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block: properly handle IOCB_NOWAIT for async O_DIRECT IO 

A caller is supposed to pass in REQ_NOWAIT if we can't block for any
given operation, but O_DIRECT for block devices just ignore this. Hence
we'll block for various resource shortages on the block layer side,
like having to wait for requests.

Use the new REQ_NOWAIT_INLINE to ask for this error to be returned
inline, so we can handle it appropriately and return -EAGAIN to the
caller.

Signed-off-by: Jens Axboe <axboe@kernel.dk>
This commit is contained in:
Jens Axboe 2019-07-16 13:56:42 -06:00
parent 893a1c9720
commit 6a43074e2f
1 changed files with 50 additions and 8 deletions
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58
fs/block_dev.c
View File

@ -344,15 +344,24 @@ __blkdev_direct_IO(struct kiocb *iocb, struct iov_iter *iter, int nr_pages)
struct bio *bio;
bool is_poll = (iocb->ki_flags & IOCB_HIPRI) != 0;
bool is_read = (iov_iter_rw(iter) == READ), is_sync;
bool nowait = (iocb->ki_flags & IOCB_NOWAIT) != 0;
loff_t pos = iocb->ki_pos;
blk_qc_t qc = BLK_QC_T_NONE;
int ret = 0;
gfp_t gfp;
ssize_t ret;
if ((pos | iov_iter_alignment(iter)) &
(bdev_logical_block_size(bdev) - 1))
return -EINVAL;
bio = bio_alloc_bioset(GFP_KERNEL, nr_pages, &blkdev_dio_pool);
if (nowait)
gfp = GFP_NOWAIT;
else
gfp = GFP_KERNEL;
bio = bio_alloc_bioset(gfp, nr_pages, &blkdev_dio_pool);
if (!bio)
return -EAGAIN;
dio = container_of(bio, struct blkdev_dio, bio);
dio->is_sync = is_sync = is_sync_kiocb(iocb);
@ -374,7 +383,10 @@ __blkdev_direct_IO(struct kiocb *iocb, struct iov_iter *iter, int nr_pages)
if (!is_poll)
blk_start_plug(&plug);
ret = 0;
for (;;) {
int err;
bio_set_dev(bio, bdev);
bio->bi_iter.bi_sector = pos >> 9;
bio->bi_write_hint = iocb->ki_hint;
@ -382,8 +394,10 @@ __blkdev_direct_IO(struct kiocb *iocb, struct iov_iter *iter, int nr_pages)
bio->bi_end_io = blkdev_bio_end_io;
bio->bi_ioprio = iocb->ki_ioprio;
ret = bio_iov_iter_get_pages(bio, iter);
if (unlikely(ret)) {
err = bio_iov_iter_get_pages(bio, iter);
if (unlikely(err)) {
if (!ret)
ret = err;
bio->bi_status = BLK_STS_IOERR;
bio_endio(bio);
break;
@ -398,6 +412,14 @@ __blkdev_direct_IO(struct kiocb *iocb, struct iov_iter *iter, int nr_pages)
task_io_account_write(bio->bi_iter.bi_size);
}
/*
* Tell underlying layer to not block for resource shortage.
* And if we would have blocked, return error inline instead
* of through the bio->bi_end_io() callback.
*/
if (nowait)
bio->bi_opf |= (REQ_NOWAIT | REQ_NOWAIT_INLINE);
dio->size += bio->bi_iter.bi_size;
pos += bio->bi_iter.bi_size;
@ -411,6 +433,11 @@ __blkdev_direct_IO(struct kiocb *iocb, struct iov_iter *iter, int nr_pages)
}
qc = submit_bio(bio);
if (qc == BLK_QC_T_EAGAIN) {
if (!ret)
ret = -EAGAIN;
goto error;
}
if (polled)
WRITE_ONCE(iocb->ki_cookie, qc);
@ -431,8 +458,20 @@ __blkdev_direct_IO(struct kiocb *iocb, struct iov_iter *iter, int nr_pages)
atomic_inc(&dio->ref);
}
submit_bio(bio);
bio = bio_alloc(GFP_KERNEL, nr_pages);
qc = submit_bio(bio);
if (qc == BLK_QC_T_EAGAIN) {
if (!ret)
ret = -EAGAIN;
goto error;
}
ret += bio->bi_iter.bi_size;
bio = bio_alloc(gfp, nr_pages);
if (!bio) {
if (!ret)
ret = -EAGAIN;
goto error;
}
}
if (!is_poll)
@ -452,13 +491,16 @@ __blkdev_direct_IO(struct kiocb *iocb, struct iov_iter *iter, int nr_pages)
}
__set_current_state(TASK_RUNNING);
out:
if (!ret)
ret = blk_status_to_errno(dio->bio.bi_status);
if (likely(!ret))
ret = dio->size;
bio_put(&dio->bio);
return ret;
error:
if (!is_poll)
blk_finish_plug(&plug);
goto out;
}
static ssize_t