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 39AF8C433EF for ; Thu, 16 Dec 2021 23:53:33 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230043AbhLPXxc (ORCPT ); Thu, 16 Dec 2021 18:53:32 -0500 Received: from smtp-out2.suse.de ([195.135.220.29]:56390 "EHLO smtp-out2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230021AbhLPXxb (ORCPT ); Thu, 16 Dec 2021 18:53:31 -0500 Received: from imap2.suse-dmz.suse.de (imap2.suse-dmz.suse.de [192.168.254.74]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (P-521) server-digest SHA512) (No client certificate requested) by smtp-out2.suse.de (Postfix) with ESMTPS id 3BF111F37F; Thu, 16 Dec 2021 23:53:30 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.de; s=susede2_rsa; t=1639698810; h=from:from:reply-to:date:date:message-id:message-id:to:to:cc:cc: mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=oGTqKoZtDbecvGBIGtaMZLZto4uBvaDYc0Rr0u4Yk7Y=; b=F/0SodB8h/JFf0rkMNTpd82YsL5klsKADLO6pIw1l5DpFt1p9ujNX8ueg7w5b/qmq2Nnc6 qwRxiMTEpgnXS5XO5NK2eFxn1rpKkD5PmErLwPz1iKgWFynGXvJGVg2UlaoBv8jd0IPXde aILXgvTfZrYoGYh0JI2QfHyPfEIQgu4= DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=suse.de; s=susede2_ed25519; t=1639698810; h=from:from:reply-to:date:date:message-id:message-id:to:to:cc:cc: mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=oGTqKoZtDbecvGBIGtaMZLZto4uBvaDYc0Rr0u4Yk7Y=; b=xzsyfzA9n55B/z+zyLwZLTkmRlrd0ulkqRD2eAjVT4r01nfuDLGfVF5Lp/QtywROKLXJez cCoFecD39KUGYRCA== Received: from imap2.suse-dmz.suse.de (imap2.suse-dmz.suse.de [192.168.254.74]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (P-521) server-digest SHA512) (No client certificate requested) by imap2.suse-dmz.suse.de (Postfix) with ESMTPS id 30DC313EFD; Thu, 16 Dec 2021 23:53:26 +0000 (UTC) Received: from dovecot-director2.suse.de ([192.168.254.65]) by imap2.suse-dmz.suse.de with ESMTPSA id haErN3bRu2GiWwAAMHmgww (envelope-from ); Thu, 16 Dec 2021 23:53:26 +0000 Subject: [PATCH 10/18] NFS: swap IO handling is slightly different for O_DIRECT IO From: NeilBrown To: Trond Myklebust , Anna Schumaker , Chuck Lever , Andrew Morton , Mel Gorman , Christoph Hellwig , David Howells Cc: linux-nfs@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org Date: Fri, 17 Dec 2021 10:48:23 +1100 Message-ID: <163969850314.20885.13214679186436457787.stgit@noble.brown> In-Reply-To: <163969801519.20885.3977673503103544412.stgit@noble.brown> References: <163969801519.20885.3977673503103544412.stgit@noble.brown> User-Agent: StGit/0.23 MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-nfs@vger.kernel.org 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() 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 --- fs/nfs/direct.c | 30 +++++++++++++++++++++--------- fs/nfs/file.c | 4 ++-- include/linux/nfs_fs.h | 4 ++-- 3 files changed, 25 insertions(+), 13 deletions(-) diff --git a/fs/nfs/direct.c b/fs/nfs/direct.c index f1e169f3050a..eeff1b4e1a7c 100644 --- a/fs/nfs/direct.c +++ b/fs/nfs/direct.c @@ -165,9 +165,9 @@ int nfs_swap_rw(struct kiocb *iocb, struct iov_iter *iter) VM_BUG_ON(iov_iter_count(iter) != PAGE_SIZE); if (iov_iter_rw(iter) == READ) - ret = nfs_file_direct_read(iocb, iter); + ret = nfs_file_direct_read(iocb, iter, true); else - ret = nfs_file_direct_write(iocb, iter); + ret = nfs_file_direct_write(iocb, iter, true); if (ret < 0) return ret; return 0; @@ -421,6 +421,7 @@ static ssize_t nfs_direct_read_schedule_iovec(struct nfs_direct_req *dreq, * nfs_file_direct_read - file direct read operation for NFS files * @iocb: target I/O control block * @iter: vector of user buffers into which to read data + * @swap: flag indicating this is swap IO, not O_DIRECT IO * * We use this function for direct reads instead of calling * generic_file_aio_read() in order to