btrfs: make sure all btrfs_bio::end_io is called in task context

[BACKGROUND]
Btrfs has a lot of different bi_end_io functions, to handle different
raid profiles. But they introduced a lot of different context for
btrfs_bio::end_io() calls:

- Simple read bios
  Run in task context, backed by either endio_meta_workers or
  endio_workers.

- Simple write bios
  Run in irq context.

- RAID56 write or rebuild bios
  Run in task context, backed by rmw_workers.

- Mirrored write bios
  Run in irq context.

This is very inconsistent, and contributes to the huge amount of
workqueues used in btrfs.

[ENHANCEMENT]
Make all above bios to call their btrfs_bio::end_io() in task context,
backed by either endio_meta_workers for metadata, or endio_workers for
data.

For simple write bios, merge the handling into simple_end_io_work().

For mirrored write bios, it will be a little more complex, since both
the original or the cloned bios can run the final btrfs_bio::end_io().

Here we make sure the cloned bios are using btrfs_bioset, to reuse the
end_io_work, and run both original and cloned work inside the workqueue.

And add extra ASSERT()s to make sure btrfs_bio_end_io() is running in
task context.

This not only unifies the context for btrfs_bio::end_io() functions, but
also opens a new door for further btrfs_bio::end_io() related cleanups.

Signed-off-by: Qu Wenruo <wqu@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

Author: adam900710

fs/btrfs/bio.c

@@ -102,6 +102,9 @@ static struct btrfs_bio *btrfs_split_bio(struct btrfs_fs_info *fs_info,
 
 void btrfs_bio_end_io(struct btrfs_bio *bbio, blk_status_t status)
 {
+	/* Make sure we're already in task context. */
+	ASSERT(in_task());
+
 	bbio->bio.bi_status = status;
 	if (bbio->bio.bi_pool == &btrfs_clone_bioset) {
 		struct btrfs_bio *orig_bbio = bbio->private;
@@ -318,15 +321,20 @@ static struct workqueue_struct *btrfs_end_io_wq(const struct btrfs_fs_info *fs_i
 	return fs_info->endio_workers;
 }
 
-static void btrfs_end_bio_work(struct work_struct *work)
+static void simple_end_io_work(struct work_struct *work)
 {
 	struct btrfs_bio *bbio = container_of(work, struct btrfs_bio, end_io_work);
+	struct bio *bio = &bbio->bio;
 
-	/* Metadata reads are checked and repaired by the submitter. */
-	if (is_data_bbio(bbio))
-		btrfs_check_read_bio(bbio, bbio->bio.bi_private);
-	else
-		btrfs_bio_end_io(bbio, bbio->bio.bi_status);
+	if (bio_op(bio) == REQ_OP_READ) {
+		/* Metadata reads are checked and repaired by the submitter. */
+		if (is_data_bbio(bbio))
+			return btrfs_check_read_bio(bbio, bbio->bio.bi_private);
+		return btrfs_bio_end_io(bbio, bbio->bio.bi_status);
+	}
+	if (bio_is_zone_append(bio) && !bio->bi_status)
+		btrfs_record_physical_zoned(bbio);
+	btrfs_bio_end_io(bbio, bbio->bio.bi_status);
 }
 
 static void btrfs_simple_end_io(struct bio *bio)
@@ -340,21 +348,18 @@ static void btrfs_simple_end_io(struct bio *bio)
 	if (bio->bi_status)
 		btrfs_log_dev_io_error(bio, dev);
 
-	if (bio_op(bio) == REQ_OP_READ) {
-		INIT_WORK(&bbio->end_io_work, btrfs_end_bio_work);
-		queue_work(btrfs_end_io_wq(fs_info, bio), &bbio->end_io_work);
-	} else {
-		if (bio_is_zone_append(bio) && !bio->bi_status)
-			btrfs_record_physical_zoned(bbio);
-		btrfs_bio_end_io(bbio, bbio->bio.bi_status);
-	}
+	INIT_WORK(&bbio->end_io_work, simple_end_io_work);
+	queue_work(btrfs_end_io_wq(fs_info, bio), &bbio->end_io_work);
 }
 
 static void btrfs_raid56_end_io(struct bio *bio)
 {
 	struct btrfs_io_context *bioc = bio->bi_private;
 	struct btrfs_bio *bbio = btrfs_bio(bio);
 
