From patchwork Mon Apr 19 18:45:16 2021 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Vivek Goyal X-Patchwork-Id: 12212509 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=-15.8 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_CR_TRAILER,INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS autolearn=ham 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 2CD4AC433ED for ; Mon, 19 Apr 2021 18:45:34 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id E6F9E61360 for ; Mon, 19 Apr 2021 18:45:33 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S239747AbhDSSqC (ORCPT ); Mon, 19 Apr 2021 14:46:02 -0400 Received: from us-smtp-delivery-124.mimecast.com ([170.10.133.124]:50157 "EHLO us-smtp-delivery-124.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S239366AbhDSSqB (ORCPT ); Mon, 19 Apr 2021 14:46:01 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1618857930; 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; bh=1V9/k461e5yNE9L1Zer97sHvtte82Z94GuhY2/j5UQw=; b=Ix8CLrAo5a4JPxZoYmWiLsBKRD564tBXIwDPhivGkbPId6Jc7CPa+n0XRaB5nJd1MZ7MS5 oaC8PdAPajof3tgLuYM5KJC529uW0HwJEl4AaIPNHKDKqKroxe6+gsXdbBv6Hn0y0VdRCS QmyUQqwp+9s414ckAQ3c0mWwOIvXFJg= 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-494-TSfOH08yP9OyXg1DKMwK9A-1; Mon, 19 Apr 2021 14:45:27 -0400 X-MC-Unique: TSfOH08yP9OyXg1DKMwK9A-1 Received: from smtp.corp.redhat.com (int-mx03.intmail.prod.int.phx2.redhat.com [10.5.11.13]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 006688030A0; Mon, 19 Apr 2021 18:45:26 +0000 (UTC) Received: from horse.redhat.com (ovpn-116-35.rdu2.redhat.com [10.10.116.35]) by smtp.corp.redhat.com (Postfix) with ESMTP id 33BA460C5C; Mon, 19 Apr 2021 18:45:17 +0000 (UTC) Received: by horse.redhat.com (Postfix, from userid 10451) id BBB6922054F; Mon, 19 Apr 2021 14:45:16 -0400 (EDT) Date: Mon, 19 Apr 2021 14:45:16 -0400 From: Vivek Goyal To: Linux fsdevel mailing list , Jan Kara , Dan Williams , willy@infradead.org Cc: virtio-fs-list , Sergio Lopez , Miklos Szeredi , linux-nvdimm@lists.01.org, linux kernel mailing list Subject: [PATCH][v2] dax: Fix missed wakeup during dax entry invalidation Message-ID: <20210419184516.GC1472665@redhat.com> MIME-Version: 1.0 Content-Disposition: inline X-Scanned-By: MIMEDefang 2.79 on 10.5.11.13 Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org This is V2 of the patch. Posted V1 here. https://lore.kernel.org/linux-fsdevel/20210416173524.GA1379987@redhat.com/ Based on feedback from Dan and Jan, modified the patch to wake up all waiters when dax entry is invalidated. This solves the issues of missed wakeups. I am seeing missed wakeups which ultimately lead to a deadlock when I am using virtiofs with DAX enabled and running "make -j". I had to mount virtiofs as rootfs and also reduce to dax window size to 256M to reproduce the problem consistently. So here is the problem. put_unlocked_entry() wakes up waiters only if entry is not null as well as !dax_is_conflict(entry). But if I call multiple instances of invalidate_inode_pages2() in parallel, then I can run into a situation where there are waiters on this index but nobody will wait these. invalidate_inode_pages2() invalidate_inode_pages2_range() invalidate_exceptional_entry2() dax_invalidate_mapping_entry_sync() __dax_invalidate_entry() { xas_lock_irq(&xas); entry = get_unlocked_entry(&xas, 0); ... ... dax_disassociate_entry(entry, mapping, trunc); xas_store(&xas, NULL); ... ... put_unlocked_entry(&xas, entry); xas_unlock_irq(&xas); } Say a fault in in progress and it has locked entry at offset say "0x1c". Now say three instances of invalidate_inode_pages2() are in progress (A, B, C) and they all try to invalidate entry at offset "0x1c". Given dax entry is locked, all tree instances A, B, C will wait in wait queue. When dax fault finishes, say A is woken up. It will store NULL entry at index "0x1c" and wake up B. When B comes along it will find "entry=0" at page offset 0x1c and it will call put_unlocked_entry(&xas, 0). And this means put_unlocked_entry() will not wake up next waiter, given the current code. And that means C continues to wait and is not woken up. This patch fixes the issue by waking up all waiters when a dax entry has been invalidated. This seems to fix the deadlock I am facing and I can make forward progress. Reported-by: Sergio Lopez Signed-off-by: Vivek Goyal --- fs/dax.c | 12 ++++++------ 1 file changed, 6 insertions(+), 6 deletions(-) Index: redhat-linux/fs/dax.c =================================================================== --- redhat-linux.orig/fs/dax.c 2021-04-16 14:16:44.332140543 -0400 +++ redhat-linux/fs/dax.c 2021-04-19 11:24:11.465213474 -0400 @@ -264,11 +264,11 @@ static void wait_entry_unlocked(struct x finish_wait(wq, &ewait.wait); } -static void put_unlocked_entry(struct xa_state *xas, void *entry) +static void put_unlocked_entry(struct xa_state *xas, void *entry, bool wake_all) { /* If we were the only waiter woken, wake the next one */ if (entry && !dax_is_conflict(entry)) - dax_wake_entry(xas, entry, false); + dax_wake_entry(xas, entry, wake_all); } /* @@ -622,7 +622,7 @@ struct page *dax_layout_busy_page_range( entry = get_unlocked_entry(&xas, 0); if (entry) page = dax_busy_page(entry); - put_unlocked_entry(&xas, entry); + put_unlocked_entry(&xas, entry, false); if (page) break; if (++scanned % XA_CHECK_SCHED) @@ -664,7 +664,7 @@ static int __dax_invalidate_entry(struct mapping->nrexceptional--; ret = 1; out: - put_unlocked_entry(&xas, entry); + put_unlocked_entry(&xas, entry, true); xas_unlock_irq(&xas); return ret; } @@ -943,7 +943,7 @@ static int dax_writeback_one(struct xa_s return ret; put_unlocked: - put_unlocked_entry(xas, entry); + put_unlocked_entry(xas, entry, false); return ret; } @@ -1684,7 +1684,7 @@ dax_insert_pfn_mkwrite(struct vm_fault * /* Did we race with someone splitting entry or so? */ if (!entry || dax_is_conflict(entry) || (order == 0 && !dax_is_pte_entry(entry))) { - put_unlocked_entry(&xas, entry); + put_unlocked_entry(&xas, entry, false); xas_unlock_irq(&xas); trace_dax_insert_pfn_mkwrite_no_entry(mapping->host, vmf, VM_FAULT_NOPAGE);