avoid gfar's check to see if @@ -436,7 +437,8 @@ static ssize_t nfs_direct_read_schedule_iovec(struct nfs_direct_req *dreq, * client must read the updated atime from the server back into its * cache. */ -ssize_t nfs_file_direct_read(struct kiocb *iocb, struct iov_iter *iter) +ssize_t nfs_file_direct_read(struct kiocb *iocb, struct iov_iter *iter, + bool swap) { struct file *file = iocb->ki_filp; struct address_space *mapping = file->f_mapping; @@ -478,12 +480,14 @@ ssize_t nfs_file_direct_read(struct kiocb *iocb, struct iov_iter *iter) if (iter_is_iovec(iter)) dreq->flags = NFS_ODIRECT_SHOULD_DIRTY; - nfs_start_io_direct(inode); + if (!swap) + nfs_start_io_direct(inode); NFS_I(inode)->read_io += count; requested = nfs_direct_read_schedule_iovec(dreq, iter, iocb->ki_pos); - nfs_end_io_direct(inode); + if (!swap) + nfs_end_io_direct(inode); if (requested > 0) { result = nfs_direct_wait(dreq); @@ -872,6 +876,7 @@ static ssize_t nfs_direct_write_schedule_iovec(struct nfs_direct_req *dreq, * nfs_file_direct_write - file direct write operation for NFS files * @iocb: target I/O control block * @iter: vector of user buffers from which to write data + * @swap: flag indicating this is swap IO, not O_DIRECT IO * * We use this function for direct writes instead of calling * generic_file_aio_write() in order to avoid taking the inode @@ -888,7 +893,8 @@ static ssize_t nfs_direct_write_schedule_iovec(struct nfs_direct_req *dreq, * Note that O_APPEND is not supported for NFS direct writes, as there * is no atomic O_APPEND write facility in the NFS protocol. */ -ssize_t nfs_file_direct_write(struct kiocb *iocb, struct iov_iter *iter) +ssize_t nfs_file_direct_write(struct kiocb *iocb, struct iov_iter *iter, + bool swap) { ssize_t result, requested; size_t count; @@ -902,7 +908,11 @@ ssize_t nfs_file_direct_write(struct kiocb *iocb, struct iov_iter *iter) dfprintk(FILE, "NFS: direct write(%pD2, %zd@%Ld)\n", file, iov_iter_count(iter), (long long) iocb->ki_pos); - result = generic_write_checks(iocb, iter); + if (!swap) + result = generic_write_checks(iocb, iter); + else + /* bypass generic checks */ + result = iov_iter_count(iter); if (result <= 0) return result; count = result; @@ -933,7 +943,8 @@ ssize_t nfs_file_direct_write(struct kiocb *iocb, struct iov_iter *iter) dreq->iocb = iocb; pnfs_init_ds_commit_info_ops(&dreq->ds_cinfo, inode); - nfs_start_io_direct(inode); + if (!swap) + nfs_start_io_direct(inode); requested = nfs_direct_write_schedule_iovec(dreq, iter, pos); @@ -942,7 +953,8 @@ ssize_t nfs_file_direct_write(struct kiocb *iocb, struct iov_iter *iter) pos >> PAGE_SHIFT, end); } - nfs_end_io_direct(inode); + if (!swap) + nfs_end_io_direct(inode); if (requested > 0) { result = nfs_direct_wait(dreq); diff --git a/fs/nfs/file.c b/fs/nfs/file.c index b620fe697158..996dfb3c74b2 100644 --- a/fs/nfs/file.c +++ b/fs/nfs/file.c @@ -161,7 +161,7 @@ nfs_file_read(struct kiocb *iocb, struct iov_iter *to) ssize_t result; if (iocb->ki_flags & IOCB_DIRECT) - return nfs_file_direct_read(iocb, to); + return nfs_file_direct_read(iocb, to, false); dprintk("NFS: read(%pD2, %zu@%lu)\n", iocb->ki_filp, @@ -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); diff --git a/include/linux/nfs_fs.h b/include/linux/nfs_fs.h index 6329e6958718..3a210478f665 100644 --- a/include/linux/nfs_fs.h +++ b/include/linux/nfs_fs.h @@ -512,9 +512,9 @@ static inline const struct cred *nfs_file_cred(struct file *file) */ extern int nfs_swap_rw(struct kiocb *, struct iov_iter *); extern ssize_t nfs_file_direct_read(struct kiocb *iocb, - struct iov_iter *iter); + struct iov_iter *iter, bool swap); extern ssize_t nfs_file_direct_write(struct kiocb *iocb, - struct iov_iter *iter); + struct iov_iter *iter, bool swap); /* * linux/fs/nfs/dir.c