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mariadb/storage/innobase/include/btr0pcur.inl
Vlad Lesin c0eda62aec MDEV-27927 row_sel_try_search_shortcut_for_mysql() does not latch a page, violating read view isolation 
btr_search_guess_on_hash() would only acquire an index page latch if it
is invoked with ahi_latch=NULL. If it's invoked from
row_sel_try_search_shortcut_for_mysql() with ahi_latch!=NULL, a page
will not be latched, and row_search_mvcc() will get a pointer to the
record, which can be changed by some other transaction before the record
was stored in result buffer with row_sel_store_mysql_rec() call.

ahi_latch argument of btr_cur_search_to_nth_level_func() and
btr_pcur_open_with_no_init_func() is used only for
row_sel_try_search_shortcut_for_mysql().
btr_cur_search_to_nth_level_func(..., ahi_latch !=0, ...) is invoked
only from btr_pcur_open_with_no_init_func(..., ahi_latch !=0, ...),
which, in turns, is invoked only from
row_sel_try_search_shortcut_for_mysql().

I suppose that separate case with ahi_latch!=0 was intentionally
implemented to protect row_sel_store_mysql_rec() call in
row_search_mvcc() just after row_sel_try_search_shortcut_for_mysql()
call. After the ahi_latch was moved from row_seach_mvcc() to
row_sel_try_search_shortcut_for_mysql(), there is no need in it at all
if btr_search_guess_on_hash() latches a page unconditionally. And if
btr_search_guess_on_hash() latched the page, any access to the record in
row_sel_try_search_shortcut_for_mysql() after btr_pcur_open_with_no_init()
call will be protected with the page latch.

The fix is to remove ahi_latch argument from
btr_pcur_open_with_no_init_func(), btr_cur_search_to_nth_level_func()
and btr_search_guess_on_hash().

There will not be test, as to test it we need to freeze some SELECT
execution in the point between row_sel_try_search_shortcut_for_mysql()
and row_sel_store_mysql_rec() calls in row_search_mvcc(), and to change
the record in some other transaction to let row_sel_store_mysql_rec() to
store changed record in result buffer. Buf we can't do this with the
fix, as the page will be latched in btr_search_guess_on_hash() call.
2022-10-05 17:35:21 +03:00

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/*****************************************************************************
Copyright (c) 1996, 2015, Oracle and/or its affiliates. All Rights Reserved.
Copyright (c) 2015, 2020, MariaDB Corporation.
This program is free software; you can redistribute it and/or modify it under
the terms of the GNU General Public License as published by the Free Software
Foundation; version 2 of the License.
This program is distributed in the hope that it will be useful, but WITHOUT
ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details.
You should have received a copy of the GNU General Public License along with
this program; if not, write to the Free Software Foundation, Inc.,
51 Franklin Street, Fifth Floor, Boston, MA 02110-1335 USA
*****************************************************************************/
/**************************************************//**
@file include/btr0pcur.ic
The index tree persistent cursor
Created 2/23/1996 Heikki Tuuri
*******************************************************/
/*********************************************************//**
Gets the rel_pos field for a cursor whose position has been stored.
@return BTR_PCUR_ON, ... */
UNIV_INLINE
ulint
btr_pcur_get_rel_pos(
/*=================*/
const btr_pcur_t* cursor) /*!< in: persistent cursor */
{
ut_ad(cursor);
ut_ad(cursor->old_rec);
ut_ad(cursor->old_stored);
ut_ad(cursor->pos_state == BTR_PCUR_WAS_POSITIONED
|| cursor->pos_state == BTR_PCUR_IS_POSITIONED);
return(cursor->rel_pos);
}
#ifdef UNIV_DEBUG
/*********************************************************//**
Returns the btr cursor component of a persistent cursor.
