On 10/19/2012 04:01 PM, Josef Bacik wrote:
> Alex reported a problem where we were writing between chunks on a rbd
> device. The thing is we do bio_add_page using logical offsets, but the
> physical offset may be different. So when we map the bio now check to see
> if the bio is still ok with the physical offset, and if it is not split the
> bio up and redo the bio_add_page with the physical sector. This fixes the
> problem for Alex and doesn't affect performance in the normal case. Thanks,
>
> Reported-and-tested-by: Alex Elder <elder@xxxxxxxxxxx>
> Signed-off-by: Josef Bacik <jbacik@xxxxxxxxxxxx>
> ---
> fs/btrfs/volumes.c | 159 ++++++++++++++++++++++++++++++++++++++++++---------
> 1 files changed, 131 insertions(+), 28 deletions(-)
>
> diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
> index a8adf26..eaaf0bf 100644
> --- a/fs/btrfs/volumes.c
> +++ b/fs/btrfs/volumes.c
> @@ -4217,6 +4217,113 @@ static noinline void schedule_bio(struct btrfs_root *root,
> &device->work);
> }
>
> +static int bio_size_ok(struct block_device *bdev, struct bio *bio,
> + sector_t sector)
> +{
> + struct bio_vec *prev;
> + struct request_queue *q = bdev_get_queue(bdev);
> + unsigned short max_sectors = queue_max_sectors(q);
> + struct bvec_merge_data bvm = {
> + .bi_bdev = bdev,
> + .bi_sector = sector,
> + .bi_rw = bio->bi_rw,
> + };
> +
> + if (bio->bi_vcnt == 0) {
> + WARN_ON(1);
> + return 1;
> + }
> +
> + prev = &bio->bi_io_vec[bio->bi_vcnt - 1];
> + if ((bio->bi_size >> 9) > max_sectors)
> + return 0;
> +
> + if (!q->merge_bvec_fn)
> + return 1;
> +
> + bvm.bi_size = bio->bi_size - prev->bv_len;
> + if (q->merge_bvec_fn(q, &bvm, prev) < prev->bv_len)
> + return 0;
I wanted to mention one concern that occurred to me over the
weekend.
By checking only the last bio_vec in the bio here it's
conceivable you'll miss another boundary that sits earlier
in the bio.
We technically allow the boundaries of objects that back rbd
disk images to be as small as 4 KB (but by default it's 4 MB).
4 KB is really unlikely, but 256 KB (which is smaller than
128-entry bio) is less of a stretch.
I also came up with a different way of splitting that makes
it moot anyway, obviating the need for doing this check at
all so after a little more testing I'll get that posted.
-Alex
> + return 1;
> +}
> +
> +static void submit_stripe_bio(struct btrfs_root *root, struct btrfs_bio *bbio,
> + struct bio *bio, u64 physical, int dev_nr,
> + int rw, int async)
> +{
> + 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);
> + bio->bi_end_io = btrfs_end_bio;
> + bio->bi_sector = physical >> 9;
> +#ifdef DEBUG
> + {
> + struct rcu_string *name;
> +
> + rcu_read_lock();
> + name = rcu_dereference(dev->name);
> + pr_debug("btrfs_map_bio: rw %d, secor=%llu, dev=%lu "
> + "(%s id %llu), size=%u\n", rw,
> + (u64)bio->bi_sector, (u_long)dev->bdev->bd_dev,
> + name->str, dev->devid, bio->bi_size);
> + rcu_read_unlock();
> + }
> +#endif
> + bio->bi_bdev = dev->bdev;
> + if (async)
> + schedule_bio(root, dev, rw, bio);
> + else
> + btrfsic_submit_bio(rw, bio);
> +}
> +
> +static int breakup_stripe_bio(struct btrfs_root *root, struct btrfs_bio *bbio,
