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 07E46C4167B for ; Tue, 12 Dec 2023 12:42:11 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 7AAA96B02C6; Tue, 12 Dec 2023 07:42:11 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id 7590A6B02C7; Tue, 12 Dec 2023 07:42:11 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 620826B02C8; Tue, 12 Dec 2023 07:42:11 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0012.hostedemail.com [216.40.44.12]) by kanga.kvack.org (Postfix) with ESMTP id 52FE56B02C6 for ; Tue, 12 Dec 2023 07:42:11 -0500 (EST) Received: from smtpin04.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay06.hostedemail.com (Postfix) with ESMTP id 2F948A1E8D for ; Tue, 12 Dec 2023 12:42:11 +0000 (UTC) X-FDA: 81558128862.04.CB1D2E3 Received: from smtp-out1.suse.de (smtp-out1.suse.de [195.135.223.130]) by imf14.hostedemail.com (Postfix) with ESMTP id 81B57100009 for ; Tue, 12 Dec 2023 12:42:08 +0000 (UTC) Authentication-Results: imf14.hostedemail.com; dkim=pass header.d=suse.cz header.s=susede2_rsa header.b=bqifFFBE; dkim=pass header.d=suse.cz header.s=susede2_ed25519 header.b=lJNxfJ9w; dkim=pass header.d=suse.cz header.s=susede2_rsa header.b=0KdH44DZ; dkim=pass header.d=suse.cz header.s=susede2_ed25519 header.b=A2WXGC5F; dmarc=none; spf=pass (imf14.hostedemail.com: domain of jack@suse.cz designates 195.135.223.130 as permitted sender) smtp.mailfrom=jack@suse.cz ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1702384929; h=from:from:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type:content-transfer-encoding: in-reply-to:in-reply-to:references:references:dkim-signature; bh=GNa2E9XZNfaEdk9TRq5PEze1pvUq7Mj5mqzveUCyzc8=; b=srNXY4oSV6NYRCVzVNgkGIj43Y9z1OVt3VKu4iF5kIXIcHnBa6I3o3c5XEK9+M86AiYduy 1660GPZf9QOZ01GgqMCEIVhTRrLkQrmHkQDzdrJvz2kXjEYqJ+fvgsX72YSUgldB2tWw6M 0M1bh63i/S2/t/5PHi1uVcUQUWPWloo= ARC-Authentication-Results: i=1; imf14.hostedemail.com; dkim=pass header.d=suse.cz header.s=susede2_rsa header.b=bqifFFBE; dkim=pass header.d=suse.cz header.s=susede2_ed25519 header.b=lJNxfJ9w; dkim=pass header.d=suse.cz header.s=susede2_rsa header.b=0KdH44DZ; dkim=pass header.d=suse.cz header.s=susede2_ed25519 header.b=A2WXGC5F; dmarc=none; spf=pass (imf14.hostedemail.com: domain of jack@suse.cz designates 195.135.223.130 as permitted sender) smtp.mailfrom=jack@suse.cz ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1702384929; a=rsa-sha256; cv=none; b=bjJISzfWwP7nS7T/jJXD3Z/EUxj9TjicwV0MsO2x2s4YQPIBCcylul0e3Ki1QVNuZDltAd lAP9Nw8bDaohFqVUnbccjSjGfSTtGWKU5YNOYz7wzyPg4PCx69eNHHSUUWjR/N21bhh1R1 zWgJvlZxohGOO8QxCkvETYgnrCkK7Os= Received: from imap2.dmz-prg2.suse.org (imap2.dmz-prg2.suse.org [IPv6:2a07:de40:b281:104:10:150:64:98]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (4096 bits) server-digest SHA256) (No client certificate requested) by smtp-out1.suse.de (Postfix) with ESMTPS id 727C4224EA; Tue, 12 Dec 2023 12:42:04 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.cz; s=susede2_rsa; t=1702384926; h=from:from:reply-to:date:date:message-id:message-id:to:to:cc:cc: mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=GNa2E9XZNfaEdk9TRq5PEze1pvUq7Mj5mqzveUCyzc8=; b=bqifFFBE0MhFbajnZEhW24Eq1ViJGdjcEWsq8/k47JzaQI32MX0l2kkMiLOAcNPPtKJ5RD