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=-4.1 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS 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 F2C49C433DF for ; Mon, 10 Aug 2020 19:37:32 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id D1BCE22CAE for ; Mon, 10 Aug 2020 19:37:32 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="ivqw4MlX" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728460AbgHJThb (ORCPT ); Mon, 10 Aug 2020 15:37:31 -0400 Received: from us-smtp-delivery-1.mimecast.com ([205.139.110.120]:21363 "EHLO us-smtp-1.mimecast.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1727991AbgHJTha (ORCPT ); Mon, 10 Aug 2020 15:37:30 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1597088249; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=gwOnUO3qnuP34cA5hoah52OJNOZjjOKPyNMz1o/AUDU=; b=ivqw4MlX2kDWERmTNuq17uVJHU/gDfUo6ZCDR1n3RSdmALdmbua6JlQZ6ahlfNN7vVDopB mBrHwN2pLNDue4JD2EwWAdCuBzu5Ou/ftkuP7P/DQp+LCHFWEbaVNeaeiCH3TZYHy2ppUM RM0KLp1lW9l40HTnvAMDBGIlClqrmOI= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-250-7cwZ3q4hMfitOoj3aLxf9A-1; Mon, 10 Aug 2020 15:37:25 -0400 X-MC-Unique: 7cwZ3q4hMfitOoj3aLxf9A-1 Received: from smtp.corp.redhat.com (int-mx05.intmail.prod.int.phx2.redhat.com [10.5.11.15]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 50A9519200C5; Mon, 10 Aug 2020 19:37:24 +0000 (UTC) Received: from horse.redhat.com (unknown [10.10.115.251]) by smtp.corp.redhat.com (Postfix) with ESMTP id 3D0835F1E9; Mon, 10 Aug 2020 19:37:18 +0000 (UTC) Received: by horse.redhat.com (Postfix, from userid 10451) id BCA4422036A; Mon, 10 Aug 2020 15:37:17 -0400 (EDT) Date: Mon, 10 Aug 2020 15:37:17 -0400 From: Vivek Goyal To: Miklos Szeredi Cc: linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, virtio-fs-list , Stefan Hajnoczi , "Dr. David Alan Gilbert" Subject: Re: [PATCH v2 18/20] fuse: Release file in process context Message-ID: <20200810193717.GF455528@redhat.com> References: <20200807195526.426056-1-vgoyal@redhat.com> <20200807195526.426056-19-vgoyal@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Scanned-By: MIMEDefang 2.79 on 10.5.11.15 Sender: linux-fsdevel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org On Mon, Aug 10, 2020 at 10:29:13AM +0200, Miklos Szeredi wrote: > On Fri, Aug 7, 2020 at 9:55 PM Vivek Goyal wrote: > > > > fuse_file_put(sync) can be called with sync=true/false. If sync=true, > > it waits for release request response and then calls iput() in the > > caller's context. If sync=false, it does not wait for release request > > response, frees the fuse_file struct immediately and req->end function > > does the iput(). > > > > iput() can be a problem with DAX if called in req->end context. If this > > is last reference to inode (VFS has let go its reference already), then > > iput() will clean DAX mappings as well and send REMOVEMAPPING requests > > and wait for completion. (All the the worker thread context which is > > processing fuse replies from daemon on the host). > > > > That means it blocks worker thread and it stops processing further > > replies and system deadlocks. > > Is this reasoning specific to DAX? Seems to me this is a virtio-fs > specific issue. Hi Miklos, I am looking at this patch closely and maybe we don't need it, given current code. Reason being that looks like for virtiofs now we set ctx->destroy=true and that sets fc->destroy. And if that's set, we don't schedule async req in fuse_release_common(); fuse_release_common() { fuse_file_put(ff, ff->fc->destroy, isdir); } And if we don't schedule async file put, we don't run the risk of blocking worker thread in evict_inode() with DAX enabled. I ran blogbench multiple times with this patch reverted and I can't reproduce the deadlock. So we can drop this patch for now. If need be I will fix it as post merge patch. Thanks Vivek