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bcachefs: Check for extents that point to same space
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In backpointer repair, if we get a missing backpointer - but there's
already a backpointer that points to an existing extent - we've got
multiple extents that point to the same space and need to decide which
to keep.

Signed-off-by: Kent Overstreet <[email protected]>
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Kent Overstreet committed Apr 3, 2024
1 parent a292be3 commit 4c02e63
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Showing 2 changed files with 168 additions and 8 deletions.
173 changes: 166 additions & 7 deletions fs/bcachefs/backpointers.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -8,6 +8,7 @@
#include "btree_update.h"
#include "btree_update_interior.h"
#include "btree_write_buffer.h"
#include "checksum.h"
#include "error.h"

#include <linux/mm.h>
Expand Down Expand Up @@ -418,28 +419,113 @@ struct extents_to_bp_state {
struct bkey_buf last_flushed;
};

static int drop_dev_and_update(struct btree_trans *trans, enum btree_id btree,
struct bkey_s_c extent, unsigned dev)
{
struct bkey_i *n = bch2_bkey_make_mut_noupdate(trans, extent);
int ret = PTR_ERR_OR_ZERO(n);
if (ret)
return ret;

bch2_bkey_drop_device(bkey_i_to_s(n), dev);
return bch2_btree_insert_trans(trans, btree, n, 0);
}

static int check_extent_checksum(struct btree_trans *trans,
enum btree_id btree, struct bkey_s_c extent,
enum btree_id o_btree, struct bkey_s_c extent2, unsigned dev)
{
struct bch_fs *c = trans->c;
struct bkey_ptrs_c ptrs = bch2_bkey_ptrs_c(extent);
const union bch_extent_entry *entry;
struct extent_ptr_decoded p;
struct printbuf buf = PRINTBUF;
void *data_buf = NULL;
struct bio *bio = NULL;
size_t bytes;
int ret = 0;

if (bkey_is_btree_ptr(extent.k))
return false;

bkey_for_each_ptr_decode(extent.k, ptrs, p, entry)
if (p.ptr.dev == dev)
goto found;
BUG();
found:
if (!p.crc.csum_type)
return false;

bytes = p.crc.compressed_size << 9;

struct bch_dev *ca = bch_dev_bkey_exists(c, dev);
if (!bch2_dev_get_ioref(ca, READ))
return false;

data_buf = kvmalloc(bytes, GFP_KERNEL);
if (!data_buf) {
ret = -ENOMEM;
goto err;
}

bio = bio_alloc(ca->disk_sb.bdev, 1, REQ_OP_READ, GFP_KERNEL);
bio->bi_iter.bi_sector = p.ptr.offset;
bch2_bio_map(bio, data_buf, bytes);
ret = submit_bio_wait(bio);
if (ret)
goto err;

prt_str(&buf, "extents pointing to same space, but first extent checksum bad:");
prt_printf(&buf, "\n %s ", bch2_btree_id_str(btree));
bch2_bkey_val_to_text(&buf, c, extent);
prt_printf(&buf, "\n %s ", bch2_btree_id_str(o_btree));
bch2_bkey_val_to_text(&buf, c, extent2);

struct nonce nonce = extent_nonce(extent.k->version, p.crc);
struct bch_csum csum = bch2_checksum(c, p.crc.csum_type, nonce, data_buf, bytes);
if (fsck_err_on(bch2_crc_cmp(csum, p.crc.csum),
c, dup_backpointer_to_bad_csum_extent,
"%s", buf.buf))
ret = drop_dev_and_update(trans, btree, extent, dev) ?: 1;
fsck_err:
err:
if (bio)
bio_put(bio);
kvfree(data_buf);
percpu_ref_put(&ca->io_ref);
printbuf_exit(&buf);
return ret;
}

static int check_bp_exists(struct btree_trans *trans,
struct extents_to_bp_state *s,
struct bpos bucket,
struct bch_backpointer bp,
struct bkey_s_c orig_k)
{
struct bch_fs *c = trans->c;
struct btree_iter bp_iter = { NULL };
struct btree_iter bp_iter = {};
struct btree_iter other_extent_iter = {};
struct printbuf buf = PRINTBUF;
struct bkey_s_c bp_k;
struct bkey_buf tmp;
int ret;

bch2_bkey_buf_init(&tmp);

if (!bch2_dev_bucket_exists(c, bucket)) {
prt_str(&buf, "extent for nonexistent device:bucket ");
bch2_bpos_to_text(&buf, bucket);
prt_str(&buf, "\n ");
bch2_bkey_val_to_text(&buf, c, orig_k);
bch_err(c, "%s", buf.buf);
return -BCH_ERR_fsck_repair_unimplemented;
}

