mirror of https://github.com/hak5/openwrt.git
kernel: add promising "fix loop discard errors" hack
This patch adds a promising upstream patch that claims to help for the treated I/O errors happening on f2fs or ext4 on real block devices. |print_req_error: I/O error, dev loop1, sector 1334 Link: <https://patchwork.kernel.org/cover/10931787/> Signed-off-by: Christian Lamparter <chunkeey@gmail.com>master
Christian Lamparter
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From: Evan Green <evgreen@chromium.org>
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Subject: [PATCH v5 0/2] loop: Better discard for block devices
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Date: Mon, 6 May 2019 11:27:35 -0700
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Message-Id: <20190506182736.21064-2-evgreen@chromium.org>
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This series addresses some errors seen when using the loop
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device directly backed by a block device.
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The first change titled "loop: Better discard for block devices"
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plumbs out the correct error message, and the second change prevents
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the error from occurring in many cases.
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The errors look like this:
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[ 90.880875] print_req_error: I/O error, dev loop5, sector 0
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The errors occur when trying to do a discard or write zeroes operation
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on a loop device backed by a block device that does not support write zeroes.
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Firstly, the error itself is incorrectly reported as I/O error, but is
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actually EOPNOTSUPP. The first patch plumbs out EOPNOTSUPP to properly
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report the error.
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The second patch called "loop: Better discard support for block devices"
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prevents these errors from occurring by mirroring the zeroing capabilities
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of the underlying block device into the loop device.
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Before this change, discard was always reported as being supported, and
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the loop device simply turns around and does an fallocate operation on the
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backing device. After this change, backing block devices that do support
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zeroing will continue to work as before, and continue to get all the
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benefits of doing that. Backing devices that do not support zeroing will
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fail earlier, avoiding hitting the loop device at all and ultimately
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avoiding this error in the logs.
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I can also confirm that this fixes test block/003 in the blktests, when
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running blktests on a loop device backed by a block device.
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Signed-off-by: Evan Green <evgreen@chromium.org>
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Reviewed-by: Ming Lei <ming.lei@redhat.com>
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Reviewed-by: Bart Van Assche <bvanassche@acm.org>
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Reviewed-by: Martin K. Petersen <martin.petersen@oracle.com>
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Reviewed-by: Gwendal Grignou <gwendal@chromium.org>
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Reviewed-by: Chaitanya Kulkarni <chaitanya.kulkarni@wdc.com>
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---
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--- a/drivers/block/loop.c
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+++ b/drivers/block/loop.c
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@@ -416,19 +416,14 @@ out_free_page:
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return ret;
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}
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-static int lo_discard(struct loop_device *lo, struct request *rq, loff_t pos)
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+static int lo_discard(struct loop_device *lo, struct request *rq,
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+ int mode, loff_t pos)
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{
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- /*
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- * We use punch hole to reclaim the free space used by the
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- * image a.k.a. discard. However we do not support discard if
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- * encryption is enabled, because it may give an attacker
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- * useful information.
