From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-2.5 required=3.0 tests=MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id C133EC3A59E for ; Fri, 16 Aug 2019 12:26:31 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 9249D2064A for ; Fri, 16 Aug 2019 12:26:31 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 9249D2064A Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=kernel.org Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id 2CB466B000A; Fri, 16 Aug 2019 08:26:31 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 256106B000C; Fri, 16 Aug 2019 08:26:31 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 11CA36B000D; Fri, 16 Aug 2019 08:26:31 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0011.hostedemail.com [216.40.44.11]) by kanga.kvack.org (Postfix) with ESMTP id DDD076B000A for ; Fri, 16 Aug 2019 08:26:30 -0400 (EDT) Received: from smtpin21.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay05.hostedemail.com (Postfix) with SMTP id 8A27A181AC9D3 for ; Fri, 16 Aug 2019 12:26:30 +0000 (UTC) X-FDA: 75828214140.21.game83_38c2c30f65710 X-HE-Tag: game83_38c2c30f65710 X-Filterd-Recvd-Size: 4115 Received: from mx1.suse.de (mx2.suse.de [195.135.220.15]) by imf22.hostedemail.com (Postfix) with ESMTP for ; Fri, 16 Aug 2019 12:26:29 +0000 (UTC) X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.220.254]) by mx1.suse.de (Postfix) with ESMTP id 0F587AF55; Fri, 16 Aug 2019 12:26:28 +0000 (UTC) Date: Fri, 16 Aug 2019 14:26:25 +0200 From: Michal Hocko To: Jason Gunthorpe Cc: LKML , linux-mm@kvack.org, DRI Development , Intel Graphics Development , Peter Zijlstra , Ingo Molnar , Andrew Morton , David Rientjes , Christian =?iso-8859-1?Q?K=F6nig?= , =?iso-8859-1?B?Suly9G1l?= Glisse , Masahiro Yamada , Wei Wang , Andy Shevchenko , Thomas Gleixner , Jann Horn , Feng Tang , Kees Cook , Randy Dunlap , Daniel Vetter Subject: Re: [PATCH 2/5] kernel.h: Add non_block_start/end() Message-ID: <20190816122625.GA10499@dhcp22.suse.cz> References: <20190815155950.GN9477@dhcp22.suse.cz> <20190815165631.GK21596@ziepe.ca> <20190815174207.GR9477@dhcp22.suse.cz> <20190815182448.GP21596@ziepe.ca> <20190815190525.GS9477@dhcp22.suse.cz> <20190815191810.GR21596@ziepe.ca> <20190815193526.GT9477@dhcp22.suse.cz> <20190815201323.GU21596@ziepe.ca> <20190816081029.GA27790@dhcp22.suse.cz> <20190816121906.GC5398@ziepe.ca> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190816121906.GC5398@ziepe.ca> User-Agent: Mutt/1.10.1 (2018-07-13) 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: Archived-At: List-Archive: List-Post: On Fri 16-08-19 09:19:06, Jason Gunthorpe wrote: > On Fri, Aug 16, 2019 at 10:10:29AM +0200, Michal Hocko wrote: > > On Thu 15-08-19 17:13:23, Jason Gunthorpe wrote: > > > On Thu, Aug 15, 2019 at 09:35:26PM +0200, Michal Hocko wrote: > > > > > > > > The last detail is I'm still unclear what a GFP flags a blockable > > > > > invalidate_range_start() should use. Is GFP_KERNEL OK? > > > > > > > > I hope I will not make this muddy again ;) > > > > invalidate_range_start in the blockable mode can use/depend on any sleepable > > > > allocation allowed in the context it is called from. > > > > > > 'in the context is is called from' is the magic phrase, as > > > invalidate_range_start is called while holding several different mm > > > related locks. I know at least write mmap_sem and i_mmap_rwsem > > > (write?) > > > > > > Can GFP_KERNEL be called while holding those locks? > > > > i_mmap_rwsem would be problematic because it is taken during the > > reclaim. > > Okay.. So the fs_reclaim debugging does catch errors. I do not think fs_reclaim is the udnerlying mechanism to catch this deadlock. It is a simple AA deadlock. You take i_mmap_rwsem and then go down the allocation path, direct reclaim and take the lock again. Nothing really surprising. fs_reclaim is really to catch GFP_NOFS context calling into a less restricted (e.g. GFP_KERNEL allocation context). > Do you have any > reference for what a false positive looks like? I believe I have given some examples when introducing __GFP_NOLOCKDEP. > I would like to inject it into the notifier path as this is very > difficult for driver authors to discover and know about, but I'm > worried about your false positive remark. > > I think I understand we can use only GFP_ATOMIC in the notifiers, but > we need a strategy to handle OOM to guarentee forward progress. Your example is from the notifier registration IIUC. Can you pre-allocate before taking locks? Could you point me to some examples when the allocation is necessary in the range notifier callback? -- Michal Hocko SUSE Labs