if (bpos_lt(bucket, s->bucket_start) ||
bpos_gt(bucket, s->bucket_end))
return 0;

if (!bch2_dev_bucket_exists(c, bucket))
goto missing;

bp_k = bch2_bkey_get_iter(trans, &bp_iter, BTREE_ID_backpointers,
bucket_pos_to_bp(c, bucket, bp.bucket_offset),
0);
Expand All @@ -465,21 +551,94 @@ static int check_bp_exists(struct btree_trans *trans,
ret = -BCH_ERR_transaction_restart_write_buffer_flush;
goto out;
}
goto missing;

goto check_existing_bp;
}
out:
err:
fsck_err:
bch2_trans_iter_exit(trans, &other_extent_iter);
bch2_trans_iter_exit(trans, &bp_iter);
bch2_bkey_buf_exit(&tmp, c);
printbuf_exit(&buf);
return ret;
check_existing_bp:
/* Do we have a backpointer for a different extent? */
if (bp_k.k->type != KEY_TYPE_backpointer)
goto missing;

struct bch_backpointer other_bp = *bkey_s_c_to_backpointer(bp_k).v;

struct bkey_s_c other_extent =
bch2_backpointer_get_key(trans, &other_extent_iter, bp_k.k->p, other_bp, 0);
ret = bkey_err(other_extent);
if (ret == -BCH_ERR_backpointer_to_overwritten_btree_node)
ret = 0;
if (ret)
goto err;

if (!other_extent.k)
goto missing;

if (bch2_extents_match(orig_k, other_extent)) {
printbuf_reset(&buf);
prt_printf(&buf, "duplicate versions of same extent, deleting smaller\n ");
bch2_bkey_val_to_text(&buf, c, orig_k);
prt_str(&buf, "\n ");
bch2_bkey_val_to_text(&buf, c, other_extent);
bch_err(c, "%s", buf.buf);

if (other_extent.k->size <= orig_k.k->size) {
ret = drop_dev_and_update(trans, other_bp.btree_id, other_extent, bucket.inode);
if (ret)
goto err;
goto out;
} else {
ret = drop_dev_and_update(trans, bp.btree_id, orig_k, bucket.inode);
if (ret)
goto err;
goto missing;
}
}

ret = check_extent_checksum(trans, other_bp.btree_id, other_extent, bp.btree_id, orig_k, bucket.inode);
if (ret < 0)
goto err;
if (ret) {
ret = 0;
goto missing;
}

ret = check_extent_checksum(trans, bp.btree_id, orig_k, other_bp.btree_id, other_extent, bucket.inode);
if (ret < 0)
goto err;
if (ret) {
ret = 0;
goto out;
}

printbuf_reset(&buf);
prt_printf(&buf, "duplicate extents pointing to same space on dev %llu\n ", bucket.inode);
bch2_bkey_val_to_text(&buf, c, orig_k);
prt_str(&buf, "\n ");
bch2_bkey_val_to_text(&buf, c, other_extent);
bch_err(c, "%s", buf.buf);
ret = -BCH_ERR_fsck_repair_unimplemented;
goto err;
missing:
printbuf_reset(&buf);
prt_printf(&buf, "missing backpointer for btree=%s l=%u ",
bch2_btree_id_str(bp.btree_id), bp.level);
bch2_bkey_val_to_text(&buf, c, orig_k);
prt_printf(&buf, "\nbp pos ");
bch2_bpos_to_text(&buf, bp_iter.pos);
prt_printf(&buf, "\n got: ");
bch2_bkey_val_to_text(&buf, c, bp_k);

struct bkey_i_backpointer n_bp_k;
bkey_backpointer_init(&n_bp_k.k_i);
n_bp_k.k.p = bucket_pos_to_bp(trans->c, bucket, bp.bucket_offset);
n_bp_k.v = bp;
prt_printf(&buf, "\n want: ");
bch2_bkey_val_to_text(&buf, c, bkey_i_to_s_c(&n_bp_k.k_i));

if (fsck_err(c, ptr_to_missing_backpointer, "%s", buf.buf))
ret = bch2_bucket_backpointer_mod(trans, bucket, bp, orig_k, true);
Expand Down
3 changes: 2 additions & 1 deletion fs/bcachefs/sb-errors_types.h
View file
Original file line number Diff line number Diff line change
Expand Up @@ -269,7 +269,8 @@
x(btree_node_topology_empty_interior_node, 261) \
x(btree_ptr_v2_min_key_bad, 262) \
x(btree_root_unreadable_and_scan_found_nothing, 263) \
x(snapshot_node_missing, 264)
x(snapshot_node_missing, 264) \
x(dup_backpointer_to_bad_csum_extent, 265)

enum bch_sb_error_id {
#define x(t, n) BCH_FSCK_ERR_##t = n,
Expand Down

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