zOIv/B4mVuNNMoGK0+kV6vI5YQY7PviQqA8T490SCZVa2phLk3VERKJMsA12a1aGaOCILW m/aammhjVPXoytUIrSiVDtcqg6NgXqE= DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=suse.cz; s=susede2_ed25519; t=1702384926; h=from:from:reply-to:date:date:message-id:message-id:to:to:cc:cc: mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=GNa2E9XZNfaEdk9TRq5PEze1pvUq7Mj5mqzveUCyzc8=; b=lJNxfJ9whX7J5ojbi7z5RYhIfbUF5l/rie01DhjSXemSuWafRNwkvQCIu4erc8VQGYxC1X pBgiA/J7AaxpkIDw== DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.cz; s=susede2_rsa; t=1702384924; h=from:from:reply-to:date:date:message-id:message-id:to:to:cc:cc: mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=GNa2E9XZNfaEdk9TRq5PEze1pvUq7Mj5mqzveUCyzc8=; b=0KdH44DZYQRGMDTrAM0LQjrUQAS8V3NaAYeDzWeKE87PTrDaebUZcqWItMEjrvBcOgiTmp 7RxHdmBMXOWgtyGJrqmZLqncXjLQUl4s9wKm4mxDw5lV6rNNfSyNwLoEQEcxjWZDpv4YKH E8q8gi3f/Zfp7AcVNkEjNZpc7gP1evA= DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=suse.cz; s=susede2_ed25519; t=1702384924; h=from:from:reply-to:date:date:message-id:message-id:to:to:cc:cc: mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=GNa2E9XZNfaEdk9TRq5PEze1pvUq7Mj5mqzveUCyzc8=; b=A2WXGC5FP449rylXKqpbXvaibLTsm5cCAdgmCw5kuqGzNYV2jWUDlTNJduF61STFzuMqqc AhDFoFLB7KVT6oCA== Received: from imap2.dmz-prg2.suse.org (localhost [127.0.0.1]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (4096 bits) server-digest SHA256) (No client certificate requested) by imap2.dmz-prg2.suse.org (Postfix) with ESMTPS id 5CFDF132DC; Tue, 12 Dec 2023 12:42:04 +0000 (UTC) Received: from dovecot-director2.suse.de ([10.150.64.162]) by imap2.dmz-prg2.suse.org with ESMTPSA id pImyFhxVeGWJMgAAn2gu4w (envelope-from ); Tue, 12 Dec 2023 12:42:04 +0000 Received: by quack3.suse.cz (Postfix, from userid 1000) id C6A01A06E5; Tue, 12 Dec 2023 13:41:57 +0100 (CET) Date: Tue, 12 Dec 2023 13:41:57 +0100 From: Jan Kara To: Baokun Li Cc: linux-mm@kvack.org, linux-ext4@vger.kernel.org, tytso@mit.edu, adilger.kernel@dilger.ca, jack@suse.cz, willy@infradead.org, akpm@linux-foundation.org, david@fromorbit.com, hch@infradead.org, ritesh.list@gmail.com, linux-kernel@vger.kernel.org, yi.zhang@huawei.com, yangerkun@huawei.com, yukuai3@huawei.com, stable@kernel.org Subject: Re: [RFC PATCH] mm/filemap: avoid buffered read/write race to read inconsistent data Message-ID: <20231212124157.ew6q6jp2wsezvqzd@quack3> References: <20231212093634.2464108-1-libaokun1@huawei.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20231212093634.2464108-1-libaokun1@huawei.com> X-Rspam-User: X-Rspamd-Server: rspam12 X-Rspamd-Queue-Id: 81B57100009 X-Stat-Signature: hszchzp67kdhk3mi6n565ezpf8r7kjsi X-HE-Tag: 1702384928-229024 X-HE-Meta: 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 M0SJ4jJ2 pl3qo0JxIM/1faNtroA4S8bnQhpq+64xUX5nHBVLuTeOdJCk5zQ4MOu2U0BFIQzKdj480pQHmAgSKm4ixS7eycgslo24/w8SrlEYyHg12Lw8ec7cT6BChtkh+pAEdwlTHc5wg7QnCl6nWXZXQ2JQp97RoqvXyL11nRV2vfGJ8YDF2prNw2C+4BLGNZUswCOwDvOCOk3vD8H0XXtzb25koAgl1w91kG012uJVfg7KBtYgyy9Q7RYVd2xto1kv46D0oarjaUHDvSuMYF8x7A251OpoChOlPqk0tjIxSzc3MqLmuo3RLVG0WEqBI0iAHMi5EtEt1MajvvVnFkJ1+cLebW18mmlR8qza9kO8Nc0FPi0hehbE8Anv0HmEn8nAWFLsO6HYmj7Nbgp3FRG0lDFCKYOsR2dnhpXZTdoKaN37d08Qrv6MXEHzGvk1Rzg== 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: