On Mon, Feb 05, 2018 at 04:15:02PM -0700, Liu Bo wrote:
> Btrfs tries its best to tolerate write errors, but kind of silently
> (except some messages in kernel log).
>
> For raid1 and raid10, this is usually not a problem because there is a
> copy as backup, while for parity based raid setup, i.e. raid5 and
> raid6, the problem is that, if a write error occurs due to some bad
> sectors, one horizonal stripe becomes degraded and the number of write
> errors it can tolerate gets reduced by one, now if two disk fails,
> data may be lost forever.
>
> One way to mitigate the data loss pain is to expose 'bad chunks',
> i.e. degraded chunks, to users, so that they can use 'btrfs balance'
> to relocate the whole chunk and get the full raid6 protection again
> (if the relocation works).
>
> This introduces 'bad_chunks' in btrfs's per-fs sysfs directory. Once
> a chunk of raid5 or raid6 becomes degraded, it will appear in
> 'bad_chunks'.
>
> Signed-off-by: Liu Bo <bo.li....@oracle.com>
> ---
> - In this patch, 'bad chunks' is not persistent on disk, but it can be
> added if it's thought to be a good idea.
> - This is lightly tested, comments are very welcome.
Hmmm... sorry to be late to the party and dump a bunch of semirelated
work suggestions, but what if you implemented GETFSMAP for btrfs? Then
you could define a new 'defective' fsmap type/flag/whatever and export
it for whatever metadata/filedata/whatever is now screwed up? Existing
interface, you don't have to kludge sysfs data, none of this string
interpretation stuff...
--D
>
> fs/btrfs/ctree.h | 8 +++++++
> fs/btrfs/disk-io.c | 2 ++
> fs/btrfs/extent-tree.c | 13 +++++++++++
> fs/btrfs/raid56.c | 59
> ++++++++++++++++++++++++++++++++++++++++++++++++--
> fs/btrfs/sysfs.c | 26 ++++++++++++++++++++++
> fs/btrfs/volumes.c | 15 +++++++++++--
> fs/btrfs/volumes.h | 2 ++
> 7 files changed, 121 insertions(+), 4 deletions(-)
>
> diff --git a/fs/btrfs/ctree.h b/fs/btrfs/ctree.h
> index 13c260b..08aad65 100644
> --- a/fs/btrfs/ctree.h
> +++ b/fs/btrfs/ctree.h
> @@ -1101,6 +1101,9 @@ struct btrfs_fs_info {
> spinlock_t ref_verify_lock;
> struct rb_root block_tree;
> #endif
> +
> + struct list_head bad_chunks;
> + seqlock_t bc_lock;
> };
>
> static inline struct btrfs_fs_info *btrfs_sb(struct super_block *sb)
> @@ -2568,6 +2571,11 @@ static inline gfp_t btrfs_alloc_write_mask(struct
> address_space *mapping)
>
> /* extent-tree.c */
>
> +struct btrfs_bad_chunk {
> + u64 chunk_offset;
> + struct list_head list;
> +};
> +
> enum btrfs_inline_ref_type {
> BTRFS_REF_TYPE_INVALID = 0,
> BTRFS_REF_TYPE_BLOCK = 1,
> diff --git a/fs/btrfs/disk-io.c b/fs/btrfs/disk-io.c
> index a8ecccf..061e7f94 100644
> --- a/fs/btrfs/disk-io.c
> +++ b/fs/btrfs/disk-io.c
> @@ -2568,6 +2568,8 @@ int open_ctree(struct super_block *sb,
> init_waitqueue_head(&fs_info->async_submit_wait);
>
> INIT_LIST_HEAD(&fs_info->pinned_chunks);
> + INIT_LIST_HEAD(&fs_info->bad_chunks);
> + seqlock_init(&fs_info->bc_lock);
>
> /* Usable values until the real ones are cached from the superblock */
> fs_info->nodesize = 4096;
> diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c
> index 2f43285..3ca7cb4 100644
> --- a/fs/btrfs/extent-tree.c
> +++ b/fs/btrfs/extent-tree.c
> @@ -9903,6 +9903,19 @@ int btrfs_free_block_groups(struct btrfs_fs_info *info)
> kobject_del(&space_info->kobj);
> kobject_put(&space_info->kobj);
> }
> +
> + /* Clean up bad chunks. */
> + write_seqlock_irq(&info->bc_lock);
> + while (!list_empty(&info->bad_chunks)) {
> + struct btrfs_bad_chunk *bc;
> +
> + bc = list_first_entry(&info->bad_chunks,
> + struct btrfs_bad_chunk, list);
> + list_del_init(&bc->list);
> + kfree(bc);
> + }
> + write_sequnlock_irq(&info->bc_lock);
> +
> return 0;
> }
>
> diff --git a/fs/btrfs/raid56.c b/fs/btrfs/raid56.c
> index a7f7925..e960247 100644
> --- a/fs/btrfs/raid56.c
> +++ b/fs/btrfs/raid56.c
> @@ -888,14 +888,19 @@ static void rbio_orig_end_io(struct btrfs_raid_bio
> *rbio, blk_status_t err)
> }
>
> /*
> - * end io function used by finish_rmw. When we finally
> - * get here, we've written a full stripe
> + * end io function used by finish_rmw. When we finally get here, we've
> written
> + * a full stripe.
