From patchwork Wed Apr 9 13:09:40 2025 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Christoph Hellwig X-Patchwork-Id: 14044570 Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (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 9E1D225F991 for ; Wed, 9 Apr 2025 13:09:45 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=198.137.202.133 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1744204187; cv=none; b=taFBA4kYYm5F3+x2LFVhlJDro4HwzZSB+DMNFAr+mPPPOZ0mgt04mYk10D3SgRZRfHJO7y2vcSks0jVzie/AHQMLS8JzEJYigd6Tcem/FSZw78Jqb6yXOZOnAiTDshxWXiWn6jKAkOBLnFVf31FFM2BpDQQqi44hSSMJzL+pR0o= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1744204187; c=relaxed/simple; bh=OWZUUf6RmdhJj0xw63vvxYlk3DIOBGH3jVGYjBMx3/c=; h=From:To:Cc:Subject:Date:Message-ID:MIME-Version; b=TIYqKu2POjM66F6Q5pWoRqlzcrXrROsdPRTPgCAw3LVnYGzHWduwspDTDYrPc6KigTSc7MTlUcrR+HEruxn7EA9M662CA/0Ypm27Z9yPob3MKjxVq0ffwl3bAIHOInv6etvAd3KmKVGAP28/IpqreiDO4iIhbQBObnSMABz3Ats= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=fail (p=none dis=none) header.from=lst.de; spf=none smtp.mailfrom=bombadil.srs.infradead.org; dkim=pass (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b=tRCiJlmK; arc=none smtp.client-ip=198.137.202.133 Authentication-Results: smtp.subspace.kernel.org; dmarc=fail (p=none dis=none) header.from=lst.de Authentication-Results: smtp.subspace.kernel.org; spf=none smtp.mailfrom=bombadil.srs.infradead.org Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b="tRCiJlmK" DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=bombadil.20210309; h=Content-Transfer-Encoding: MIME-Version:Message-ID:Date:Subject:Cc:To:From:Sender:Reply-To:Content-Type: Content-ID:Content-Description:In-Reply-To:References; bh=xEBbC7SwkA5EPzU+0FdhiAqp8AX7jj0UYBAgxF7dfSY=; b=tRCiJlmKWm4AhIz+DUrk4cpFg1 KLzbFTQMBJYUdvK0Jbe43c0kJAa3R7OSiWFvdmZ8GYnTuvoQTxG5EjYQQHSPwgvwoxc+M72GGpGTs Jci0btsoLrFlM+9mKTyWLjgTdBsDYlb6TMLvqgyVZUk9hMVCZLN6WviQKlDC68gW3k9sbXXzc1SvX /dWBg9ZF0W1AKOuUq6edUY69vd0JDokW3R3ytY2zCzJ2or1Gw3JM21mh8yy7k99Zi4lSRhSI+a3Wu 7se1JkRDn8LrwW+vXH8FJRtDPdYFFQmkGoaqxqJJNGIkTVoT0kGYzfcki6bh+CZ1g3nAD6FT97i69 YMfNt4Ww==; Received: from [2001:4bb8:2d1:7d59:587c:5e75:3ec0:23ae] (helo=localhost) by bombadil.infradead.org with esmtpsa (Exim 4.98.2 #2 (Red Hat Linux)) id 1u2VBY-00000007Eix-1rzt; Wed, 09 Apr 2025 13:09:44 +0000 From: Christoph Hellwig To: axboe@kernel.dk Cc: djwong@kernel.org, linux-block@vger.kernel.org, ming.lei@redhat.com Subject: [PATCH] loop: stop using vfs_iter_{read,write} for buffered I/O Date: Wed, 9 Apr 2025 15:09:40 +0200 Message-ID: <20250409130940.3685677-1-hch@lst.de> X-Mailer: git-send-email 2.47.2 Precedence: bulk X-Mailing-List: linux-block@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-SRS-Rewrite: SMTP reverse-path rewritten from by bombadil.infradead.org. See http://www.infradead.org/rpr.html vfs_iter_{read,write} always perform direct I/O when the file has the O_DIRECT flag