@return pointer to btr cursor component */
UNIV_INLINE
btr_cur_t*
btr_pcur_get_btr_cur(
/*=================*/
const btr_pcur_t* cursor) /*!< in: persistent cursor */
{
const btr_cur_t* btr_cur = &cursor->btr_cur;
return((btr_cur_t*) btr_cur);
}
/*********************************************************//**
Returns the page cursor component of a persistent cursor.
@return pointer to page cursor component */
UNIV_INLINE
page_cur_t*
btr_pcur_get_page_cur(
/*==================*/
const btr_pcur_t* cursor) /*!< in: persistent cursor */
{
return(btr_cur_get_page_cur(btr_pcur_get_btr_cur(cursor)));
}
/*********************************************************//**
Returns the page of a persistent cursor.
@return pointer to the page */
UNIV_INLINE
page_t*
btr_pcur_get_page(
/*==============*/
const btr_pcur_t* cursor) /*!< in: persistent cursor */
{
ut_ad(cursor->pos_state == BTR_PCUR_IS_POSITIONED);
return(btr_cur_get_page(btr_pcur_get_btr_cur(cursor)));
}
/*********************************************************//**
Returns the buffer block of a persistent cursor.
@return pointer to the block */
UNIV_INLINE
buf_block_t*
btr_pcur_get_block(
/*===============*/
const btr_pcur_t* cursor) /*!< in: persistent cursor */
{
ut_ad(cursor->pos_state == BTR_PCUR_IS_POSITIONED);
return(btr_cur_get_block(btr_pcur_get_btr_cur(cursor)));
}
/*********************************************************//**
Returns the record of a persistent cursor.
@return pointer to the record */
UNIV_INLINE
rec_t*
btr_pcur_get_rec(
/*=============*/
const btr_pcur_t* cursor) /*!< in: persistent cursor */
{
ut_ad(cursor->pos_state == BTR_PCUR_IS_POSITIONED);
ut_ad(cursor->latch_mode != BTR_NO_LATCHES);
return(btr_cur_get_rec(btr_pcur_get_btr_cur(cursor)));
}
#endif /* UNIV_DEBUG */
/**************************************************************//**
Gets the up_match value for a pcur after a search.
@return number of matched fields at the cursor or to the right if
search mode was PAGE_CUR_GE, otherwise undefined */
UNIV_INLINE
ulint
btr_pcur_get_up_match(
/*==================*/
const btr_pcur_t* cursor) /*!< in: persistent cursor */
{
const btr_cur_t* btr_cursor;
ut_ad((cursor->pos_state == BTR_PCUR_WAS_POSITIONED)
|| (cursor->pos_state == BTR_PCUR_IS_POSITIONED));
btr_cursor = btr_pcur_get_btr_cur(cursor);
ut_ad(btr_cursor->up_match != ULINT_UNDEFINED);
return(btr_cursor->up_match);
}
/**************************************************************//**
Gets the low_match value for a pcur after a search.
