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 kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by smtp.lore.kernel.org (Postfix) with ESMTP id 887D5C433EF for ; Mon, 20 Dec 2021 15:02:47 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 9540B6B0071; Mon, 20 Dec 2021 10:02:46 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id 902D96B0073; Mon, 20 Dec 2021 10:02:46 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 7F1E86B0074; Mon, 20 Dec 2021 10:02:46 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0180.hostedemail.com [216.40.44.180]) by kanga.kvack.org (Postfix) with ESMTP id 70E946B0071 for ; Mon, 20 Dec 2021 10:02:46 -0500 (EST) Received: from smtpin19.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay01.hostedemail.com (Postfix) with ESMTP id 243AE180D32F9 for ; Mon, 20 Dec 2021 15:02:46 +0000 (UTC) X-FDA: 78938489532.19.27A8722 Received: from mail-ua1-f44.google.com (mail-ua1-f44.google.com [209.85.222.44]) by imf09.hostedemail.com (Postfix) with ESMTP id EF467140043 for ; Mon, 20 Dec 2021 15:02:40 +0000 (UTC) Received: by mail-ua1-f44.google.com with SMTP id i6so18189151uae.6 for ; 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=E1cJR3tvBEzEIuB/ZL4UECSiGcridcpl8Yf1doKRWLMkSvqVCfPujbEzh40jxj4itq 0l4IFZRflpiG29bM+1AJCxUP5CGp0JfpYMp0CF5q40NS2g0T/VQ8aFgMzFnPUDNjx2tm zlSzBVPZl2EINoDSuaaREwtEk4dJp8+7RnnOpb4F+XcoH61TlYqEn7SoLjFYaCP8Xgwn 5h6X+Fi5bOy8QrkGBkF1ZI2pHseaLb9MGvVMIF21w7874y/bWXOSCmYGzg8SZ3SrhAb8 /wLuD82meanaYZUyeQqbJaPvQhoxAb9UnJZ0Uqo6Z6cIhs6gNJf0Bpt+keNf+IQuuGRs uuXA== X-Gm-Message-State: AOAM530SE15Nv4wZTGFlNkm1WeDbzaDdDisWR4yZ7EZkjwLP/QrOfd1X ooZjCQYmZsL2FssTuW9pZv591/8AU1wsBltbDOI= 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" Authentication-Results: imf09.hostedemail.com; dkim=pass header.d=googlemail.com header.s=20210112 header.b=jECDHrGy; dmarc=pass (policy=quarantine) header.from=googlemail.com; spf=pass (imf09.hostedemail.com: domain of markhemm@googlemail.com designates 209.85.222.44 as permitted sender) smtp.mailfrom=markhemm@googlemail.com X-Rspamd-Server: rspam12 X-Rspamd-Queue-Id: EF467140043 X-Stat-Signature: upj7iu56acrcnfqw94a6y3zbi5mxsi6j X-HE-Tag: 1640012560-771955 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: 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