Btrfs: use a btrfs bioset instead of abusing bio internals

Btrfs has been pointer tagging bi_private and using bi_bdev
to store the stripe index and mirror number of failed IOs.

As bios bubble back up through the call chain, we use these
to decide if and how to retry our IOs.  They are also used
to count IO failures on a per device basis.

Recently a bio tracepoint was added lead to crashes because
we were abusing bi_bdev.

This commit adds a btrfs bioset, and creates explicit fields
for the mirror number and stripe index.  The plan is to
extend this structure for all of the fields currently in
struct btrfs_bio, which will mean one less kmalloc in
our IO path.

Signed-off-by: Chris Mason <chris.mason@fusionio.com>
Reported-by: Tejun Heo <tj@kernel.org>

1 files changed, 43 insertions, 21 deletions

diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
index 1669c3b..d59dddf 100644
--- a/fs/btrfs/inode.c
+++ b/fs/btrfs/inode.c
@@ -6927,7 +6927,11 @@ struct btrfs_dio_private {
 	/* IO errors */
 	int errors;
 
+	/* orig_bio is our btrfs_io_bio */
 	struct bio *orig_bio;
+
+	/* dio_bio came from fs/direct-io.c */
+	struct bio *dio_bio;
 };
 
 static void btrfs_endio_direct_read(struct bio *bio, int err)
@@ -6937,6 +6941,7 @@ static void btrfs_endio_direct_read(struct bio *bio, int err)
 	struct bio_vec *bvec = bio->bi_io_vec;
 	struct inode *inode = dip->inode;
 	struct btrfs_root *root = BTRFS_I(inode)->root;
+	struct bio *dio_bio;
 	u64 start;
 
 	start = dip->logical_offset;
@@ -6976,14 +6981,15 @@ failed:
 
 	unlock_extent(&BTRFS_I(inode)->io_tree, dip->logical_offset,
 		      dip->logical_offset + dip->bytes - 1);
-	bio->bi_private = dip->private;
+	dio_bio = dip->dio_bio;
 
 	kfree(dip);
 
 	/* If we had a csum failure make sure to clear the uptodate flag */
 	if (err)
-		clear_bit(BIO_UPTODATE, &bio->bi_flags);
-	dio_end_io(bio, err);
+		clear_bit(BIO_UPTODATE, &dio_bio->bi_flags);
+	dio_end_io(dio_bio, err);
+	bio_put(bio);
 }
 
 static void btrfs_endio_direct_write(struct bio *bio, int err)
@@ -6994,6 +7000,7 @@ static void btrfs_endio_direct_write(struct bio *bio, int err)
 	struct btrfs_ordered_extent *ordered = NULL;
 	u64 ordered_offset = dip->logical_offset;
 	u64 ordered_bytes = dip->bytes;
+	struct bio *dio_bio;
 	int ret;
 
 	if (err)
@@ -7021,14 +7028,15 @@ out_test:
 		goto again;
 	}
 out_done:
-	bio->bi_private = dip->private;
+	dio_bio = dip->dio_bio;
 
 	kfree(dip);
 
 	/* If we had an error make sure to clear the uptodate flag */
 	if (err)
-		clear_bit(BIO_UPTODATE, &bio->bi_flags);
-	dio_end_io(bio, err);
+		clear_bit(BIO_UPTODATE, &dio_bio->bi_flags);
+	dio_end_io(dio_bio, err);
+	bio_put(bio);
 }
 
 static int __btrfs_submit_bio_start_direct_io(struct inode *inode, int rw,
@@ -7064,10 +7072,10 @@ static void btrfs_end_dio_bio(struct bio *bio, int err)
 	if (!atomic_dec_and_test(&dip->pending_bios))
 		goto out;
 
-	if (dip->errors)
+	if (dip->errors) {
 		bio_io_error(dip->orig_bio);
-	else {
-		set_bit(BIO_UPTODATE, &dip->orig_bio->bi_flags);
+	} else {
+		set_bit(BIO_UPTODATE, &dip->dio_bio->bi_flags);
 		bio_endio(dip->orig_bio, 0);
 	}
 out:
@@ -7242,25 +7250,34 @@ out_err:
 	return 0;
 }
 
-static void btrfs_submit_direct(int rw, struct bio *bio, struct inode *inode,
-				loff_t file_offset)
+static void btrfs_submit_direct(int rw, struct bio *dio_bio,
+				struct inode *inode, loff_t file_offset)
 {
 	struct btrfs_root *root = BTRFS_I(inode)->root;
 	struct btrfs_dio_private *dip;
-	struct bio_vec *bvec = bio->bi_io_vec;
+	struct bio_vec *bvec = dio_bio->bi_io_vec;
+	struct bio *io_bio;
 	int skip_sum;
 	int write = rw & REQ_WRITE;
 	int ret = 0;
 
 	skip_sum = BTRFS_I(inode)->flags & BTRFS_INODE_NODATASUM;
 
+	io_bio = btrfs_bio_clone(dio_bio, GFP_NOFS);
+
+	if (!io_bio) {
+		ret = -ENOMEM;
+		goto free_ordered;
+	}
+
 	dip = kmalloc(sizeof(*dip), GFP_NOFS);
 	if (!dip) {
 		ret = -ENOMEM;
-		goto free_ordered;
+		goto free_io_bio;
 	}
 
-	dip->private = bio->bi_private;
+	dip->private = dio_bio->bi_private;
+	io_bio->bi_private = dio_bio->bi_private;
 	dip->inode = inode;
 	dip->logical_offset = file_offset;
 
@@ -7268,22 +7285,27 @@ static void btrfs_submit_direct(int rw, struct bio *bio, struct inode *inode,
 	do {
 		dip->bytes += bvec->bv_len;
 		bvec++;
-	} while (bvec <= (bio->bi_io_vec + bio->bi_vcnt - 1));
+	} while (bvec <= (dio_bio->bi_io_vec + dio_bio->bi_vcnt - 1));
 
-	dip->disk_bytenr = (u64)bio->bi_sector << 9;
-	bio->bi_private = dip;
+	dip->disk_bytenr = (u64)dio_bio->bi_sector << 9;
+	io_bio->bi_private = dip;
 	dip->errors = 0;
-	dip->orig_bio = bio;
+	dip->orig_bio = io_bio;
+	dip->dio_bio = dio_bio;
 	atomic_set(&dip->pending_bios, 0);
 
 	if (write)
-		bio->bi_end_io = btrfs_endio_direct_write;
+		io_bio->bi_end_io = btrfs_endio_direct_write;
 	else
-		bio->bi_end_io = btrfs_endio_direct_read;
+		io_bio->bi_end_io = btrfs_endio_direct_read;
 
 	ret = btrfs_submit_direct_hook(rw, dip, skip_sum);
 	if (!ret)
 		return;
+
+free_io_bio:
+	bio_put(io_bio);
+
 free_ordered:
 	/*
 	 * If this is a write, we need to clean up the reserved space and kill
@@ -7299,7 +7321,7 @@ free_ordered:
 		btrfs_put_ordered_extent(ordered);
 		btrfs_put_ordered_extent(ordered);
 	}
-	bio_endio(bio, ret);
+	bio_endio(dio_bio, ret);
 }
 
 static ssize_t check_direct_IO(struct btrfs_root *root, int rw, struct kiocb *iocb,