@return number of matched fields at the cursor or to the right if
search mode was PAGE_CUR_LE, otherwise undefined */
UNIV_INLINE
ulint
btr_pcur_get_low_match(
/*===================*/
const btr_pcur_t* cursor) /*!< in: persistent cursor */
{
const btr_cur_t* btr_cursor;
ut_ad((cursor->pos_state == BTR_PCUR_WAS_POSITIONED)
|| (cursor->pos_state == BTR_PCUR_IS_POSITIONED));
btr_cursor = btr_pcur_get_btr_cur(cursor);
ut_ad(btr_cursor->low_match != ULINT_UNDEFINED);
return(btr_cursor->low_match);
}
/*********************************************************//**
Checks if the persistent cursor is after the last user record on
a page. */
UNIV_INLINE
ibool
btr_pcur_is_after_last_on_page(
/*===========================*/
const btr_pcur_t* cursor) /*!< in: persistent cursor */
{
ut_ad(cursor->pos_state == BTR_PCUR_IS_POSITIONED);
ut_ad(cursor->latch_mode != BTR_NO_LATCHES);
return(page_cur_is_after_last(btr_pcur_get_page_cur(cursor)));
}
/*********************************************************//**
Checks if the persistent cursor is before the first user record on
a page. */
UNIV_INLINE
ibool
btr_pcur_is_before_first_on_page(
/*=============================*/
const btr_pcur_t* cursor) /*!< in: persistent cursor */
{
ut_ad(cursor->pos_state == BTR_PCUR_IS_POSITIONED);
ut_ad(cursor->latch_mode != BTR_NO_LATCHES);
return(page_cur_is_before_first(btr_pcur_get_page_cur(cursor)));
}
/*********************************************************//**
Checks if the persistent cursor is on a user record. */
UNIV_INLINE
ibool
btr_pcur_is_on_user_rec(
/*====================*/
const btr_pcur_t* cursor) /*!< in: persistent cursor */
{
ut_ad(cursor->pos_state == BTR_PCUR_IS_POSITIONED);
ut_ad(cursor->latch_mode != BTR_NO_LATCHES);
if (btr_pcur_is_before_first_on_page(cursor)
|| btr_pcur_is_after_last_on_page(cursor)) {
return(FALSE);
}
return(TRUE);
}
/*********************************************************//**
Checks if the persistent cursor is before the first user record in
the index tree. */
static inline bool btr_pcur_is_before_first_in_tree(btr_pcur_t* cursor)
{
ut_ad(cursor->pos_state == BTR_PCUR_IS_POSITIONED);
ut_ad(cursor->latch_mode != BTR_NO_LATCHES);
return !page_has_prev(btr_pcur_get_page(cursor))
&& page_cur_is_before_first(btr_pcur_get_page_cur(cursor));
}
/*********************************************************//**
Checks if the persistent cursor is after the last user record in
the index tree. */
static inline bool btr_pcur_is_after_last_in_tree(btr_pcur_t* cursor)
{
ut_ad(cursor->pos_state == BTR_PCUR_IS_POSITIONED);
ut_ad(cursor->latch_mode != BTR_NO_LATCHES);
return !page_has_next(btr_pcur_get_page(cursor))
&& page_cur_is_after_last(btr_pcur_get_page_cur(cursor));
}
/*********************************************************//**
Moves the persistent cursor to the next record on the same page. */
UNIV_INLINE
void
btr_pcur_move_to_next_on_page(
/*==========================*/
btr_pcur_t* cursor) /*!< in/out: persistent cursor */
{
ut_ad(cursor->pos_state == BTR_PCUR_IS_POSITIONED);
ut_ad(cursor->latch_mode != BTR_NO_LATCHES);
page_cur_move_to_next(btr_pcur_get_page_cur(cursor));
cursor->old_stored = false;
}
/*********************************************************//**
Moves the persistent cursor to the previous record on the same page. */
UNIV_INLINE
void
btr_pcur_move_to_prev_on_page(
/*==========================*/
btr_pcur_t* cursor) /*!< in/out: persistent cursor */
{
ut_ad(cursor->pos_state == BTR_PCUR_IS_POSITIONED);
ut_ad(cursor->latch_mode != BTR_NO_LATCHES);
page_cur_move_to_prev(btr_pcur_get_page_cur(cursor));
cursor->old_stored = false;
}
/*********************************************************//**
Moves the persistent cursor to the next user record in the tree. If no user
records are left, the cursor ends up 'after last in tree'.
