905130440.GA3729@bombadil.infradead.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Sender: owner-linux-mm@kvack.org List-ID: To: "Aneesh Kumar K.V" Cc: akpm@linux-foundation.org, Mike Kravetz , linux-mm@kvack.org, linux-kernel@vger.kernel.org On Wed, Sep 05, 2018 at 06:56:19PM +0530, Aneesh Kumar K.V wrote: > On 09/05/2018 06:34 PM, Matthew Wilcox wrote: > > On Wed, Sep 05, 2018 at 04:53:41PM +0530, Aneesh Kumar K.V wrote: > > > inconsistent {SOFTIRQ-ON-W} -> {IN-SOFTIRQ-W} usage. > > > > How do you go from "can be taken in softirq context" problem report to > > "must disable hard interrupts" solution? Please explain why spin_lock_bh() > > is not a sufficient fix. > > > > > swapper/68/0 [HC0[0]:SC1[1]:HE1:SE0] takes: > > > 0000000052a030a7 (hugetlb_lock){+.?.}, at: free_huge_page+0x9c/0x340 > > > {SOFTIRQ-ON-W} state was registered at: > > > lock_acquire+0xd4/0x230 > > > _raw_spin_lock+0x44/0x70 > > > set_max_huge_pages+0x4c/0x360 > > > hugetlb_sysctl_handler_common+0x108/0x160 > > > proc_sys_call_handler+0x134/0x190 > > > __vfs_write+0x3c/0x1f0 > > > vfs_write+0xd8/0x220 > > > > Also, this only seems to trigger here. Is it possible we _already_ > > have softirqs disabled through every other code path, and it's just this > > one sysctl handler that needs to disable softirqs? Rather than every > > lock access? > > Are you asking whether I looked at moving that put_page to a worker thread? No. I'm asking "why not disable softirqs in the sysctl handler". Or perhaps equivalently, just replace spin_lock() with spin_lock_bh() in set_max_huge_pages(). > 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?