From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 9D4152571C9; Tue, 24 Jun 2025 20:25:43 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1750796743; cv=none; b=KvMN2vBCg3O0nsJihqi5GbmPaoDldT06fIgO6sNLtQXjqzVFwHTzxCUDjL7jIblD0swA8Q+7BU6WULwnlkOszGoVabfeQB3MQRIR2Yt1iUCSk3bpw800QLv7sqI5Oa5S7Hqorq8Fcm+uvnzEo7sADYPFBSBNKUjKysn+z+Ov1d0= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1750796743; c=relaxed/simple; bh=D7CPEpx1S67e7eDiNevj8fbmWkAah/k4UBwRiV31iiE=; h=Message-ID:Subject:From:To:Cc:Date:In-Reply-To:References: Content-Type:MIME-Version; b=qIxnbZcVI7U5VSDlGCP+jKNKEpzs1eP2lusNmXEIl6Dk0fouRpVK2+wYgHRSnUA2AJxgeIDOYFo4n1TPmobrfgJQ/5rX7lGtvSUkiJATmn54y97zCaqQZQJdWw9fEbyakIjTCJVNNV1pcDc/tWbH6qZQFqrCwqVLSn6MAfoNQ84= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=rw+fNrmY; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="rw+fNrmY" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 5E48EC4CEE3; Tue, 24 Jun 2025 20:25:42 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1750796743; bh=D7CPEpx1S67e7eDiNevj8fbmWkAah/k4UBwRiV31iiE=; h=Subject:From:To:Cc:Date:In-Reply-To:References:From; b=rw+fNrmYUq7BG6c8/CrN4jU6x+qttjslxJaRpQA+VeMjyaq/59m3d0/yxPZPW+8t7 AaSxIJbYK1zGXs9J17H2ihg63leg8HpFa6atQqJxdP8UTgAEg12WGGednfQQ7Rcg0R cScgvSzfmxo0PfZXzKVGskwGprzRzJQKXI8zEW+eaxI9LegniL++BQ3bLrkGHO+bHB nZ6Q3G6KMxRzj/PbLeoQqr7ETr/3UJ3lwnOWzaBD72bKd+kcNWHzU/cS6PSbgE1rw/ HdZzOYikfSCok64mdN5ec96lD5DQsMDnRGjI+swqVRGWyvHmfKt2VgpQ7jsksgJdSf OFbQmksisB5Pg== Message-ID: Subject: Re: [PATCH] xfs: report a writeback error on a read() call From: Jeff Layton To: Matthew Wilcox Cc: Christoph Hellwig , ying chen , djwong@kernel.org, linux-xfs@vger.kernel.org, linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org Date: Tue, 24 Jun 2025 16:25:41 -0400 In-Reply-To: References: Autocrypt: addr=jlayton@kernel.org; prefer-encrypt=mutual; keydata=mQINBE6V0TwBEADXhJg7s8wFDwBMEvn0qyhAnzFLTOCHooMZyx7XO7dAiIhDSi7G1NPxw n8jdFUQMCR/GlpozMFlSFiZXiObE7sef9rTtM68ukUyZM4pJ9l0KjQNgDJ6Fr342Htkjxu/kFV1Wv egyjnSsFt7EGoDjdKqr1TS9syJYFjagYtvWk/UfHlW09X+jOh4vYtfX7iYSx/NfqV3W1D7EDi0PqV T2h6v8i8YqsATFPwO4nuiTmL6I40ZofxVd+9wdRI4Db8yUNA4ZSP2nqLcLtFjClYRBoJvRWvsv4lm 0OX6MYPtv76hka8lW4mnRmZqqx3UtfHX/hF/zH24Gj7A6sYKYLCU3YrI2Ogiu7/ksKcl7goQjpvtV YrOOI5VGLHge0awt7bhMCTM9KAfPc+xL/ZxAMVWd3NCk5SamL2cE99UWgtvNOIYU8m6EjTLhsj8sn 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chen wrote: > > > > Normally, user space returns immediately after writing data to the > > > > buffer cache. However, if an error occurs during the actual disk > > > > write operation, data loss may ensue, and there is no way to report > > > > this error back to user space immediately. Current kernels may repo= rt > > > > writeback errors when fsync() is called, but frequent invocations o= f > > > > fsync() can degrade performance. Therefore, a new sysctl > > > > fs.xfs.report_writeback_error_on_read is introduced, which, when se= t > > > > to 1, reports writeback errors when read() is called. This allows u= ser > > > > space to be notified of writeback errors more promptly. > > >=20 > > > That's really kernel wide policy and not something magic done by a > > > single file system. > >=20 > > ...not to mention that getting an error back on a read for a prior > > writeback error would be completely unexpected by most applications. >=20 > Well. It's somewhat understandable: >=20 > write() (returns success) > writeback happens, error logged > memory pressure evicts folio > read() brings folio into page cache > attempt to read contents fails, error returned >=20 > I'm not sure it's a good solution, but it's plausible. Personally, I find it confusing. The range you're trying to read might actually be fine if the error happened in a different range. It also has the same problem as reporting writeback errors on close(), in that it's non-deterministic. You might not see an error if writeback didn't happen yet. Just because you didn't get an error when reading, that doesn't mean that your data is actually safe. Maybe this is ok as an opt-in thing for some workloads, but it does have some potential footguns. --=20 Jeff Layton