[PATCH 18/20] block: refator submit_bio_noacct

Christoph Hellwig
2020-06-29T19:47:11Z

Split out a __submit_bio_noacct helper for the actual de-recursion
algorithm, and simplify the loop by using a continue when we can't
enter the queue for a bio.

Signed-off-by: Christoph Hellwig <hch@lst.de>
---
block/blk-core.c | 131 +++++++++++++++++++++++++----------------------
1 file changed, 71 insertions(+), 60 deletions(-)

diff --git a/block/blk-core.c b/block/blk-core.c
index 1caeb01e127768..b82f48c86e6f7a 100644
--- a/block/blk-core.c
+++ b/block/blk-core.c
@@ -1085,6 +1085,74 @@ static blk_qc_t do_make_request(struct bio *bio)
return ret;
}

+/*
+ * The loop in this function may be a bit non-obvious, and so deserves some
+ * explanation:
+ *
+ * - Before entering the loop, bio->bi_next is NULL (as all callers ensure
+ * that), so we have a list with a single bio.
+ * - We pretend that we have just taken it off a longer list, so we assign
+ * bio_list to a pointer to the bio_list_on_stack, thus initialising the
+ * bio_list of new bios to be added. ->submit_bio() may indeed add some more
+ * bios through a recursive call to submit_bio_noacct. If it did, we find a
+ * non-NULL value in bio_list and re-enter the loop from the top.
+ * - In this case we really did just take the bio of the top of the list (no
+ * pretending) and so remove it from bio_list, and call into ->submit_bio()
+ * again.
+ *
+ * bio_list_on_stack[0] contains bios submitted by the current ->submit_bio.
+ * bio_list_on_stack[1] contains bios that were submitted before the current
+ * ->submit_bio_bio, but that haven't been processed yet.
+ */
+static blk_qc_t __submit_bio_noacct(struct bio *bio)
+{
+ struct bio_list bio_list_on_stack[2];
+ blk_qc_t ret = BLK_QC_T_NONE;
+
+ BUG_ON(bio->bi_next);
+
+ bio_list_init(&bio_list_on_stack[0]);
+ current->bio_list = bio_list_on_stack;
+
+ do {
+ struct request_queue *q = bio->bi_disk->queue;
+ struct bio_list lower, same;
+
+ if (unlikely(bio_queue_enter(bio) != 0))
+ continue;
+
+ /*
+ * Create a fresh bio_list for all subordinate requests.
+ */
+ bio_list_on_stack[1] = bio_list_on_stack[0];
+ bio_list_init(&bio_list_on_stack[0]);
+
+ ret = do_make_request(bio);
+
+ /*
+ * Sort new bios into those for a lower level and those for the
+ * same level.
+ */
+ bio_list_init(&lower);
+ bio_list_init(&same);
+ while ((bio = bio_list_pop(&bio_list_on_stack[0])) != NULL)
+ if (q == bio->bi_disk->queue)
+ bio_list_add(&same, bio);
+ else
+ bio_list_add(&lower, bio);
+
+ /*
+ * Now assemble so we handle the lowest level first.
+ */
+ bio_list_merge(&bio_list_on_stack[0], &lower);
+ bio_list_merge(&bio_list_on_stack[0], &same);
+ bio_list_merge(&bio_list_on_stack[0], &bio_list_on_stack[1]);
+ } while ((bio = bio_list_pop(&bio_list_on_stack[0])));
+
+ current->bio_list = NULL;
+ return ret;
+}
+
/**
* submit_bio_noacct - re-submit a bio to the block device layer for I/O
* @bio: The bio describing the location in memory and on the device.
@@ -1096,17 +1164,8 @@ static blk_qc_t do_make_request(struct bio *bio)
*/
blk_qc_t submit_bio_noacct(struct bio *bio)
{
- /*
- * bio_list_on_stack[0] contains bios submitted by the current
- * ->submit_bio.
- * bio_list_on_stack[1] contains bios that were submitted before the
- * current ->submit_bio_bio, but that haven't been processed yet.
- */
- struct bio_list bio_list_on_stack[2];
- blk_qc_t ret = BLK_QC_T_NONE;
-
if (!submit_bio_checks(bio))
- goto out;
+ return BLK_QC_T_NONE;

/*
* We only want one ->submit_bio to be active at a time, else
@@ -1120,58 +1179,10 @@ blk_qc_t submit_bio_noacct(struct bio *bio)
*/
if (current->bio_list) {
bio_list_add(&current->bio_list[0], bio);
- goto out;
+ return BLK_QC_T_NONE;
}

- /* following loop may be a bit non-obvious, and so deserves some
- * explanation.
- * Before entering the loop, bio->bi_next is NULL (as all callers
- * ensure that) so we have a list with a single bio.
- * We pretend that we have just taken it off a longer list, so
- * we assign bio_list to a pointer to the bio_list_on_stack,
- * thus initialising the bio_list of new bios to be
- * added. ->submit_bio() may indeed add some more bios
- * through a recursive call to submit_bio_noacct. If it
- * did, we find a non-NULL value in bio_list and re-enter the loop
- * from the top. In this case we really did just take the bio
- * of the top of the list (no pretending) and so remove it from
- * bio_list, and call into ->submit_bio() again.
- */
- BUG_ON(bio->bi_next);
- bio_list_init(&bio_list_on_stack[0]);
- current->bio_list = bio_list_on_stack;
- do {
- struct request_queue *q = bio->bi_disk->queue;
-
- if (likely(bio_queue_enter(bio) == 0)) {
- struct bio_list lower, same;
-
- /* Create a fresh bio_list for all subordinate requests */
- bio_list_on_stack[1] = bio_list_on_stack[0];
- bio_list_init(&bio_list_on_stack[0]);
- ret = do_make_request(bio);
-
- /* sort new bios into those for a lower level
- * and those for the same level
- */
- bio_list_init(&lower);
- bio_list_init(&same);
- while ((bio = bio_list_pop(&bio_list_on_stack[0])) != NULL)
- if (q == bio->bi_disk->queue)
- bio_list_add(&same, bio);
- else
- bio_list_add(&lower, bio);
- /* now assemble so we handle the lowest level first */
- bio_list_merge(&bio_list_on_stack[0], &lower);
- bio_list_merge(&bio_list_on_stack[0], &same);
- bio_list_merge(&bio_list_on_stack[0], &bio_list_on_stack[1]);
- }
- bio = bio_list_pop(&bio_list_on_stack[0]);
- } while (bio);
- current->bio_list = NULL; /* deactivate */
-
-out:
- return ret;
+ return __submit_bio_noacct(bio);
}
EXPORT_SYMBOL(submit_bio_noacct);

--
2.26.2