List-Subscribe: List-Unsubscribe: On Tue 12-12-23 17:36:34, Baokun Li wrote: > The following concurrency may cause the data read to be inconsistent with > the data on disk: > > cpu1 cpu2 > ------------------------------|------------------------------ > // Buffered write 2048 from 0 > ext4_buffered_write_iter > generic_perform_write > copy_page_from_iter_atomic > ext4_da_write_end > ext4_da_do_write_end > block_write_end > __block_commit_write > folio_mark_uptodate > // Buffered read 4096 from 0 smp_wmb() > ext4_file_read_iter set_bit(PG_uptodate, folio_flags) > generic_file_read_iter i_size_write // 2048 > filemap_read unlock_page(page) > filemap_get_pages > filemap_get_read_batch > folio_test_uptodate(folio) > ret = test_bit(PG_uptodate, folio_flags) > if (ret) > smp_rmb(); > // Ensure that the data in page 0-2048 is up-to-date. > > // New buffered write 2048 from 2048 > ext4_buffered_write_iter > generic_perform_write > copy_page_from_iter_atomic > ext4_da_write_end > ext4_da_do_write_end > block_write_end > __block_commit_write > folio_mark_uptodate > smp_wmb() > set_bit(PG_uptodate, folio_flags) > i_size_write // 4096 > unlock_page(page) > > isize = i_size_read(inode) // 4096 > // Read the latest isize 4096, but without smp_rmb(), there may be > // Load-Load disorder resulting in the data in the 2048-4096 range > // in the page is not up-to-date. > copy_page_to_iter > // copyout 4096 > > In the concurrency above, we read the updated i_size, but there is no read > barrier to ensure that the data in the page is the same as the i_size at > this point, so we may copy the unsynchronized page out. Hence adding the > missing read memory barrier to fix this. > > This is a Load-Load reordering issue, which only occurs on some weak > mem-ordering architectures (e.g. ARM64, ALPHA), but not on strong > mem-ordering architectures (e.g. X86). And theoretically the problem AFAIK x86 can also reorder loads vs loads so the problem can in theory happen on x86 as well. > doesn't only happen on ext4, filesystems that call filemap_read() but > don't hold inode lock (e.g. btrfs, f2fs, ubifs ...) will have this > problem, while filesystems with inode lock (e.g. xfs, nfs) won't have > this problem. > > Cc: stable@kernel.org > Signed-off-by: Baokun Li > --- > mm/filemap.c | 3 +++ > 1 file changed, 3 insertions(+) > > diff --git a/mm/filemap.c b/mm/filemap.c > index 71f00539ac00..6324e2ac3e74 100644 > --- a/mm/filemap.c > +++ b/mm/filemap.c > @@ -2607,6 +2607,9 @@ ssize_t filemap_read(struct kiocb *iocb, struct iov_iter *iter, > goto put_folios; > end_offset = min_t(loff_t, isize, iocb->ki_pos + iter->count); > > + /* Ensure that the page cache within isize is updated. */ Barries have to be in pairs to work and it is a good practice to document this. So here I'd have comment like: /* * Pairs with a barrier in * block_write_end()->mark_buffer_dirty() or other page * dirtying routines like iomap_write_end() to ensure * changes to page contents are visible before we see * increased inode size. */ Honza > + smp_rmb(); > + > /* > * Once we start copying data, we don't want to be touching any > * cachelines that might be contended: > -- > 2.31.1 > -- Jan Kara SUSE Labs, CR