set, which breaks disabling direct I/O using the LOOP_SET_STATUS / LOOP_SET_STATUS64 ioctls. This was recenly reported as a regression, but as far as I can tell was only uncovered by better checking for block sizes and has been around since the direct I/O support was added. Fix this by using the existing aio code that calls the raw read/write iter methods instead. Note that despite the comments there is no need for block drivers to ever call flush_dcache_page themselves, and the call is a left-over from prehistoric times. Fixes: ab1cb278bc70 ("block: loop: introduce ioctl command of LOOP_SET_DIRECT_IO") Reported-by: Darrick J. Wong Signed-off-by: Christoph Hellwig Reviewed-by: Ming Lei Tested-by: "Darrick J. Wong" --- drivers/block/loop.c | 112 +++++++------------------------------------ 1 file changed, 17 insertions(+), 95 deletions(-) diff --git a/drivers/block/loop.c b/drivers/block/loop.c index 674527d770dc..0e925f1642cc 100644 --- a/drivers/block/loop.c +++ b/drivers/block/loop.c @@ -211,72 +211,6 @@ static void loop_set_size(struct loop_device *lo, loff_t size) kobject_uevent(&disk_to_dev(lo->lo_disk)->kobj, KOBJ_CHANGE); } -static int lo_write_bvec(struct file *file, struct bio_vec *bvec, loff_t *ppos) -{ - struct iov_iter i; - ssize_t bw; - - iov_iter_bvec(&i, ITER_SOURCE, bvec, 1, bvec->bv_len); - - bw = vfs_iter_write(file, &i, ppos, 0); - - if (likely(bw == bvec->bv_len)) - return 0; - - printk_ratelimited(KERN_ERR - "loop: Write error at byte offset %llu, length %i.\n", - (unsigned long long)*ppos, bvec->bv_len); - if (bw >= 0) - bw = -EIO; - return bw; -} - -static int lo_write_simple(struct loop_device *lo, struct request *rq, - loff_t pos) -{ - struct bio_vec bvec; - struct req_iterator iter; - int ret = 0; - - rq_for_each_segment(bvec, rq, iter) { - ret = lo_write_bvec(lo->lo_backing_file, &bvec, &pos); - if (ret < 0) - break; - cond_resched(); - } - - return ret; -} - -static int lo_read_simple(struct loop_device *lo, struct request *rq, - loff_t pos) -{ - struct bio_vec bvec; - struct req_iterator iter; - struct iov_iter i; - ssize_t len; - - rq_for_each_segment(bvec, rq, iter) { - iov_iter_bvec(&i, ITER_DEST, &bvec, 1, bvec.bv_len); - len = vfs_iter_read(lo->lo_backing_file, &i, &pos, 0); - if (len < 0) - return len; - - flush_dcache_page(bvec.bv_page); - - if (len != bvec.bv_len) { - struct bio *bio; - - __rq_for_each_bio(bio, rq) - zero_fill_bio(bio); - break; - } - cond_resched(); - } - - return 0; -} - static void loop_clear_limits(struct loop_device *lo, int mode) { struct queue_limits lim = queue_limits_start_update(lo->lo_queue); @@ -342,7 +276,7 @@ static void lo_complete_rq(struct request *rq) struct loop_cmd *cmd = blk_mq_rq_to_pdu(rq); blk_status_t ret = BLK_STS_OK; - if (!cmd->use_aio || cmd->ret < 0 || cmd->ret == blk_rq_bytes(rq) || + if (cmd->ret < 0 || cmd->ret == blk_rq_bytes(rq) || req_op(rq) != REQ_OP_READ) { if (cmd->ret < 0) ret = errno_to_blk_status(cmd->ret); @@ -358,14 +292,13 @@ static void lo_complete_rq(struct request *rq) cmd->ret = 0; blk_mq_requeue_request(rq, true); } else { - if (cmd->use_aio) { - struct bio *bio = rq->bio; + struct bio *bio = rq->bio; - while (bio) { - zero_fill_bio(bio); - bio = bio->bi_next; - } + while (bio) { + zero_fill_bio(bio); + bio = bio->bi_next; } + ret = BLK_STS_IOERR; end_io: blk_mq_end_request(rq, ret); @@ -445,9 +378,14 @@ static int lo_rw_aio(struct loop_device *lo, struct loop_cmd *cmd, cmd->iocb.ki_pos = pos; cmd->iocb.ki_filp = file; - cmd->iocb.ki_complete = lo_rw_aio_complete; - cmd->iocb.ki_flags = IOCB_DIRECT; cmd->iocb.ki_ioprio = IOPRIO_PRIO_VALUE(IOPRIO_CLASS_NONE, 0); + if (cmd->use_aio) { + cmd->iocb.ki_complete = lo_rw_aio_complete; + cmd->iocb.ki_flags = IOCB_DIRECT; + } else { + cmd->iocb.ki_complete = NULL; + cmd->iocb.ki_flags = 0; + } if (rw == ITER_SOURCE) ret = file->f_op->write_iter(&cmd->iocb, &iter); @@ -458,7 +396,7 @@ static int lo_rw_aio(struct loop_device *lo, struct loop_cmd *cmd, if (ret != -EIOCBQUEUED) lo_rw_aio_complete(&cmd->iocb, ret); - return 0; + return -EIOCBQUEUED; } static int do_req_filebacked(struct loop_device *lo, struct request *rq) @@ -466,15 +404,6 @@ static int do_req_filebacked(struct loop_device *lo, struct request *rq) struct loop_cmd *cmd = blk_mq_rq_to_pdu(rq); loff_t pos = ((loff_t) blk_rq_pos(rq) << 9) + lo->lo_offset; - /* - * lo_write_simple and lo_read_simple should have been covered - * by io submit style function like lo_rw_aio(), one blocker - * is that lo_read_simple() need to call flush_dcache_page after - * the page is written from kernel, and it isn't easy to handle - * this in io submit style function which submits all segments - * of the req at one time. And direct read IO doesn't need to - * run flush_dcache_page(). - */ switch (req_op(rq)) { case REQ_OP_FLUSH: return lo_req_flush(lo, rq); @@ -490,15 +419,9 @@ static int do_req_filebacked(struct loop_device *lo, struct request *rq) case REQ_OP_DISCARD: return lo_fallocate(lo, rq, pos, FALLOC_FL_PUNCH_HOLE); case REQ_OP_WRITE: - if (cmd->use_aio) - return lo_rw_aio(lo, cmd, pos, ITER_SOURCE); - else - return lo_write_simple(lo, rq, pos); + return lo_rw_aio(lo, cmd, pos, ITER_SOURCE); case REQ_OP_READ: - if (cmd->use_aio) - return lo_rw_aio(lo, cmd, pos, ITER_DEST); - else - return lo_read_simple(lo, rq, pos); + return lo_rw_aio(lo, cmd, pos, ITER_DEST); default: WARN_ON_ONCE(1); return -EIO; @@ -1921,7 +1844,6 @@ static void loop_handle_cmd(struct loop_cmd *cmd) struct loop_device *lo = rq->q->queuedata; int ret = 0; struct mem_cgroup *old_memcg = NULL; - const bool use_aio = cmd->use_aio; if (write && (lo->lo_flags & LO_FLAGS_READ_ONLY)) { ret = -EIO; @@ -1951,7 +1873,7 @@ static void loop_handle_cmd(struct loop_cmd *cmd) } failed: /* complete non-aio request */ - if (!use_aio || ret) { + if (ret != -EIOCBQUEUED) { if (ret == -EOPNOTSUPP) cmd->ret = ret; else