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 797A9C433EF for ; Mon, 20 Dec 2021 15:23:17 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S239836AbhLTPXN (ORCPT ); Mon, 20 Dec 2021 10:23:13 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:41420 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S237802AbhLTPWc (ORCPT ); Mon, 20 Dec 2021 10:22:32 -0500 Received: from mail-ua1-x92d.google.com (mail-ua1-x92d.google.com [IPv6:2607:f8b0:4864:20::92d]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 93FB8C08EA6B; Mon, 20 Dec 2021 07:02:45 -0800 (PST) Received: by mail-ua1-x92d.google.com with SMTP id y22so18222388uap.2; Mon, 20 Dec 2021 07:02:45 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=googlemail.com; s=20210112; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=y5dsjn45w/r98lY9eOdxUUnyPxII4scBtnfEACcCO3I=; b=jECDHrGyp8EcXQWOuodyJm8wNMsr+QhOLFHPqoSrLvKczC+V0Btd4Kmn92Mfcvpg7i y9cDgEoxxxbiLVgwKDz0tEXyng9UNi98eFKAduJz4zwLi/QLi9DbjRnIWOX0xIc5Emwo 8CnWUBv6/u/HdFwTanL0lPRWBOqY9TR75+Sq/qZlG9uEWTS8qmiNxyfVu3/X56AcWd9n +wlShoeZf2E1hqCN49fq0Ocabn/UvnMmVKOmDPs8HI/2qHLzP/tcvGO0T50CGqV82dRR 5a1pmNSWlrW5aAGMzXn08KVJ2rIlryjagDozCv0YYeNKiTN30o9YevNEhn60QJ+3gNQt +MBA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=y5dsjn45w/r98lY9eOdxUUnyPxII4scBtnfEACcCO3I=; b=ZQbzztM0TyCX3Z1OIPM0v4qn9RZCQKsRK52OrR2bgwLHGzfnGFWT8aLEtbgPhzhuKE RzfRQZVXPy1Hm9lMS7XP+1INNhr7eWaKspBcfXxyIlDriJ/FevHQ4VwXutxVOPM4NzkP ZO9YM/EYr5lh7TCumDF5dT4cs5JEJqfy0NE5qD03oG0GltgToMRUzwbipmBGF01mLjjp sSHiW7abS5GvEVIiHpS1WKBbw9zreK1PB4tIKsqDya1gmQrkDDz9HIBSxkMVlPFWd6Y4 C4RYAwJ7bBpD4RE73bIZ9+7FDNiyHj0ya54Pt9QxpGjlvz+4oAcx2X42c8W7M6YXbEnC 0qqA== X-Gm-Message-State: AOAM530fwVDe+DwGbsEyzJxN/wLXp6WCwiTNwQhYB6vbF8ZP6HWQEHv5 w0P1h5u0HHYkP7F6EbgfU+wgmoZCeCbpQ7G0yd35COSjMVE= X-Google-Smtp-Source: ABdhPJw4yGR5YShQXGrvI3EY9qxOpbI14WmP9yRcJCevDole2egJsXglkfKn1fdLgU3CAZ+nSQoriiflUSjIa/a7EAU= X-Received: by 2002:a9f:35ad:: with SMTP id t42mr5302353uad.105.1640012562772; Mon, 20 Dec 2021 07:02:42 -0800 (PST) MIME-Version: 1.0 References: <163969801519.20885.3977673503103544412.stgit@noble.brown> <163969850314.20885.13214679186436457787.stgit@noble.brown> In-Reply-To: <163969850314.20885.13214679186436457787.stgit@noble.brown> From: Mark Hemment Date: Mon, 20 Dec 2021 15:02:31 +0000 Message-ID: Subject: Re: [PATCH 10/18] NFS: swap IO handling is slightly different for O_DIRECT IO To: NeilBrown Cc: Trond Myklebust , Anna Schumaker , Chuck Lever , Andrew Morton , Mel Gorman , Christoph Hellwig , David Howells , linux-nfs@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org Content-Type: text/plain; charset="UTF-8" Precedence: bulk List-ID: X-Mailing-List: linux-nfs@vger.kernel.org On Thu, 16 Dec 2021 at 23:58, NeilBrown wrote: > > 1/ Taking the i_rwsem for swap IO triggers lockdep warnings regarding > possible deadlocks with "fs_reclaim". These deadlocks could, I believe, > eventuate if a buffered read on the swapfile was attempted. > > We don't need coherence with the page cache for a swap file, and > buffered writes are forbidden anyway. There is no other need for > i_rwsem during direct IO. So never take it for swap_rw() Agreed. I cannot see an issue with not taking the sem. > 2/ generic_write_checks() explicitly forbids writes to swap, and > performs checks that are not needed for swap. So bypass it > for swap_rw(). > > Signed-off-by: NeilBrown > --- ... > diff --git a/fs/nfs/file.c b/fs/nfs/file.c > @@ -625,7 +625,7 @@ ssize_t nfs_file_write(struct kiocb *iocb, struct iov_iter *from) > return result; > > if (iocb->ki_flags & IOCB_DIRECT) > - return nfs_file_direct_write(iocb, from); > + return nfs_file_direct_write(iocb, from, false); > > dprintk("NFS: write(%pD2, %zu@%Ld)\n", > file, iov_iter_count(from), (long long) iocb->ki_pos); This code at the top of nfs/file.c should be removed; /* Hack for future NFS swap support */ #ifndef IS_SWAPFILE # define IS_SWAPFILE(inode) (0) #endif As IS_SWAPFILE() is used just below this diff (to prevent buffered writes), better be using a non-hacked version. Mark