block: Generic bio chaining
This adds a generic mechanism for chaining bio completions. This is
going to be used for a bio_split() replacement, and it turns out to be
very useful in a fair amount of driver code - a fair number of drivers
were implementing this in their own roundabout ways, often painfully.
Note that this means it's no longer to call bio_endio() more than once
on the same bio! This can cause problems for drivers that save/restore
bi_end_io. Arguably they shouldn't be saving/restoring bi_end_io at all
- in all but the simplest cases they'd be better off just cloning the
bio, and immutable biovecs is making bio cloning cheaper. But for now,
we add a bio_endio_nodec() for these cases.
Signed-off-by: Kent Overstreet <kmo@daterainc.com>
Cc: Jens Axboe <axboe@kernel.dk>
diff --git a/fs/bio.c b/fs/bio.c
index e6dfa06..b0a16db 100644
--- a/fs/bio.c
+++ b/fs/bio.c
@@ -273,6 +273,7 @@
{
memset(bio, 0, sizeof(*bio));
bio->bi_flags = 1 << BIO_UPTODATE;
+ atomic_set(&bio->bi_remaining, 1);
atomic_set(&bio->bi_cnt, 1);
}
EXPORT_SYMBOL(bio_init);
@@ -295,9 +296,35 @@
memset(bio, 0, BIO_RESET_BYTES);
bio->bi_flags = flags|(1 << BIO_UPTODATE);
+ atomic_set(&bio->bi_remaining, 1);
}
EXPORT_SYMBOL(bio_reset);
+static void bio_chain_endio(struct bio *bio, int error)
+{
+ bio_endio(bio->bi_private, error);
+ bio_put(bio);
+}
+
+/**
+ * bio_chain - chain bio completions
+ *
+ * The caller won't have a bi_end_io called when @bio completes - instead,
+ * @parent's bi_end_io won't be called until both @parent and @bio have
+ * completed; the chained bio will also be freed when it completes.
+ *
+ * The caller must not set bi_private or bi_end_io in @bio.
+ */
+void bio_chain(struct bio *bio, struct bio *parent)
+{
+ BUG_ON(bio->bi_private || bio->bi_end_io);
+
+ bio->bi_private = parent;
+ bio->bi_end_io = bio_chain_endio;
+ atomic_inc(&parent->bi_remaining);
+}
+EXPORT_SYMBOL(bio_chain);
+
static void bio_alloc_rescue(struct work_struct *work)
{
struct bio_set *bs = container_of(work, struct bio_set, rescue_work);
@@ -1719,16 +1746,53 @@
**/
void bio_endio(struct bio *bio, int error)
{
- if (error)
- clear_bit(BIO_UPTODATE, &bio->bi_flags);
- else if (!test_bit(BIO_UPTODATE, &bio->bi_flags))
- error = -EIO;
+ while (bio) {
+ BUG_ON(atomic_read(&bio->bi_remaining) <= 0);
- if (bio->bi_end_io)
- bio->bi_end_io(bio, error);
+ if (error)
+ clear_bit(BIO_UPTODATE, &bio->bi_flags);
+ else if (!test_bit(BIO_UPTODATE, &bio->bi_flags))
+ error = -EIO;
+
+ if (!atomic_dec_and_test(&bio->bi_remaining))
+ return;
+
+ /*
+ * Need to have a real endio function for chained bios,
+ * otherwise various corner cases will break (like stacking
+ * block devices that save/restore bi_end_io) - however, we want
+ * to avoid unbounded recursion and blowing the stack. Tail call
+ * optimization would handle this, but compiling with frame
+ * pointers also disables gcc's sibling call optimization.
+ */
+ if (bio->bi_end_io == bio_chain_endio) {
+ struct bio *parent = bio->bi_private;
+ bio_put(bio);
+ bio = parent;
+ } else {
+ if (bio->bi_end_io)
+ bio->bi_end_io(bio, error);
+ bio = NULL;
+ }
+ }
}
EXPORT_SYMBOL(bio_endio);
+/**
+ * bio_endio_nodec - end I/O on a bio, without decrementing bi_remaining
+ * @bio: bio
+ * @error: error, if any
+ *
+ * For code that has saved and restored bi_end_io; thing hard before using this
+ * function, probably you should've cloned the entire bio.
+ **/
+void bio_endio_nodec(struct bio *bio, int error)
+{
+ atomic_inc(&bio->bi_remaining);
+ bio_endio(bio, error);
+}
+EXPORT_SYMBOL(bio_endio_nodec);
+
void bio_pair_release(struct bio_pair *bp)
{
if (atomic_dec_and_test(&bp->cnt)) {