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>

fs/btrfs/check-integrity.c

@@ -1700,7 +1700,7 @@ static int btrfsic_read_block(struct btrfsic_state *state,
 		unsigned int j;
 		DECLARE_COMPLETION_ONSTACK(complete);
 
-		bio = bio_alloc(GFP_NOFS, num_pages - i);
+		bio = btrfs_io_bio_alloc(GFP_NOFS, num_pages - i);
 		if (!bio) {
 			printk(KERN_INFO
 			       "btrfsic: bio_alloc() for %u pages failed!\n",

fs/btrfs/disk-io.c

@@ -3128,7 +3128,7 @@ static int write_dev_flush(struct btrfs_device *device, int wait)
 	 * caller
 	 */
 	device->flush_bio = NULL;
-	bio = bio_alloc(GFP_NOFS, 0);
+	bio = btrfs_io_bio_alloc(GFP_NOFS, 0);
 	if (!bio)
 		return -ENOMEM;
 

fs/btrfs/extent_io.c

@@ -23,6 +23,7 @@
 
 static struct kmem_cache *extent_state_cache;
 static struct kmem_cache *extent_buffer_cache;
+static struct bio_set *btrfs_bioset;
 
 #ifdef CONFIG_BTRFS_DEBUG
 static LIST_HEAD(buffers);
@@ -125,10 +126,20 @@ int __init extent_io_init(void)
 			SLAB_RECLAIM_ACCOUNT | SLAB_MEM_SPREAD, NULL);
 	if (!extent_buffer_cache)
 		goto free_state_cache;
+
+	btrfs_bioset = bioset_create(BIO_POOL_SIZE,
+				     offsetof(struct btrfs_io_bio, bio));
+	if (!btrfs_bioset)
+		goto free_buffer_cache;
 	return 0;
 
+free_buffer_cache:
+	kmem_cache_destroy(extent_buffer_cache);
+	extent_buffer_cache = NULL;
+
 free_state_cache:
 	kmem_cache_destroy(extent_state_cache);
+	extent_state_cache = NULL;
 	return -ENOMEM;
 }
 
@@ -145,6 +156,8 @@ void extent_io_exit(void)
 		kmem_cache_destroy(extent_state_cache);
 	if (extent_buffer_cache)
 		kmem_cache_destroy(extent_buffer_cache);
+	if (btrfs_bioset)
+		bioset_free(btrfs_bioset);
 }
 
 void extent_io_tree_init(struct extent_io_tree *tree,
@@ -2046,7 +2059,7 @@ int repair_io_failure(struct btrfs_fs_info *fs_info, u64 start,
 	if (btrfs_is_parity_mirror(map_tree, logical, length, mirror_num))
 		return 0;
 
-	bio = bio_alloc(GFP_NOFS, 1);
+	bio = btrfs_io_bio_alloc(GFP_NOFS, 1);
 	if (!bio)
 		return -EIO;
 	bio->bi_private = &compl;
@@ -2336,7 +2349,7 @@ static int bio_readpage_error(struct bio *failed_bio, struct page *page,
 		return -EIO;
 	}
 
-	bio = bio_alloc(GFP_NOFS, 1);
+	bio = btrfs_io_bio_alloc(GFP_NOFS, 1);
 	if (!bio) {
 		free_io_failure(inode, failrec, 0);
 		return -EIO;
@@ -2457,10 +2470,11 @@ static void end_bio_extent_readpage(struct bio *bio, int err)
 		struct page *page = bvec->bv_page;
 		struct extent_state *cached = NULL;
 		struct extent_state *state;
+		struct btrfs_io_bio *io_bio = btrfs_io_bio(bio);
 
 		pr_debug("end_bio_extent_readpage: bi_sector=%llu, err=%d, "
-			 "mirror=%ld\n", (u64)bio->bi_sector, err,
-			 (long int)bio->bi_bdev);
+			 "mirror=%lu\n", (u64)bio->bi_sector, err,
+			 io_bio->mirror_num);
 		tree = &BTRFS_I(page->mapping->host)->io_tree;
 
 		start = page_offset(page) + bvec->bv_offset;
@@ -2485,7 +2499,7 @@ static void end_bio_extent_readpage(struct bio *bio, int err)
 		}
 		spin_unlock(&tree->lock);
 
-		mirror = (int)(unsigned long)bio->bi_bdev;
+		mirror = io_bio->mirror_num;
 		if (uptodate && tree->ops && tree->ops->readpage_end_io_hook) {
 			ret = tree->ops->readpage_end_io_hook(page, start, end,
 							      state, mirror);
@@ -2550,17 +2564,23 @@ static void end_bio_extent_readpage(struct bio *bio, int err)
 	bio_put(bio);
 }
 
+/*
+ * this allocates from the btrfs_bioset.  We're returning a bio right now
+ * but you can call btrfs_io_bio for the appropriate container_of magic
+ */
 struct bio *
 btrfs_bio_alloc(struct block_device *bdev, u64 first_sector, int nr_vecs,
 		gfp_t gfp_flags)
 {
 	struct bio *bio;
 
