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Date: Tue, 26 Nov 2013 16:45:25 -0800
From: Kent Overstreet <kmo@...erainc.com>
To: linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
hch@...radead.org
Cc: Kent Overstreet <kmo@...erainc.com>, Jens Axboe <axboe@...nel.dk>
Subject: [PATCH 22/25] 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@...erainc.com>
Cc: Jens Axboe <axboe@...nel.dk>
---
drivers/md/bcache/io.c | 2 +-
drivers/md/dm-cache-target.c | 6 ++++
drivers/md/dm-snap.c | 1 +
drivers/md/dm-thin.c | 8 +++--
drivers/md/dm-verity.c | 2 +-
fs/bio-integrity.c | 2 +-
fs/bio.c | 76 ++++++++++++++++++++++++++++++++++++++++----
include/linux/bio.h | 2 ++
include/linux/blk_types.h | 2 ++
9 files changed, 90 insertions(+), 11 deletions(-)
diff --git a/drivers/md/bcache/io.c b/drivers/md/bcache/io.c
index 0f0ab65..522f957 100644
--- a/drivers/md/bcache/io.c
+++ b/drivers/md/bcache/io.c
@@ -133,7 +133,7 @@ static void bch_bio_submit_split_done(struct closure *cl)
s->bio->bi_end_io = s->bi_end_io;
s->bio->bi_private = s->bi_private;
- bio_endio(s->bio, 0);
+ bio_endio_nodec(s->bio, 0);
closure_debug_destroy(&s->cl);
mempool_free(s, s->p->bio_split_hook);
diff --git a/drivers/md/dm-cache-target.c b/drivers/md/dm-cache-target.c
index 86f9c83..bf3a206 100644
--- a/drivers/md/dm-cache-target.c
+++ b/drivers/md/dm-cache-target.c
@@ -765,6 +765,12 @@ static void writethrough_endio(struct bio *bio, int err)
dm_unhook_bio(&pb->hook_info, bio);
+ /*
+ * Must bump bi_remaining to allow bio to complete with
+ * restored bi_end_io.
+ */
+ atomic_inc(&bio->bi_remaining);
+
if (err) {
bio_endio(bio, err);
return;
diff --git a/drivers/md/dm-snap.c b/drivers/md/dm-snap.c
index 3ded8c7..80b5cab 100644
--- a/drivers/md/dm-snap.c
+++ b/drivers/md/dm-snap.c
@@ -1415,6 +1415,7 @@ out:
if (full_bio) {
full_bio->bi_end_io = pe->full_bio_end_io;
full_bio->bi_private = pe->full_bio_private;
+ atomic_inc(&full_bio->bi_remaining);
}
free_pending_exception(pe);
diff --git a/drivers/md/dm-thin.c b/drivers/md/dm-thin.c
index a654024..1abb4a2 100644
--- a/drivers/md/dm-thin.c
+++ b/drivers/md/dm-thin.c
@@ -611,8 +611,10 @@ static void cell_defer_no_holder(struct thin_c *tc, struct dm_bio_prison_cell *c
static void process_prepared_mapping_fail(struct dm_thin_new_mapping *m)
{
- if (m->bio)
+ if (m->bio) {
m->bio->bi_end_io = m->saved_bi_end_io;
+ atomic_inc(&m->bio->bi_remaining);
+ }
cell_error(m->tc->pool, m->cell);
list_del(&m->list);
mempool_free(m, m->tc->pool->mapping_pool);
@@ -626,8 +628,10 @@ static void process_prepared_mapping(struct dm_thin_new_mapping *m)
int r;
bio = m->bio;
- if (bio)
+ if (bio) {
bio->bi_end_io = m->saved_bi_end_io;
+ atomic_inc(&bio->bi_remaining);
+ }
if (m->err) {
cell_error(pool, m->cell);
diff --git a/drivers/md/dm-verity.c b/drivers/md/dm-verity.c
index ac35e95..796007a 100644
--- a/drivers/md/dm-verity.c
+++ b/drivers/md/dm-verity.c
@@ -385,7 +385,7 @@ static void verity_finish_io(struct dm_verity_io *io, int error)
bio->bi_end_io = io->orig_bi_end_io;
bio->bi_private = io->orig_bi_private;
- bio_endio(bio, error);
+ bio_endio_nodec(bio, error);
}
static void verity_work(struct work_struct *w)
diff --git a/fs/bio-integrity.c b/fs/bio-integrity.c
index fed744b..9d547d2 100644
--- a/fs/bio-integrity.c
+++ b/fs/bio-integrity.c
@@ -502,7 +502,7 @@ static void bio_integrity_verify_fn(struct work_struct *work)
/* Restore original bio completion handler */
bio->bi_end_io = bip->bip_end_io;
- bio_endio(bio, error);
+ bio_endio_nodec(bio, error);
}
/**
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 @@ void bio_init(struct bio *bio)
{
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 @@ void bio_reset(struct bio *bio)
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 @@ EXPORT_SYMBOL(bio_flush_dcache_pages);
**/
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 (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;
- if (bio->bi_end_io)
- bio->bi_end_io(bio, error);
+ /*
+ * 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)) {
diff --git a/include/linux/bio.h b/include/linux/bio.h
index 0c32a45..64f5169 100644
--- a/include/linux/bio.h
+++ b/include/linux/bio.h
@@ -356,6 +356,7 @@ static inline struct bio *bio_clone_kmalloc(struct bio *bio, gfp_t gfp_mask)
}
extern void bio_endio(struct bio *, int);
+extern void bio_endio_nodec(struct bio *, int);
struct request_queue;
extern int bio_phys_segments(struct request_queue *, struct bio *);
@@ -364,6 +365,7 @@ extern void bio_advance(struct bio *, unsigned);
extern void bio_init(struct bio *);
extern void bio_reset(struct bio *);
+void bio_chain(struct bio *, struct bio *);
extern int bio_add_page(struct bio *, struct page *, unsigned int,unsigned int);
extern int bio_add_pc_page(struct request_queue *, struct bio *, struct page *,
diff --git a/include/linux/blk_types.h b/include/linux/blk_types.h
index d369f8f..bbc3a6c 100644
--- a/include/linux/blk_types.h
+++ b/include/linux/blk_types.h
@@ -65,6 +65,8 @@ struct bio {
unsigned int bi_seg_front_size;
unsigned int bi_seg_back_size;
+ atomic_t bi_remaining;
+
bio_end_io_t *bi_end_io;
void *bi_private;
--
1.8.4.4
--
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