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loop: stop using vfs_iter_{read,write} for buffered I/O

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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 <djwong@kernel.org>
Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Ming Lei <ming.lei@redhat.com>
Tested-by: Darrick J. Wong <djwong@kernel.org>
Link: https://lore.kernel.org/r/20250409130940.3685677-1-hch@lst.de
Signed-off-by: Jens Axboe <axboe@kernel.dk>
This commit is contained in:
Christoph Hellwig 2025-04-09 15:09:40 +02:00 committed by Jens Axboe
parent 0dba7a05b9
commit f2fed441c6
1 changed files with 17 additions and 95 deletions
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112
drivers/block/loop.c
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@ -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 = req_get_ioprio(rq);
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;
@ -1922,7 +1845,6 @@ 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;
@ -1952,7 +1874,7 @@ 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