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MDEV-30753 Possible corruption due to trx_purge_free_segment()

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Starting with commit 0de3be8cfd (MDEV-30671),
the field TRX_UNDO_NEEDS_PURGE lost its previous meaning.
The following scenario is possible:

(1) InnoDB is killed at a point of time corresponding to the durable
execution of some fseg_free_step_not_header() but not
trx_purge_remove_log_hdr().
(2) After restart, the affected pages are allocated for something else.
(3) Purge will attempt to access the newly reallocated pages when looking
for some old undo log records.

trx_purge_free_segment(): Invoke trx_purge_remove_log_hdr() as the first
thing, to be safe. If the server is killed, some pages will never be
freed. That is the lesser evil. Also, before each mtr.start(), invoke
log_free_check() to prevent ib_logfile0 overrun.
This commit is contained in:
Marko Mäkelä 2023-02-28 15:39:23 +02:00
parent 57c526ffb8
commit c14a39431b
2 changed files with 35 additions and 55 deletions
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1
storage/innobase/include/log0log.inl
View file

@ -306,6 +306,7 @@ log_free_check(void)
#ifdef UNIV_DEBUG
static const latch_level_t latches[] = {
SYNC_REDO_RSEG, /* trx_purge_free_segment() */
SYNC_DICT, /* dict_sys.mutex during
commit_try_rebuild() */
SYNC_DICT_OPERATION, /* dict_sys.latch X-latch during

89
storage/innobase/trx/trx0purge.cc
View file

@ -345,66 +345,45 @@ static void trx_purge_remove_log_hdr(buf_block_t *rseg, buf_block_t* log,
static
void trx_purge_free_segment(mtr_t &mtr, trx_rseg_t* rseg, fil_addr_t hdr_addr)
{
mtr.commit();
mtr.start();
ut_ad(mutex_own(&rseg->mutex));
mtr.commit();
log_free_check();
mtr.start();
ut_ad(mutex_own(&rseg->mutex));
buf_block_t* rseg_hdr = trx_rsegf_get(rseg->space, rseg->page_no, &mtr);
buf_block_t* block = trx_undo_page_get(
page_id_t(rseg->space->id, hdr_addr.page), &mtr);
buf_block_t *rseg_hdr= trx_rsegf_get(rseg->space, rseg->page_no, &mtr);
buf_block_t *block=
trx_undo_page_get(page_id_t(rseg->space->id, hdr_addr.page), &mtr);
const uint32_t seg_size=
flst_get_len(TRX_UNDO_SEG_HDR + TRX_UNDO_PAGE_LIST + block->frame);
ut_ad(rseg->curr_size >= seg_size);
rseg->curr_size-= seg_size;
/* Mark the last undo log totally purged, so that if the
system crashes, the tail of the undo log will not get accessed
again. The list of pages in the undo log tail gets
inconsistent during the freeing of the segment, and therefore
purge should not try to access them again. */
mtr.write<2,mtr_t::MAYBE_NOP>(*block, block->frame + hdr_addr.boffset
+ TRX_UNDO_NEEDS_PURGE, 0U);
trx_purge_remove_log_hdr(rseg_hdr, block, hdr_addr.boffset, &mtr);
byte *hist= TRX_RSEG + TRX_RSEG_HISTORY_SIZE + rseg_hdr->frame;
ut_ad(mach_read_from_4(hist) >= seg_size);
mtr.write<4>(*rseg_hdr, hist, mach_read_from_4(hist) - seg_size);
while (!fseg_free_step_not_header(
TRX_UNDO_SEG_HDR + TRX_UNDO_FSEG_HEADER
+ block->frame, &mtr)) {
mtr.commit();
mtr.start();
while (!fseg_free_step_not_header(TRX_UNDO_SEG_HDR + TRX_UNDO_FSEG_HEADER +
block->frame, &mtr))
{
block->fix();
mtr.commit();
/* NOTE: If the server is killed after the log that was produced
up to this point was written, and before the log from the mtr.commit()
in our caller is written, then the pages belonging to the
undo log will become unaccessible garbage.
rseg_hdr = trx_rsegf_get(rseg->space, rseg->page_no, &mtr);
This does not matters when using multiple innodb_undo_tablespaces;
innodb_undo_log_truncate=ON will be able to reclaim the space. */
log_free_check();
mtr.start();
ut_ad(rw_lock_s_lock_nowait(block->debug_latch, __FILE__, __LINE__));
rw_lock_x_lock(&block->lock);
mtr_memo_push(&mtr, block, MTR_MEMO_PAGE_X_FIX);
}
block = trx_undo_page_get(
page_id_t(rseg->space->id, hdr_addr.page), &mtr);
}
/* The page list may now be inconsistent, but the length field
stored in the list base node tells us how big it was before we
started the freeing. */
const uint32_t seg_size = flst_get_len(
TRX_UNDO_SEG_HDR + TRX_UNDO_PAGE_LIST + block->frame);
/* We may free the undo log segment header page; it must be freed
within the same mtr as the undo log header is removed from the
history list: otherwise, in case of a database crash, the segment
could become inaccessible garbage in the file space. */
trx_purge_remove_log_hdr(rseg_hdr, block, hdr_addr.boffset, &mtr);
do {
/* Here we assume that a file segment with just the header
page can be freed in a few steps, so that the buffer pool
is not flooded with bufferfixed pages: see the note in
fsp0fsp.cc. */
} while (!fseg_free_step(TRX_UNDO_SEG_HDR + TRX_UNDO_FSEG_HEADER
+ block->frame, &mtr));
byte* hist = TRX_RSEG + TRX_RSEG_HISTORY_SIZE + rseg_hdr->frame;
ut_ad(mach_read_from_4(hist) >= seg_size);
mtr.write<4>(*rseg_hdr, hist, mach_read_from_4(hist) - seg_size);
ut_ad(rseg->curr_size >= seg_size);
rseg->curr_size -= seg_size;
while (!fseg_free_step(TRX_UNDO_SEG_HDR + TRX_UNDO_FSEG_HEADER +
block->frame, &mtr));
}
/** Remove unnecessary history data from a rollback segment.