+	/* RAID56 endio is always handled in workqueue. */
+	ASSERT(in_task());
+
 	btrfs_bio_counter_dec(bioc->fs_info);
 	bbio->mirror_num = bioc->mirror_num;
 	if (bio_op(bio) == REQ_OP_READ && is_data_bbio(bbio))
@@ -365,11 +370,12 @@ static void btrfs_raid56_end_io(struct bio *bio)
 	btrfs_put_bioc(bioc);
 }
 
-static void btrfs_orig_write_end_io(struct bio *bio)
+static void orig_write_end_io_work(struct work_struct *work)
 {
+	struct btrfs_bio *bbio = container_of(work, struct btrfs_bio, end_io_work);
+	struct bio *bio = &bbio->bio;
 	struct btrfs_io_stripe *stripe = bio->bi_private;
 	struct btrfs_io_context *bioc = stripe->bioc;
-	struct btrfs_bio *bbio = btrfs_bio(bio);
 
 	btrfs_bio_counter_dec(bioc->fs_info);
 
@@ -394,8 +400,18 @@ static void btrfs_orig_write_end_io(struct bio *bio)
 	btrfs_put_bioc(bioc);
 }
 
-static void btrfs_clone_write_end_io(struct bio *bio)
+static void btrfs_orig_write_end_io(struct bio *bio)
+{
+	struct btrfs_bio *bbio = btrfs_bio(bio);
+
+	INIT_WORK(&bbio->end_io_work, orig_write_end_io_work);
+	queue_work(btrfs_end_io_wq(bbio->inode->root->fs_info, bio), &bbio->end_io_work);
+}
+
+static void clone_write_end_io_work(struct work_struct *work)
 {
+	struct btrfs_bio *bbio = container_of(work, struct btrfs_bio, end_io_work);
+	struct bio *bio = &bbio->bio;
 	struct btrfs_io_stripe *stripe = bio->bi_private;
 
 	if (bio->bi_status) {
@@ -410,6 +426,14 @@ static void btrfs_clone_write_end_io(struct bio *bio)
 	bio_put(bio);
 }
 
+static void btrfs_clone_write_end_io(struct bio *bio)
+{
+	struct btrfs_bio *bbio = btrfs_bio(bio);
+
+	INIT_WORK(&bbio->end_io_work, clone_write_end_io_work);
+	queue_work(btrfs_end_io_wq(bbio->inode->root->fs_info, bio), &bbio->end_io_work);
+}
+
 static void btrfs_submit_dev_bio(struct btrfs_device *dev, struct bio *bio)
 {
 	if (!dev || !dev->bdev ||
@@ -456,6 +480,7 @@ static void btrfs_submit_dev_bio(struct btrfs_device *dev, struct bio *bio)
 static void btrfs_submit_mirrored_bio(struct btrfs_io_context *bioc, int dev_nr)
 {
 	struct bio *orig_bio = bioc->orig_bio, *bio;
+	struct btrfs_bio *orig_bbio = btrfs_bio(orig_bio);
 
 	ASSERT(bio_op(orig_bio) != REQ_OP_READ);
 
@@ -464,8 +489,11 @@ static void btrfs_submit_mirrored_bio(struct btrfs_io_context *bioc, int dev_nr)
 		bio = orig_bio;
 		bio->bi_end_io = btrfs_orig_write_end_io;
 	} else {
-		bio = bio_alloc_clone(NULL, orig_bio, GFP_NOFS, &fs_bio_set);
+		/* We need to use endio_work to run end_io in task context. */
+		bio = bio_alloc_clone(NULL, orig_bio, GFP_NOFS, &btrfs_bioset);
 		bio_inc_remaining(orig_bio);
+		btrfs_bio_init(btrfs_bio(bio), orig_bbio->inode,
+			       orig_bbio->file_offset, NULL, NULL);
 		bio->bi_end_io = btrfs_clone_write_end_io;
 	}