From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-wr0-f199.google.com (mail-wr0-f199.google.com [209.85.128.199]) by kanga.kvack.org (Postfix) with ESMTP id A516D6B0038 for ; Mon, 3 Apr 2017 08:45:48 -0400 (EDT) Received: by mail-wr0-f199.google.com with SMTP id p64so23944799wrb.18 for ; Mon, 03 Apr 2017 05:45:48 -0700 (PDT) Received: from mx2.suse.de (mx2.suse.de. [195.135.220.15]) by mx.google.com with ESMTPS id z45si19813062wrc.238.2017.04.03.05.45.47 for (version=TLS1 cipher=AES128-SHA bits=128/128); Mon, 03 Apr 2017 05:45:47 -0700 (PDT) Date: Mon, 3 Apr 2017 14:45:44 +0200 From: Michal Hocko Subject: Re: [PATCH] mm/zswap: fix potential deadlock in zswap_frontswap_store() Message-ID: <20170403124544.GN24661@dhcp22.suse.cz> References: <20170331153009.11397-1-aryabinin@virtuozzo.com> <20170403084729.GG24661@dhcp22.suse.cz> 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: Andrey Ryabinin Cc: Shakeel Butt , Seth Jennings , Dan Streetman , Linux MM , LKML , Andrew Morton On Mon 03-04-17 15:37:07, Andrey Ryabinin wrote: > > > On 04/03/2017 11:47 AM, Michal Hocko wrote: > > On Fri 31-03-17 10:00:30, Shakeel Butt wrote: > >> On Fri, Mar 31, 2017 at 8:30 AM, Andrey Ryabinin > >> wrote: > >>> zswap_frontswap_store() is called during memory reclaim from > >>> __frontswap_store() from swap_writepage() from shrink_page_list(). > >>> This may happen in NOFS context, thus zswap shouldn't use __GFP_FS, > >>> otherwise we may renter into fs code and deadlock. > >>> zswap_frontswap_store() also shouldn't use __GFP_IO to avoid recursion > >>> into itself. > >>> > >> > >> Is it possible to enter fs code (or IO) from zswap_frontswap_store() > >> other than recursive memory reclaim? However recursive memory reclaim > >> is protected through PF_MEMALLOC task flag. The change seems fine but > >> IMHO reasoning needs an update. Adding Michal for expert opinion. > > > > Yes this is true. > > Actually, no. I think we have a bug in allocator which may lead to > recursive direct reclaim. > > E.g. for costly order allocations (or order > 0 && > ac->migratetype != MIGRATE_MOVABLE) with __GFP_NOMEMALLOC > (gfp_pfmemalloc_allowed() returns false) __alloc_pages_slowpath() > may call __alloc_pages_direct_compact() and unconditionally clear > PF_MEMALLOC: Not sure what is the bug here. __GFP_NOMEMALLOC is supposed to inhibit PF_MEMALLOC. And we do not recurse to the reclaim path. We only do the compaction. Or what am I missing? -- Michal Hocko SUSE Labs -- 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