@return TRUE if the cursor moved forward, ending on a user record */
UNIV_INLINE
ibool
btr_pcur_move_to_next_user_rec(
/*===========================*/
btr_pcur_t* cursor, /*!< in: persistent cursor; NOTE that the
function may release the page latch */
mtr_t* mtr) /*!< in: mtr */
{
ut_ad(cursor->pos_state == BTR_PCUR_IS_POSITIONED);
ut_ad(cursor->latch_mode != BTR_NO_LATCHES);
cursor->old_stored = false;
loop:
if (btr_pcur_is_after_last_on_page(cursor)) {
if (btr_pcur_is_after_last_in_tree(cursor)) {
return(FALSE);
}
btr_pcur_move_to_next_page(cursor, mtr);
} else {
btr_pcur_move_to_next_on_page(cursor);
}
if (btr_pcur_is_on_user_rec(cursor)) {
return(TRUE);
}
goto loop;
}
/*********************************************************//**
Moves the persistent cursor to the next record in the tree. If no records are
left, the cursor stays 'after last in tree'.
@return TRUE if the cursor was not after last in tree */
UNIV_INLINE
ibool
btr_pcur_move_to_next(
/*==================*/
btr_pcur_t* cursor, /*!< in: persistent cursor; NOTE that the
function may release the page latch */
mtr_t* mtr) /*!< in: mtr */
{
ut_ad(cursor->pos_state == BTR_PCUR_IS_POSITIONED);
ut_ad(cursor->latch_mode != BTR_NO_LATCHES);
cursor->old_stored = false;
if (btr_pcur_is_after_last_on_page(cursor)) {
if (btr_pcur_is_after_last_in_tree(cursor)) {
return(FALSE);
}
btr_pcur_move_to_next_page(cursor, mtr);
return(TRUE);
}
btr_pcur_move_to_next_on_page(cursor);
return(TRUE);
}
/**************************************************************//**
Commits the mtr and sets the pcur latch mode to BTR_NO_LATCHES,
that is, the cursor becomes detached.
Function btr_pcur_store_position should be used before calling this,
if restoration of cursor is wanted later. */
UNIV_INLINE
void
btr_pcur_commit_specify_mtr(
/*========================*/
btr_pcur_t* pcur, /*!< in: persistent cursor */
mtr_t* mtr) /*!< in: mtr to commit */
{
ut_ad(pcur->pos_state == BTR_PCUR_IS_POSITIONED);
pcur->latch_mode = BTR_NO_LATCHES;
mtr_commit(mtr);
pcur->pos_state = BTR_PCUR_WAS_POSITIONED;
}
/** Commits the mtr and sets the clustered index pcur and secondary index
pcur latch mode to BTR_NO_LATCHES, that is, the cursor becomes detached.
Function btr_pcur_store_position should be used for both cursor before
calling this, if restoration of cursor is wanted later.
@param[in] pcur persistent cursor
@param[in] sec_pcur secondary index persistent cursor
@param[in] mtr mtr to commit */
UNIV_INLINE
void
btr_pcurs_commit_specify_mtr(
btr_pcur_t* pcur,
btr_pcur_t* sec_pcur,
mtr_t* mtr)
{
ut_ad(pcur->pos_state == BTR_PCUR_IS_POSITIONED);
ut_ad(sec_pcur->pos_state == BTR_PCUR_IS_POSITIONED);
pcur->latch_mode = BTR_NO_LATCHES;
sec_pcur->latch_mode = BTR_NO_LATCHES;
mtr_commit(mtr);
pcur->pos_state = BTR_PCUR_WAS_POSITIONED;
sec_pcur->pos_state = BTR_PCUR_WAS_POSITIONED;
}
/**************************************************************//**
Sets the old_rec_buf field to NULL. */
UNIV_INLINE
void
btr_pcur_init(
/*==========*/
btr_pcur_t* pcur) /*!< in: persistent cursor */
{
pcur->old_stored = false;
pcur->old_rec_buf = NULL;
pcur->old_rec = NULL;
pcur->btr_cur.rtr_info = NULL;
}
/** Free old_rec_buf.