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- */
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struct file *file = lo->lo_backing_file;
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- int mode = FALLOC_FL_PUNCH_HOLE | FALLOC_FL_KEEP_SIZE;
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+ struct request_queue *q = lo->lo_queue;
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int ret;
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- if ((!file->f_op->fallocate) || lo->lo_encrypt_key_size) {
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+ if (!blk_queue_discard(q)) {
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ret = -EOPNOTSUPP;
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goto out;
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}
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@@ -457,7 +452,9 @@ static void lo_complete_rq(struct reques
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if (!cmd->use_aio || cmd->ret < 0 || cmd->ret == blk_rq_bytes(rq) ||
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req_op(rq) != REQ_OP_READ) {
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- if (cmd->ret < 0)
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+ if (cmd->ret == -EOPNOTSUPP)
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+ ret = BLK_STS_NOTSUPP;
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+ else if (cmd->ret < 0)
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ret = BLK_STS_IOERR;
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goto end_io;
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}
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@@ -597,8 +594,13 @@ static int do_req_filebacked(struct loop
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case REQ_OP_FLUSH:
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return lo_req_flush(lo, rq);
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case REQ_OP_DISCARD:
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+ return lo_discard(lo, rq,
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+ FALLOC_FL_PUNCH_HOLE | FALLOC_FL_KEEP_SIZE, pos);
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+
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case REQ_OP_WRITE_ZEROES:
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- return lo_discard(lo, rq, pos);
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+ return lo_discard(lo, rq,
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+ FALLOC_FL_ZERO_RANGE | FALLOC_FL_KEEP_SIZE, pos);
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+
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case REQ_OP_WRITE:
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if (lo->transfer)
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return lo_write_transfer(lo, rq, pos);
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@@ -853,6 +855,21 @@ static void loop_config_discard(struct l
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struct file *file = lo->lo_backing_file;
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struct inode *inode = file->f_mapping->host;
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struct request_queue *q = lo->lo_queue;
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+ struct request_queue *backingq;
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+
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+ /*
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+ * If the backing device is a block device, mirror its zeroing
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+ * capability. REQ_OP_DISCARD translates to a zero-out even when backed
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+ * by block devices to keep consistent behavior with file-backed loop
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+ * devices.
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+ */
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+ if (S_ISBLK(inode->i_mode) && !lo->lo_encrypt_key_size) {
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+ backingq = bdev_get_queue(inode->i_bdev);
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+ blk_queue_max_discard_sectors(q,
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+ backingq->limits.max_write_zeroes_sectors);
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+
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+ blk_queue_max_write_zeroes_sectors(q,
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+ backingq->limits.max_write_zeroes_sectors);
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/*
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* We use punch hole to reclaim the free space used by the
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@@ -860,22 +877,24 @@ static void loop_config_discard(struct l
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* encryption is enabled, because it may give an attacker
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* useful information.
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*/
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- if ((!file->f_op->fallocate) ||
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- lo->lo_encrypt_key_size) {
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+ } else if ((!file->f_op->fallocate) || lo->lo_encrypt_key_size) {
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q->limits.discard_granularity = 0;
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q->limits.discard_alignment = 0;
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blk_queue_max_discard_sectors(q, 0);
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blk_queue_max_write_zeroes_sectors(q, 0);
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- blk_queue_flag_clear(QUEUE_FLAG_DISCARD, q);
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- return;
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- }
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- q->limits.discard_granularity = inode->i_sb->s_blocksize;
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- q->limits.discard_alignment = 0;
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+ } else {
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+ q->limits.discard_granularity = inode->i_sb->s_blocksize;
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+ q->limits.discard_alignment = 0;
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- blk_queue_max_discard_sectors(q, UINT_MAX >> 9);
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- blk_queue_max_write_zeroes_sectors(q, UINT_MAX >> 9);
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- blk_queue_flag_set(QUEUE_FLAG_DISCARD, q);
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+ blk_queue_max_discard_sectors(q, UINT_MAX >> 9);
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+ blk_queue_max_write_zeroes_sectors(q, UINT_MAX >> 9);
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+ }
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+
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+ if (q->limits.max_write_zeroes_sectors)
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+ blk_queue_flag_set(QUEUE_FLAG_DISCARD, q);
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+ else
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+ blk_queue_flag_clear(QUEUE_FLAG_DISCARD, q);
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}
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static void loop_unprepare_queue(struct loop_device *lo)
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@@ -1893,7 +1912,10 @@ static void loop_handle_cmd(struct loop_
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failed:
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/* complete non-aio request */
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if (!cmd->use_aio || ret) {
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- cmd->ret = ret ? -EIO : 0;
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+ if (ret == -EOPNOTSUPP)
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+ cmd->ret = ret;
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+ else
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+ cmd->ret = ret ? -EIO : 0;
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blk_mq_complete_request(rq);
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}
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}
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