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>

9 files changed, 120 insertions, 72 deletions

diff --git a/fs/btrfs/check-integrity.c b/fs/btrfs/check-integrity.c
index 18af6f48781a..1431a6965017 100644
--- a/fs/btrfs/check-integrity.c
+++ b/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",
diff --git a/fs/btrfs/disk-io.c b/fs/btrfs/disk-io.c
index 4e9ebe1f1827..ca0ea9928210 100644
--- a/fs/btrfs/disk-io.c
+++ b/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;
 
diff --git a/fs/btrfs/extent_io.c b/fs/btrfs/extent_io.c
index d2ac518f90e4..fe1d6c3424a5 100644
--- a/fs/btrfs/extent_io.c
+++ b/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)
 {