@param[in] pcur Persistent cursor holding old_rec to be freed. */
UNIV_INLINE
void
btr_pcur_free(
btr_pcur_t* pcur)
{
ut_free(pcur->old_rec_buf);
}
/**************************************************************//**
Initializes and opens a persistent cursor to an index tree. It should be
closed with btr_pcur_close. */
UNIV_INLINE
dberr_t
btr_pcur_open_low(
/*==============*/
dict_index_t* index, /*!< in: index */
ulint level, /*!< in: level in the btree */
const dtuple_t* tuple, /*!< in: tuple on which search done */
page_cur_mode_t mode, /*!< in: PAGE_CUR_L, ...;
NOTE that if the search is made using a unique
prefix of a record, mode should be
PAGE_CUR_LE, not PAGE_CUR_GE, as the latter
may end up on the previous page from the
record! */
ulint latch_mode,/*!< in: BTR_SEARCH_LEAF, ... */
btr_pcur_t* cursor, /*!< in: memory buffer for persistent cursor */
const char* file, /*!< in: file name */
unsigned line, /*!< in: line where called */
ib_uint64_t autoinc,/*!< in: PAGE_ROOT_AUTO_INC to be written
(0 if none) */
mtr_t* mtr) /*!< in: mtr */
{
btr_cur_t* btr_cursor;
dberr_t err = DB_SUCCESS;
/* Initialize the cursor */
btr_pcur_init(cursor);
cursor->latch_mode = BTR_LATCH_MODE_WITHOUT_FLAGS(latch_mode);
cursor->search_mode = mode;
/* Search with the tree cursor */
btr_cursor = btr_pcur_get_btr_cur(cursor);
ut_ad(!dict_index_is_spatial(index));
err = btr_cur_search_to_nth_level(
index, level, tuple, mode, latch_mode, btr_cursor,
file, line, mtr, autoinc);
if (UNIV_UNLIKELY(err != DB_SUCCESS)) {
ib::warn() << "btr_pcur_open_low"
<< " level: " << level
<< " called from file: "
<< file << " line: " << line
<< " table: " << index->table->name
<< " index: " << index->name
<< " error: " << err;
}
cursor->pos_state = BTR_PCUR_IS_POSITIONED;
cursor->trx_if_known = NULL;
return(err);
}
/** Opens an persistent cursor to an index tree without initializing the
cursor.
@param index index
@param tuple tuple on which search done
@param mode PAGE_CUR_L, ...; NOTE that if the search is made using a
unique prefix of a record, mode should be PAGE_CUR_LE, not
PAGE_CUR_GE, as the latter may end up on the previous page of
the record!
@param latch_mode BTR_SEARCH_LEAF, ...; NOTE that if ahi_latch then we might
not acquire a cursor page latch, but assume that the
ahi_latch protects the record!
@param cursor memory buffer for persistent cursor
@param file file name
@param line line where called
@param mtr mtr
@return DB_SUCCESS on success or error code otherwise. */
UNIV_INLINE
dberr_t btr_pcur_open_with_no_init_func(dict_index_t *index,
const dtuple_t *tuple,
page_cur_mode_t mode, ulint latch_mode,
btr_pcur_t *cursor, const char *file,
unsigned line, mtr_t *mtr)
{
btr_cur_t* btr_cursor;
dberr_t err = DB_SUCCESS;
cursor->latch_mode = BTR_LATCH_MODE_WITHOUT_INTENTION(latch_mode);
cursor->search_mode = mode;
/* Search with the tree cursor */
btr_cursor = btr_pcur_get_btr_cur(cursor);
err = btr_cur_search_to_nth_level(
index, 0, tuple, mode, latch_mode, btr_cursor,
file, line, mtr);
cursor->pos_state = BTR_PCUR_IS_POSITIONED;
cursor->old_stored = false;
cursor->trx_if_known = NULL;
return err;
}
/*****************************************************************//**
Opens a persistent cursor at either end of an index. */
UNIV_INLINE
dberr_t
btr_pcur_open_at_index_side(
/*========================*/
bool from_left, /*!< in: true if open to the low end,
false if to the high end */
dict_index_t* index, /*!< in: index */
ulint latch_mode, /*!< in: latch mode */
btr_pcur_t* pcur, /*!< in/out: cursor */
bool init_pcur, /*!< in: whether to initialize pcur */
ulint level, /*!< in: level to search for
(0=leaf) */
mtr_t* mtr) /*!< in/out: mini-transaction */
{
dberr_t err = DB_SUCCESS;
pcur->latch_mode = BTR_LATCH_MODE_WITHOUT_FLAGS(latch_mode);
pcur->search_mode = from_left ? PAGE_CUR_G : PAGE_CUR_L;
if (init_pcur) {
btr_pcur_init(pcur);
}
err = btr_cur_open_at_index_side(
from_left, index, latch_mode,
btr_pcur_get_btr_cur(pcur), level, mtr);
pcur->pos_state = BTR_PCUR_IS_POSITIONED;
pcur->old_stored = false;
pcur->trx_if_known = NULL;
return (err);
}
/**********************************************************************//**
Positions a cursor at a randomly chosen position within a B-tree.
