From: Ye Bin <[email protected]>
This series hardens dm-persistent-data against metadata corruption that
can leave the kernel hung in an uninterruptible state. The two patches
attack the same class of problem from both sides: symptom detection and
root-cause prevention.
Patch 1 adds a depth limit (DM_BTREE_MAX_DEPTH = 16) to every unbounded
btree traversal loop (lookup, insert, overwrite, remove, find_key).
When metadata is corrupted such that a node's value points back to an
ancestor or to itself, these loops currently never terminate, hanging
the kernel. With the limit in place the traversal returns -ELOOP
instead, and dm-thin handles this error by aborting the transaction and
downgrading the pool to read-only mode so no further writes hit the
corrupted metadata.
Patch 2 addresses a root cause of such corruption. The transaction
manager's dm_tm_inc/dm_tm_dec/dm_tm_inc_range/dm_tm_dec_range wrappers
have void return types, so when the underlying space-map operations
fail the error is silently swallowed and the transaction is committed
with inconsistent reference counts. This can produce permanent space
leaks, premature refcount drops, and -- critically -- self-referencing
btree nodes that trigger the very infinite loops that patch 1 catches.
The fix records the first space-map failure in a sticky error flag
(sm_error in the transaction manager, data_sm_error in dm_pool_metadata)
and refuses to commit while the flag is set, all without changing any
function signatures.
Ye Bin (2):
dm persistent-data: add btree traversal depth limit to detect metadata
corruption
dm persistent-data: record space-map errors in transaction manager
drivers/md/dm-thin-metadata.c | 65 +++++++++++++---
drivers/md/dm-thin.c | 9 +++
drivers/md/persistent-data/dm-btree-remove.c | 14 ++++
drivers/md/persistent-data/dm-btree.c | 28 +++++++
drivers/md/persistent-data/dm-btree.h | 8 ++
.../persistent-data/dm-transaction-manager.c | 74 ++++++++++++++++++-
.../persistent-data/dm-transaction-manager.h | 6 ++
7 files changed, 191 insertions(+), 13 deletions(-)
--
2.34.1
