From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (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 3BC27560AD7; Tue, 8 Sep 2026 16:34:49 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1788885290; cv=none; b=UJZL6kFqia7c66sQVNOKtQgT2cm3DAQ6zkmaRNbVFPthOYXyTG7H1VUfB5LdlQ2Uk3SDTgWaPhZlkzlNKS0OhZotTf+iTYEO1tzFqLz+C+3W2ZrAyA5rLA+eEleIhMBOWx+ELcoZj3xc4v14E4JroihxV8N0PsMeSWVtbbUWj6A= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1788885290; c=relaxed/simple; bh=tGu/gKn3bAhi5s7Tl/toqEb6jcrVVQoi6O83bRyx9S0=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=Po8fRqpfotwP6BOqjboSY1hG3rgxGcBoFqnPEKGhGACfjh1PibzFCmaHetlWjzGVqLzWrI0z0yYK9mApgfmm0u6QVF5BU59RgfzYxIirc3uixRYIZNZr3mniicZ5oXNrLlnVxLJMAaC4AxbXvsCv8poP6onIHST9ngcjH39H/KI= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=nWRFSWrc; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="nWRFSWrc" Received: by smtp.kernel.org (Postfix) with ESMTPSA id D59AB1F00A3E; Tue, 8 Sep 2026 16:34:48 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1788885289; bh=xsarEBQz83oy13kJ3SZ3R6K9bssRVn1ez842Rktmuhs=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=nWRFSWrcX2wzyvITPe5chEehHKwUI/2PqzKTcBnludgpOOa0Udq44AU3tv1d4MJVO FNjopdZewMXVeqp30uuGVoH/B5uR1VZVj2KWFnVQQ0qoz2+WGy7OsGIorZS6FvRJGT c4y8ya8UzV+xellXwG5ad4gcGgYxhCR260ywrw0WoYOEvMDQupso3WzVJNbT+9Q7aZ tBxNGl15FHEelLZOhASO+m/Hc2HIpmZR3ifQ7QJSqCtmoDjPYZ0sTqDcwXtgsIym7e zGEAmo52U4N8qTtZs8o/OMYSREkb0X+72JLP5HYkAL4y7EYjrdLQo/lEjYw3G+5uIx FAWtnWti7ZAAQ== From: Mike Snitzer To: linux-nfs@vger.kernel.org, linux-block@vger.kernel.org Cc: dm-devel@lists.linux.dev, axboe@kernel.dk, cel@kernel.org, jlayton@kernel.org, david.flynn@hammerspace.com Subject: [PATCH 0/4] block, nfsd: fixes for sub-sector bvec direct I/O Date: Tue, 8 Sep 2026 12:34:35 -0400 Message-ID: <20260908163448.30841-1-snitzer@kernel.org> X-Mailer: git-send-email 2.44.0 In-Reply-To: <20260908163232.30774-1-snitzer@kernel.org> References: <20260908163232.30774-1-snitzer@kernel.org> Precedence: bulk X-Mailing-List: linux-nfs@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit While qualifying NFSD's NFSD_IO_DIRECT write path with byte-level data verification, it was found that the ITER_BVEC payloads nfsd submits expose silent data corruption in two bio-based block drivers and two defects in nfsd itself. Example problematic payloads is the first fragment starts mid-page because the RPC header precedes it in the receive buffer, and fragment lengths need not be sector multiples. bio_iov_bvec_set() passes such an array to the queue as-is; nothing below it validates per-bvec sector alignment. Patches 1-2 fix silent corruption (write completes successfully, data lands wrong) and are stable candidates: - brd re-derives each segment's device position from bio->bi_iter.bi_sector, which bio_advance_iter_single() advances by whole sectors only, so a sub-sector segment length skews everything that follows. - zram hardwires is_partial_io() to false on 4K-page kernels, sending sub-page bvecs down a whole-page path that ignores bv_offset/bv_len entirely, and has the same sector-cursor skew. Both are verified with a synthetic-bio reproducer (stamped pattern, write, read back, compare) across mid-page and page-aligned geometries. Patches 3-4 fix nfsd: the filecache never fetches DIO alignment attributes on the supplied-file acquire branch, so every WRITE to a file created via NFSv4 OPEN(CREATE) is refused direct I/O for the file's cached lifetime; and nfsd's statx-based DIO gate is weaker than bio_split_io_at()'s split-time checks, so an admitted iterator can still be rejected by the block layer -- retry the segment buffered instead of failing a valid WRITE with NFS4ERR_INVAL. One open question for the iomap/block maintainers: should ITER_BVEC direct I/O with sub-sector bvec boundaries be validated or bounced centrally rather than trusted to every driver's iteration? An audit of in-tree bio-based drivers found the same bi_sector-derived position pattern in dm-io, dm-log-writes, dm-writecache (pmem path) and dm-integrity -- unreachable through nfsd today only because dm queues advertise dma_alignment >= 511, which nfsd's alignment gate refuses. Tested with the reproducer matrix on brd, zram and nvme-loop at 4K and 16K page size (aarch64) and 4K (x86_64), plus 30-connection NFS write rigs comparing source against export byte-for-byte: clean with the fixes, corrupting or erroring without them. Mike Snitzer (3): brd: iterate the bio by byte position, not bi_sector zram: handle sub-page bvec segments without corrupting data nfsd: fall back to buffered I/O when a direct write gets -EINVAL David Flynn (1): nfsd: fetch direct I/O alignment for files handed to the filecache drivers/block/brd.c | 29 +++++++++++++++++++++++------ drivers/block/zram/zram_drv.c | 36 +++++++++++++++++------------------ fs/nfsd/filecache.c | 4 ++-- fs/nfsd/vfs.c | 29 +++++++++++++++++++++++++++++ 4 files changed, 77 insertions(+), 31 deletions(-) -- 2.52.0