> + struct bio *first_bio, struct btrfs_device *dev,
> + int dev_nr, int rw, int async)
> +{
> + struct bio_vec *bvec = first_bio->bi_io_vec;
> + struct bio *bio;
> + int nr_vecs = bio_get_nr_vecs(dev->bdev);
> + u64 physical = bbio->stripes[dev_nr].physical;
> +
> +again:
> + bio = btrfs_bio_alloc(dev->bdev, physical >> 9, nr_vecs, GFP_NOFS);
> + if (!bio)
> + return -ENOMEM;
> +
> + while (bvec <= (first_bio->bi_io_vec + first_bio->bi_vcnt - 1)) {
> + if (bio_add_page(bio, bvec->bv_page, bvec->bv_len,
> + bvec->bv_offset) < bvec->bv_len) {
> + u64 len = bio->bi_size;
> +
> + atomic_inc(&bbio->stripes_pending);
> + submit_stripe_bio(root, bbio, bio, physical, dev_nr,
> + rw, async);
> + physical += len;
> + goto again;
> + }
> + bvec++;
> + }
> +
> + submit_stripe_bio(root, bbio, bio, physical, dev_nr, rw, async);
> + return 0;
> +}
> +
> +static void bbio_error(struct btrfs_bio *bbio, struct bio *bio, u64 logical)
> +{
> + atomic_inc(&bbio->error);
> + 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;
> + bio->bi_sector = logical >> 9;
> + kfree(bbio);
> + bio_endio(bio, -EIO);
> + }
> +}
> +
> int btrfs_map_bio(struct btrfs_root *root, int rw, struct bio *bio,
> int mirror_num, int async_submit)
> {
> @@ -4255,40 +4362,36 @@ int btrfs_map_bio(struct btrfs_root *root, int rw, struct bio *bio,
> atomic_set(&bbio->stripes_pending, bbio->num_stripes);
>
> while (dev_nr < total_devs) {
> + dev = bbio->stripes[dev_nr].dev;
> + if (!dev || !dev->bdev || (rw & WRITE && !dev->writeable)) {
> + bbio_error(bbio, first_bio, logical);
> + dev_nr++;
> + continue;
> + }
> +
> + /*
> + * Check and see if we're ok with this bio based on it's size
> + * and offset with the given device.
> + */
> + if (!bio_size_ok(dev->bdev, first_bio,
> + bbio->stripes[dev_nr].physical >> 9)) {
> + ret = breakup_stripe_bio(root, bbio, first_bio, dev,
> + dev_nr, rw, async_submit);
> + BUG_ON(ret);
> + dev_nr++;
> + continue;
> + }
> +
> if (dev_nr < total_devs - 1) {
> bio = bio_clone(first_bio, GFP_NOFS);
> BUG_ON(!bio); /* -ENOMEM */
> } else {
> bio = first_bio;
> }
> - bio->bi_private = bbio;
> - bio->bi_private = merge_stripe_index_into_bio_private(
> - bio->bi_private, (unsigned int)dev_nr);
> - bio->bi_end_io = btrfs_end_bio;
> - bio->bi_sector = bbio->stripes[dev_nr].physical >> 9;
> - dev = bbio->stripes[dev_nr].dev;
> - if (dev && dev->bdev && (rw != WRITE || dev->writeable)) {
> -#ifdef DEBUG
> - struct rcu_string *name;
> -
> - rcu_read_lock();
> - name = rcu_dereference(dev->name);
> - pr_debug("btrfs_map_bio: rw %d, secor=%llu, dev=%lu "
> - "(%s id %llu), size=%u\n", rw,
> - (u64)bio->bi_sector, (u_long)dev->bdev->bd_dev,
> - name->str, dev->devid, bio->bi_size);
> - rcu_read_unlock();
> -#endif
> - bio->bi_bdev = dev->bdev;
> - if (async_submit)
> - schedule_bio(root, dev, rw, bio);
> - else
> - btrfsic_submit_bio(rw, bio);
> - } else {
> - bio->bi_bdev = root->fs_info->fs_devices->latest_bdev;
> - bio->bi_sector = logical >> 9;
> - bio_endio(bio, -EIO);
> - }
> +
> + submit_stripe_bio(root, bbio, bio,
> + bbio->stripes[dev_nr].physical, dev_nr, rw,
> + async_submit);
> dev_nr++;
> }
> return 0;
>
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