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, 6 insertions, 35 deletions

diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
index a191bac..317afc7 100644
--- a/fs/btrfs/volumes.c
+++ b/fs/btrfs/volumes.c
@@ -5019,42 +5019,16 @@ int btrfs_rmap_block(struct btrfs_mapping_tree *map_tree,
 	return 0;
 }
 
-static void *merge_stripe_index_into_bio_private(void *bi_private,
-						 unsigned int stripe_index)
-{
-	/*
-	 * with single, dup, RAID0, RAID1 and RAID10, stripe_index is
-	 * at most 1.
-	 * The alternative solution (instead of stealing bits from the
-	 * pointer) would be to allocate an intermediate structure
-	 * that contains the old private pointer plus the stripe_index.
-	 */
-	BUG_ON((((uintptr_t)bi_private) & 3) != 0);
-	BUG_ON(stripe_index > 3);
-	return (void *)(((uintptr_t)bi_private) | stripe_index);
-}
-
-static struct btrfs_bio *extract_bbio_from_bio_private(void *bi_private)
-{
-	return (struct btrfs_bio *)(((uintptr_t)bi_private) & ~((uintptr_t)3));
-}
-
-static unsigned int extract_stripe_index_from_bio_private(void *bi_private)
-{
-	return (unsigned int)((uintptr_t)bi_private) & 3;
-}
-
 static void btrfs_end_bio(struct bio *bio, int err)
 {
-	struct btrfs_bio *bbio = extract_bbio_from_bio_private(bio->bi_private);
+	struct btrfs_bio *bbio = bio->bi_private;
 	int is_orig_bio = 0;
 
 	if (err) {
 		atomic_inc(&bbio->error);
 		if (err == -EIO || err == -EREMOTEIO) {
 			unsigned int stripe_index =
-				extract_stripe_index_from_bio_private(
-					bio->bi_private);
+				btrfs_io_bio(bio)->stripe_index;
 			struct btrfs_device *dev;
 
 			BUG_ON(stripe_index >= bbio->num_stripes);
@@ -5084,8 +5058,7 @@ static void btrfs_end_bio(struct bio *bio, int err)
 		}
 		bio->bi_private = bbio->private;
 		bio->bi_end_io = bbio->end_io;
-		bio->bi_bdev = (struct block_device *)
-					(unsigned long)bbio->mirror_num;
+		btrfs_io_bio(bio)->mirror_num = bbio->mirror_num;
 		/* only send an error to the higher layers if it is
 		 * beyond the tolerance of the btrfs bio
 		 */
@@ -5211,8 +5184,7 @@ static void submit_stripe_bio(struct btrfs_root *root, struct btrfs_bio *bbio,
 	struct btrfs_device *dev = bbio->stripes[dev_nr].dev;
 
 	bio->bi_private = bbio;
-	bio->bi_private = merge_stripe_index_into_bio_private(
-			bio->bi_private, (unsigned int)dev_nr);
+	btrfs_io_bio(bio)->stripe_index = dev_nr;
 	bio->bi_end_io = btrfs_end_bio;
 	bio->bi_sector = physical >> 9;
 #ifdef DEBUG
@@ -5273,8 +5245,7 @@ static void bbio_error(struct btrfs_bio *bbio, struct bio *bio, u64 logical)
 	if (atomic_dec_and_test(&bbio->stripes_pending)) {
 		bio->bi_private = bbio->private;
 		bio->bi_end_io = bbio->end_io;
-		bio->bi_bdev = (struct block_device *)
-			(unsigned long)bbio->mirror_num;
+		btrfs_io_bio(bio)->mirror_num = bbio->mirror_num;
 		bio->bi_sector = logical >> 9;
 		kfree(bbio);
 		bio_endio(bio, -EIO);
@@ -5352,7 +5323,7 @@ int btrfs_map_bio(struct btrfs_root *root, int rw, struct bio *bio,
 		}
 
 		if (dev_nr < total_devs - 1) {
-			bio = bio_clone(first_bio, GFP_NOFS);
+			bio = btrfs_bio_clone(first_bio, GFP_NOFS);
 			BUG_ON(!bio); /* -ENOMEM */
 		} else {
 			bio = first_bio;