> + *
> + * Note that this is not under interrupt context as we queued endio to
> workers.
> */
> static void raid_write_end_io(struct bio *bio)
> {
> struct btrfs_raid_bio *rbio = bio->bi_private;
> blk_status_t err = bio->bi_status;
> int max_errors;
> + u64 stripe_start = rbio->bbio->raid_map[0];
> + struct btrfs_fs_info *fs_info = rbio->fs_info;
> + int err_cnt;
>
> if (err)
> fail_bio_stripe(rbio, bio);
> @@ -908,12 +913,58 @@ static void raid_write_end_io(struct bio *bio)
> err = BLK_STS_OK;
>
> /* OK, we have read all the stripes we need to. */
> + err_cnt = atomic_read(&rbio->error);
> max_errors = (rbio->operation == BTRFS_RBIO_PARITY_SCRUB) ?
> 0 : rbio->bbio->max_errors;
> if (atomic_read(&rbio->error) > max_errors)
> err = BLK_STS_IOERR;
>
> rbio_orig_end_io(rbio, err);
> +
> + /*
> + * If there is any error, this stripe is a degraded one, so is the whole
> + * chunk, expose this chunk info to sysfs.
> + */
> + if (unlikely(err_cnt)) {
> + struct btrfs_bad_chunk *bc;
> + struct btrfs_bad_chunk *tmp;
> + struct extent_map *em;
> + unsigned long flags;
> +
> + em = get_chunk_map(fs_info, stripe_start, 1);
> + if (IS_ERR(em))
> + return;
> +
> + bc = kzalloc(sizeof(*bc), GFP_NOFS);
> + /* If allocation fails, it's OK. */
> + if (!bc) {
> + free_extent_map(em);
> + return;
> + }
> +
> + write_seqlock_irqsave(&fs_info->bc_lock, flags);
> + list_for_each_entry(tmp, &fs_info->bad_chunks, list) {
> + if (tmp->chunk_offset != em->start)
> + continue;
> +
> + /*
> + * Don't bother if this chunk has already been recorded.
> + */
> + write_sequnlock_irqrestore(&fs_info->bc_lock, flags);
> + kfree(bc);
> + free_extent_map(em);
> + return;
> + }
> +
> + /* Add new bad chunk to list. */
> + bc->chunk_offset = em->start;
> + free_extent_map(em);
> +
> + INIT_LIST_HEAD(&bc->list);
> + list_add(&bc->list, &fs_info->bad_chunks);
> +
> + write_sequnlock_irqrestore(&fs_info->bc_lock, flags);
> + }
> }
>
> /*
> @@ -1320,6 +1371,8 @@ static noinline void finish_rmw(struct btrfs_raid_bio
> *rbio)
> bio->bi_end_io = raid_write_end_io;
> bio_set_op_attrs(bio, REQ_OP_WRITE, 0);
>
> + btrfs_bio_wq_end_io(rbio->fs_info, bio, BTRFS_WQ_ENDIO_RAID56);
> +
> submit_bio(bio);
> }
> return;
> @@ -2465,6 +2518,8 @@ static noinline void finish_parity_scrub(struct
> btrfs_raid_bio *rbio,
> bio->bi_end_io = raid_write_end_io;
> bio_set_op_attrs(bio, REQ_OP_WRITE, 0);
>
> + btrfs_bio_wq_end_io(rbio->fs_info, bio, BTRFS_WQ_ENDIO_RAID56);
> +
> submit_bio(bio);
> }
> return;
> diff --git a/fs/btrfs/sysfs.c b/fs/btrfs/sysfs.c
> index a28bba8..0baaa33 100644
> --- a/fs/btrfs/sysfs.c
> +++ b/fs/btrfs/sysfs.c
> @@ -490,12 +490,38 @@ static ssize_t quota_override_store(struct kobject
> *kobj,
>
> BTRFS_ATTR_RW(, quota_override, quota_override_show, quota_override_store);
>
> +static ssize_t btrfs_bad_chunks_show(struct kobject *kobj,
> + struct kobj_attribute *a, char *buf)