-	bio = bio_alloc(gfp_flags, nr_vecs);
+	bio = bio_alloc_bioset(gfp_flags, nr_vecs, btrfs_bioset);
 
 	if (bio == NULL && (current->flags & PF_MEMALLOC)) {
-		while (!bio && (nr_vecs /= 2))
-			bio = bio_alloc(gfp_flags, nr_vecs);
+		while (!bio && (nr_vecs /= 2)) {
+			bio = bio_alloc_bioset(gfp_flags,
+					       nr_vecs, btrfs_bioset);
+		}
 	}
 
 	if (bio) {
@@ -2571,6 +2591,19 @@ btrfs_bio_alloc(struct block_device *bdev, u64 first_sector, int nr_vecs,
 	return bio;
 }
 
+struct bio *btrfs_bio_clone(struct bio *bio, gfp_t gfp_mask)
+{
+	return bio_clone_bioset(bio, gfp_mask, btrfs_bioset);
+}
+
+
+/* this also allocates from the btrfs_bioset */
+struct bio *btrfs_io_bio_alloc(gfp_t gfp_mask, unsigned int nr_iovecs)
+{
+	return bio_alloc_bioset(gfp_mask, nr_iovecs, btrfs_bioset);
+}
+
+
 static int __must_check submit_one_bio(int rw, struct bio *bio,
 				       int mirror_num, unsigned long bio_flags)
 {

fs/btrfs/extent_io.h

@@ -336,6 +336,8 @@ int extent_clear_unlock_delalloc(struct inode *inode,
 struct bio *
 btrfs_bio_alloc(struct block_device *bdev, u64 first_sector, int nr_vecs,
 		gfp_t gfp_flags);
+struct bio *btrfs_io_bio_alloc(gfp_t gfp_mask, unsigned int nr_iovecs);
+struct bio *btrfs_bio_clone(struct bio *bio, gfp_t gfp_mask);
 
 struct btrfs_fs_info;
 

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,

fs/btrfs/raid56.c

@@ -1050,7 +1050,7 @@ static int rbio_add_io_page(struct btrfs_raid_bio *rbio,
 	}
 
 	/* put a new bio on the list */
-	bio = bio_alloc(GFP_NOFS, bio_max_len >> PAGE_SHIFT?:1);
+	bio = btrfs_io_bio_alloc(GFP_NOFS, bio_max_len >> PAGE_SHIFT?:1);
 	if (!bio)
 		return -ENOMEM;
 

fs/btrfs/scrub.c

@@ -1296,7 +1296,7 @@ static void scrub_recheck_block(struct btrfs_fs_info *fs_info,
 		}
 
 		WARN_ON(!page->page);
-		bio = bio_alloc(GFP_NOFS, 1);
+		bio = btrfs_io_bio_alloc(GFP_NOFS, 1);
 		if (!bio) {
 			page->io_error = 1;
 			sblock->no_io_error_seen = 0;
@@ -1431,7 +1431,7 @@ static int scrub_repair_page_from_good_copy(struct scrub_block *sblock_bad,
 			return -EIO;
 		}
 
-		bio = bio_alloc(GFP_NOFS, 1);
+		bio = btrfs_io_bio_alloc(GFP_NOFS, 1);
 		if (!bio)
 			return -EIO;
 		bio->bi_bdev = page_bad->dev->bdev;
@@ -1522,7 +1522,7 @@ again:
 		sbio->dev = wr_ctx->tgtdev;
 		bio = sbio->bio;
 		if (!bio) {
-			bio = bio_alloc(GFP_NOFS, wr_ctx->pages_per_wr_bio);
+			bio = btrfs_io_bio_alloc(GFP_NOFS, wr_ctx->pages_per_wr_bio);
 			if (!bio) {
 				mutex_unlock(&wr_ctx->wr_lock);
 				return -ENOMEM;
@@ -1930,7 +1930,7 @@ again:
 		sbio->dev = spage->dev;
 		bio = sbio->bio;
 		if (!bio) {
-			bio = bio_alloc(GFP_NOFS, sctx->pages_per_rd_bio);
+			bio = btrfs_io_bio_alloc(GFP_NOFS, sctx->pages_per_rd_bio);
 			if (!bio)
 				return -ENOMEM;
 			sbio->bio = bio;
@@ -3307,7 +3307,7 @@ static int write_page_nocow(struct scrub_ctx *sctx,
 			"btrfs: scrub write_page_nocow(bdev == NULL) is unexpected!\n");
 		return -EIO;
 	}
-	bio = bio_alloc(GFP_NOFS, 1);
+	bio = btrfs_io_bio_alloc(GFP_NOFS, 1);
 	if (!bio) {
 		spin_lock(&sctx->stat_lock);
 		sctx->stat.malloc_errors++;

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;

fs/btrfs/volumes.h

@@ -152,6 +152,26 @@ struct btrfs_fs_devices {
 	int rotating;
 };
 
+/*
+ * we need the mirror number and stripe index to be passed around
+ * the call chain while we are processing end_io (especially errors).
+ * Really, what we need is a btrfs_bio structure that has this info
+ * and is properly sized with its stripe array, but we're not there
+ * quite yet.  We have our own btrfs bioset, and all of the bios
+ * we allocate are actually btrfs_io_bios.  We'll cram as much of
+ * struct btrfs_bio as we can into this over time.
+ */
+struct btrfs_io_bio {
+	unsigned long mirror_num;
+	unsigned long stripe_index;
+	struct bio bio;
+};
+
+static inline struct btrfs_io_bio *btrfs_io_bio(struct bio *bio)
+{
+	return container_of(bio, struct btrfs_io_bio, bio);
+}
+
 struct btrfs_bio_stripe {
 	struct btrfs_device *dev;
 	u64 physical;