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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 970C6C7EE2D for ; Tue, 23 May 2023 16:22:09 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S237525AbjEWQWI (ORCPT ); Tue, 23 May 2023 12:22:08 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:39900 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229453AbjEWQWF (ORCPT ); Tue, 23 May 2023 12:22:05 -0400 Received: from bombadil.infradead.org (bombadil.infradead.org [IPv6:2607:7c80:54:3::133]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 49F4112B; Tue, 23 May 2023 09:22:04 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=bombadil.20210309; h=In-Reply-To:Content-Type:MIME-Version :References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description; bh=d661uJD3QZyNSbDvh1yODoH87KCKXO6AdQINLMKGe10=; b=PJwJqOx+NIMo9E4oIdJHNzHO4x /I3Fbeijrw9ytebTXP/VjCInxuGEyLhyF7xK8tuhjlfrJL+4miepn6rGuZNMr5lVWDLMP5nLFDN5U VmyWpb0tB51Wm0DRUm1Lw8tWZB8qqHaYAUGYCtJnq2/TMNBM6iuUiGBwsjrKPSeuh/a2hcal0qJXW DnEIJi9jkoA0SIeByrBKFfHDsAiHJqK+NGjeIWf0DXni53eZdO6V8ifabwFhdnzm9a/6VWSPaoo3V QLtDo5B4zTthXQWU4qSrbH9mzvYLHucS9j+5ROtP1vDIK6MooC5a/p+4oDUqZF3eqJi6wnkrKyMeo JASpUFUA==; Received: from hch by bombadil.infradead.org with local (Exim 4.96 #2 (Red Hat Linux)) id 1q1Ulo-00Amb7-2r; Tue, 23 May 2023 16:21:56 +0000 Date: Tue, 23 May 2023 09:21:56 -0700 From: Christoph Hellwig To: Jan Kara Cc: Kent Overstreet , cluster-devel@redhat.com, "Darrick J . Wong" , linux-kernel@vger.kernel.org, dhowells@redhat.com, linux-bcachefs@vger.kernel.org, linux-fsdevel@vger.kernel.org, Kent Overstreet Subject: Re: [Cluster-devel] [PATCH 06/32] sched: Add task_struct->faults_disabled_mapping Message-ID: References: <20230509165657.1735798-1-kent.overstreet@linux.dev> <20230509165657.1735798-7-kent.overstreet@linux.dev> <20230510010737.heniyuxazlprrbd6@quack3> <20230523133431.wwrkjtptu6vqqh5e@quack3> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20230523133431.wwrkjtptu6vqqh5e@quack3> X-SRS-Rewrite: SMTP reverse-path rewritten from by bombadil.infradead.org. See http://www.infradead.org/rpr.html Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, May 23, 2023 at 03:34:31PM +0200, Jan Kara wrote: > I've checked the code and AFAICT it is all indeed handled. BTW, I've now > remembered that GFS2 has dealt with the same deadlocks - b01b2d72da25 > ("gfs2: Fix mmap + page fault deadlocks for direct I/O") - in a different > way (by prefaulting pages from the iter before grabbing the problematic > lock and then disabling page faults for the iomap_dio_rw() call). I guess > we should somehow unify these schemes so that we don't have two mechanisms > for avoiding exactly the same deadlock. Adding GFS2 guys to CC. > > Also good that you've written a fstest for this, that is definitely a useful > addition, although I suspect GFS2 guys added a test for this not so long > ago when testing their stuff. Maybe they have a pointer handy? generic/708 is the btrfs version of this. But I think all of the file systems that have this deadlock are actually fundamentally broken because they have a mess up locking hierarchy where page faults take the same lock that is held over the the direct I/ operation. And the right thing is to fix this. I have work in progress for btrfs, and something similar should apply to gfs2, with the added complication that it probably means a revision to their network protocol. I'm absolutely not in favour to add workarounds for thes kind of locking problems to the core kernel. I already feel bad for allowing the small workaround in iomap for btrfs, as just fixing the locking back then would have avoid massive ratholing.