@return true if the index is available and we have put the cursor, false
if the index is unavailable */
UNIV_INLINE
bool
btr_pcur_open_at_rnd_pos_func(
/*==========================*/
dict_index_t* index, /*!< in: index */
ulint latch_mode, /*!< in: BTR_SEARCH_LEAF, ... */
btr_pcur_t* cursor, /*!< in/out: B-tree pcur */
const char* file, /*!< in: file name */
unsigned line, /*!< in: line where called */
mtr_t* mtr) /*!< in: mtr */
{
/* Initialize the cursor */
cursor->latch_mode = latch_mode;
cursor->search_mode = PAGE_CUR_G;
btr_pcur_init(cursor);
bool available;
available = btr_cur_open_at_rnd_pos_func(index, latch_mode,
btr_pcur_get_btr_cur(cursor),
file, line, mtr);
cursor->pos_state = BTR_PCUR_IS_POSITIONED;
cursor->old_stored = false;
cursor->trx_if_known = NULL;
return(available);
}
/**************************************************************//**
Frees the possible memory heap of a persistent cursor and sets the latch
mode of the persistent cursor to BTR_NO_LATCHES.
WARNING: this function does not release the latch on the page where the
cursor is currently positioned. The latch is acquired by the
"move to next/previous" family of functions. Since recursive shared locks
are not allowed, you must take care (if using the cursor in S-mode) to
manually release the latch by either calling
btr_leaf_page_release(btr_pcur_get_block(&pcur), pcur.latch_mode, mtr)
or by committing the mini-transaction right after btr_pcur_close().
A subsequent attempt to crawl the same page in the same mtr would cause
an assertion failure. */
UNIV_INLINE
void
btr_pcur_close(
/*===========*/
btr_pcur_t* cursor) /*!< in: persistent cursor */
{
ut_free(cursor->old_rec_buf);
if (cursor->btr_cur.rtr_info) {
rtr_clean_rtr_info(cursor->btr_cur.rtr_info, true);
cursor->btr_cur.rtr_info = NULL;
}
cursor->old_rec = NULL;
cursor->old_rec_buf = NULL;
cursor->btr_cur.page_cur.rec = NULL;
cursor->btr_cur.page_cur.block = NULL;
cursor->old_rec = NULL;
cursor->old_stored = false;
cursor->latch_mode = BTR_NO_LATCHES;
cursor->pos_state = BTR_PCUR_NOT_POSITIONED;
cursor->trx_if_known = NULL;
}
/*********************************************************//**
Moves the persistent cursor to the infimum record on the same page. */
UNIV_INLINE
void
btr_pcur_move_before_first_on_page(
/*===============================*/
btr_pcur_t* cursor) /*!< in/out: persistent cursor */
{
ut_ad(cursor->latch_mode != BTR_NO_LATCHES);
page_cur_set_before_first(btr_pcur_get_block(cursor),
btr_pcur_get_page_cur(cursor));
cursor->old_stored = false;
}
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