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Extend zdb to print inconsistencies in livelists and metaslabs

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Livelists and spacemaps are data structures that are logs of allocations
and frees.  Livelists entries are block pointers (blkptr_t). Spacemaps
entries are ranges of numbers, most often used as to track
allocated/freed regions of metaslabs/vdevs.

These data structures can become self-inconsistent, for example if a
block or range can be "double allocated" (two allocation records without
an intervening free) or "double freed" (two free records without an
intervening allocation).

ZDB (as well as zfs running in the kernel) can detect these
inconsistencies when loading livelists and metaslab.  However, it
generally halts processing when the error is detected.

When analyzing an on-disk problem, we often want to know the entire set
of inconsistencies, which is not possible with the current behavior.
This commit adds a new flag, `zdb -y`, which analyzes the livelist and
metaslab data structures and displays all of their inconsistencies.
Note that this is different from the leak detection performed by
`zdb -b`, which checks for inconsistencies between the spacemaps and the
tree of block pointers, but assumes the spacemaps are self-consistent.

The specific checks added are:

Verify livelists by iterating through each sublivelists and:
- report leftover FREEs
- report double ALLOCs and double FREEs
- record leftover ALLOCs together with their TXG [see Cross Check]

Verify spacemaps by iterating over each metaslab and:
- iterate over spacemap and then the metaslab's entries in the
  spacemap log, then report any double FREEs and double ALLOCs

Verify that livelists are consistenet with spacemaps.  The space
referenced by livelists (after using the FREE's to cancel out
corresponding ALLOCs) should be allocated, according to the spacemaps.

Reviewed-by: Serapheim Dimitropoulos <serapheim@delphix.com>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Co-authored-by: Sara Hartse <sara.hartse@delphix.com>
Signed-off-by: Matthew Ahrens <mahrens@delphix.com>
External-issue: DLPX-66031
Closes #10515
This commit is contained in:
Matthew Ahrens
2020-07-14 17:51:05 -07:00
committed by GitHub
parent 38e2e9ce83
commit 6774931dfa
9 changed files with 649 additions and 65 deletions
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module/zfs/space_map.c
+26 -2
View File
@@ -96,6 +96,7 @@ space_map_iterate(space_map_t *sm, uint64_t end, sm_cb_t callback, void *arg)
ZIO_PRIORITY_SYNC_READ);
int error = 0;
uint64_t txg = 0, sync_pass = 0;
for (uint64_t block_base = 0; block_base < end && error == 0;
block_base += blksz) {
dmu_buf_t *db;
@@ -117,8 +118,29 @@ space_map_iterate(space_map_t *sm, uint64_t end, sm_cb_t callback, void *arg)
block_cursor < block_end && error == 0; block_cursor++) {
uint64_t e = *block_cursor;
if (sm_entry_is_debug(e)) /* Skip debug entries */
if (sm_entry_is_debug(e)) {
/*
* Debug entries are only needed to record the
* current TXG and sync pass if available.
*
* Note though that sometimes there can be
* debug entries that are used as padding
* at the end of space map blocks in-order
* to not split a double-word entry in the
* middle between two blocks. These entries
* have their TXG field set to 0 and we
* skip them without recording the TXG.
* [see comment in space_map_write_seg()]
*/
uint64_t e_txg = SM_DEBUG_TXG_DECODE(e);
if (e_txg != 0) {
txg = e_txg;
sync_pass = SM_DEBUG_SYNCPASS_DECODE(e);
} else {
ASSERT0(SM_DEBUG_SYNCPASS_DECODE(e));
}
continue;
}
uint64_t raw_offset, raw_run, vdev_id;
maptype_t type;
@@ -158,7 +180,9 @@ space_map_iterate(space_map_t *sm, uint64_t end, sm_cb_t callback, void *arg)
.sme_type = type,
.sme_vdev = vdev_id,
.sme_offset = entry_offset,
.sme_run = entry_run
.sme_run = entry_run,
.sme_txg = txg,
.sme_sync_pass = sync_pass
};
error = callback(&sme, arg);
}