> +{
> + struct btrfs_fs_info *fs_info = to_fs_info(kobj);
> + struct btrfs_bad_chunk *bc;
> + int len = 0;
> + unsigned int seq;
> +
> + /* read lock please */
> + do {
> + seq = read_seqbegin(&fs_info->bc_lock);
> + list_for_each_entry(bc, &fs_info->bad_chunks, list) {
> + len += snprintf(buf + len, PAGE_SIZE - len, "%llu\n",
> + bc->chunk_offset);
> + /* chunk offset is u64 */
> + if (len >= PAGE_SIZE)
> + break;
> + }
> + } while (read_seqretry(&fs_info->bc_lock, seq));
> +
> + return len;
> +}
> +
> +BTRFS_ATTR(, bad_chunks, btrfs_bad_chunks_show);
> +
> static const struct attribute *btrfs_attrs[] = {
> BTRFS_ATTR_PTR(, label),
> BTRFS_ATTR_PTR(, nodesize),
> BTRFS_ATTR_PTR(, sectorsize),
> BTRFS_ATTR_PTR(, clone_alignment),
> BTRFS_ATTR_PTR(, quota_override),
> + BTRFS_ATTR_PTR(, bad_chunks),
> NULL,
> };
>
> diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
> index a256842..d71f11a 100644
> --- a/fs/btrfs/volumes.c
> +++ b/fs/btrfs/volumes.c
> @@ -2803,8 +2803,8 @@ static int btrfs_del_sys_chunk(struct btrfs_fs_info
> *fs_info, u64 chunk_offset)
> return ret;
> }
>
> -static struct extent_map *get_chunk_map(struct btrfs_fs_info *fs_info,
> - u64 logical, u64 length)
> +struct extent_map *get_chunk_map(struct btrfs_fs_info *fs_info,
> + u64 logical, u64 length)
> {
> struct extent_map_tree *em_tree;
> struct extent_map *em;
> @@ -2840,6 +2840,7 @@ int btrfs_remove_chunk(struct btrfs_trans_handle *trans,
> u64 dev_extent_len = 0;
> int i, ret = 0;
> struct btrfs_fs_devices *fs_devices = fs_info->fs_devices;
> + struct btrfs_bad_chunk *bc;
>
> em = get_chunk_map(fs_info, chunk_offset, 1);
> if (IS_ERR(em)) {
> @@ -2916,6 +2917,16 @@ int btrfs_remove_chunk(struct btrfs_trans_handle
> *trans,
> }
>
> out:
> + write_seqlock_irq(&fs_info->bc_lock);
> + list_for_each_entry(bc, &fs_info->bad_chunks, list) {
> + if (bc->chunk_offset == chunk_offset) {
> + list_del_init(&bc->list);
> + kfree(bc);
> + break;
> + }
> + }
> + write_sequnlock_irq(&fs_info->bc_lock);
> +
> /* once for us */
> free_extent_map(em);
> return ret;
> diff --git a/fs/btrfs/volumes.h b/fs/btrfs/volumes.h
> index ff15208..4e846ba 100644
> --- a/fs/btrfs/volumes.h
> +++ b/fs/btrfs/volumes.h
> @@ -396,6 +396,8 @@ static inline enum btrfs_map_op btrfs_op(struct bio *bio)
> }
> }
>
> +struct extent_map *get_chunk_map(struct btrfs_fs_info *fs_info,
> + u64 logical, u64 length);
> int btrfs_account_dev_extents_size(struct btrfs_device *device, u64 start,
> u64 end, u64 *length);
> void btrfs_get_bbio(struct btrfs_bio *bbio);
> --
> 2.9.4
>
> --
> To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in
> the body of a message to majord...@vger.kernel.org
> More majordomo info at http://vger.kernel.org/majordomo-info.html
--
To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in
the body of a message to majord...@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
