From patchwork Thu Oct 7 12:50:53 2021 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Brian Foster X-Patchwork-Id: 12541793 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 mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id EA44AC433EF for ; Thu, 7 Oct 2021 12:51:17 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id CCB74610A2 for ; Thu, 7 Oct 2021 12:51:17 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S240581AbhJGMxK (ORCPT ); Thu, 7 Oct 2021 08:53:10 -0400 Received: from us-smtp-delivery-124.mimecast.com ([170.10.133.124]:34562 "EHLO us-smtp-delivery-124.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S240567AbhJGMxJ (ORCPT ); Thu, 7 Oct 2021 08:53:09 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1633611076; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:mime-version:mime-version: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=TFYsXsjKHiwkpIeXVEQHtA3i5zfhA/KHpy7zFshdwUk=; b=fPB7aC43etkjYIhARwaApUX2HHnQK4h1W4ZSzEBM2qvViLUHMh7RlwcTOyE2SlgTn/ykeD ZauSenMV1+/uR8so0bpGGpzzZtZ+eNMPKBXfxPe+bAH9qh2o4s/vjTjHUA0savS0nHrgU5 3Zsg1iTv4PFPxcrZFTdk/HZTh95GfCU= 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-312-sG63N8YNPFiIUp5zv2uSNg-1; Thu, 07 Oct 2021 08:50:58 -0400 X-MC-Unique: sG63N8YNPFiIUp5zv2uSNg-1 Received: from smtp.corp.redhat.com (int-mx01.intmail.prod.int.phx2.redhat.com [10.5.11.11]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 9E10A1B2C996 for ; Thu, 7 Oct 2021 12:50:57 +0000 (UTC) Received: from bfoster.redhat.com (unknown [10.22.18.206]) by smtp.corp.redhat.com (Postfix) with ESMTP id 412C7652B4 for ; Thu, 7 Oct 2021 12:50:57 +0000 (UTC) From: Brian Foster To: linux-xfs@vger.kernel.org Subject: [PATCH 3/3] xfs: terminate perag iteration reliably on end agno Date: Thu, 7 Oct 2021 08:50:53 -0400 Message-Id: <20211007125053.1096868-4-bfoster@redhat.com> In-Reply-To: <20211007125053.1096868-1-bfoster@redhat.com> References: <20211007125053.1096868-1-bfoster@redhat.com> MIME-Version: 1.0 X-Scanned-By: MIMEDefang 2.79 on 10.5.11.11 Precedence: bulk List-ID: X-Mailing-List: linux-xfs@vger.kernel.org The for_each_perag*() set of macros are hacky in that some (i.e. those based on sb_agcount) rely on the assumption that perag iteration terminates naturally with a NULL perag at the specified end agno. Others allow for the final AG to have a valid perag and require the calling function to clean up any potential leftover xfs_perag reference on termination of the loop. Aside from providing a subtly inconsistent interface, the former variant is racy with a potential growfs in progress because growfs can create discoverable post-eofs perags before the final superblock update that completes the grow operation and increases sb_agcount. This leads to unexpected assert failures (reproduced by xfs/104) such as the following in the superblock buffer write verifier path: XFS: Assertion failed: agno < mp->m_sb.sb_agcount, file: fs/xfs/libxfs/xfs_types.c, line: 22 This occurs because the perag loop in xfs_icount_range() finds and attempts to process a perag struct where pag_agno == sb_agcount. The following assert failure occasionally triggers during the xfs_perag free path on unmount, presumably because one of the many for_each_perag() loops in the code that is expected to terminate with a NULL pag raced with a growfs and actually terminated with a non-NULL reference to post-eofs (at the time) perag. XFS: Assertion failed: atomic_read(&pag->pag_ref) == 0, file: fs/xfs/libxfs/xfs_ag.c, line: 195 Rework the lower level perag iteration logic to explicitly terminate on the specified end agno, not implicitly rely on pag == NULL as a termination clause and thus avoid these problems. As of this change, the remaining post-loop xfs_perag_put() checks that exist purely to cover the natural termination case (i.e., not mid-loop breaks) are spurious (yet harmless) and can be removed. Signed-off-by: Brian Foster --- fs/xfs/libxfs/xfs_ag.h | 20 ++++++++------------ 1 file changed, 8 insertions(+), 12 deletions(-) diff --git a/fs/xfs/libxfs/xfs_ag.h b/fs/xfs/libxfs/xfs_ag.h index d05c9217c3af..edcdd4fbc225 100644 --- a/fs/xfs/libxfs/xfs_ag.h +++ b/fs/xfs/libxfs/xfs_ag.h @@ -116,34 +116,30 @@ void xfs_perag_put(struct xfs_perag *pag); /* * Perag iteration APIs - * - * XXX: for_each_perag_range() usage really needs an iterator to clean up when - * we terminate at end_agno because we may have taken a reference to the perag - * beyond end_agno. Right now callers have to be careful to catch and clean that - * up themselves. This is not necessary for the callers of for_each_perag() and - * for_each_perag_from() because they terminate at sb_agcount where there are - * no perag structures in tree beyond end_agno. */ static inline struct xfs_perag *xfs_perag_next( struct xfs_perag *pag, - xfs_agnumber_t *agno) + xfs_agnumber_t *agno, + xfs_agnumber_t end_agno) { struct xfs_mount *mp = pag->pag_mount; *agno = pag->pag_agno + 1; xfs_perag_put(pag); - pag = xfs_perag_get(mp, *agno); + pag = NULL; + if (*agno <= end_agno) + pag = xfs_perag_get(mp, *agno); return pag; } #define for_each_perag_range(mp, agno, end_agno, pag) \ for ((pag) = xfs_perag_get((mp), (agno)); \ - (pag) != NULL && (agno) <= (end_agno); \ - (pag) = xfs_perag_next((pag), &(agno))) + (pag) != NULL; \ + (pag) = xfs_perag_next((pag), &(agno), (end_agno))) #define for_each_perag_from(mp, agno, pag) \ - for_each_perag_range((mp), (agno), (mp)->m_sb.sb_agcount, (pag)) + for_each_perag_range((mp), (agno), (mp)->m_sb.sb_agcount - 1, (pag)) #define for_each_perag(mp, agno, pag) \