- Restarting mysqld with --expire-log-days=1 triggers 'log_in_use()' to be called while current_thd is NULL.
 - Check current_thd before calling DEBUG_SYNC() to avoid passing NULL pointer to DEBUG_SYNC()
 - Wrap debug code construct inside #ifndef DBUG_OFF like in other parts of the file

Normally, SET SESSION SQL_LOG_BIN is used by DBAs to run a
non-conflicting command locally only, ensuring it does not
get replicated.
Setting GLOBAL SQL_LOG_BIN would not require all sessions to
disconnect. When SQL_LOG_BIN is changed globally, it does not
immediately take effect for any sessions. It takes effect by
becoming the session-level default inherited at the start of
each new session, and this setting is kept and cached for the
duration of that session. Setting it intentionally is unlikely
to have a useful effect under any circumstance; setting it
unintentionally, such as while intending to use SET [SESSION]
is potentially disastrous. Accidentally using SET GLOBAL
SQL_LOG_BIN will not show an immediate effect to the user,
instead not having the desired session-level effect, and thus
causing other potential problems with local-only maintenance
being binlogged and executed on slaves; And transactions from
new sessions (after SQL_LOG_BIN is changed globally) are not
binlogged and replicated, which would result in irrecoverable
or difficult data loss.
This is the regular GLOBAL variables way to work, but in
replication context it does not look right on a working server
(with connected sessions) 'set global sql_log_bin' and none of
that connections is affected. Unexperienced DBA after noticing
that the command did "nothing" will change the session var and
most probably won't unset the global var, causing new sessions
to not be binlog.
Setting GLOBAL SQL_LOG_BIN allows DBA to stop binlogging on all
new sessions, which can be used to make a server "replication
read-only" without restarting the server. But this has such big
requirements, stop all existing connections, that it is more
likely to make a mess, it is too risky to allow the GLOBAL variable.

The statement 'SET GLOBAL SQL_LOG_BIN=N' will produce an error
in 5.5, 5.6 and 5.7. Reading the GLOBAL SQL_LOG_BIN will produce
a deprecation warning in 5.7.

FROM A FUNCTION

Scenario:

In a stored procedure, CREATE TABLE statement is not allowed.  But an
exception is provided for CREATE TEMPORARY TABLE.  We can create a temporary
table in a stored procedure.

Let there be two stored functions f1 and f2 and two stored procedures p1 and
p2.  Their properties are as follows:

. stored function f1() calls stored procedure p1().
. stored function f2() calls stored procedure p2().
. stored procedure p1() creates temporary table t1.
. stored procedure p2() does DML on t1.

Consider the following situation:

1.  Autocommit mode is on. 
2.  select f1()
3.  select f2()

Step 2:  In this step, t1 would be created via p1().  A table level transaction
lock would have been taken.  The ::external_lock() would not have been called
on this table.  At the end of step 2, because of autocommit mode on, this table
level lock will be released.

Step 3:  When we execute DML on table t1 via p2() we have two problems:

Problem 1:

The function ha_innobase::external_lock() would have been called but since
it is a select query no table level locks would have been taken.  Hence the
following assert will fail:

ut_ad(lock_table_has(thr_get_trx(thr), index->table, LOCK_IX));

Solution:

The solution would be to identify this situation and take a table level lock
and use the proper lock type prebuilt->select_lock_type = LOCK_X for DML
operations.

Problem 2:

Another problem is that in step 3, ha_innobase::open() is never called on
the table t1.  

Solution:

The solution would be to identify this situation and call re-init the handler
of table t1.

rb#6429 approved by Krunal.

Problem:

Creation of a table fails when innodb_strict_mode is enabled, but the same
table is created without any warning when innodb_strict_mode is enabled.

Solution:

If creation of a table fails with an error when innodb_strict_mode is
enabled, it must issue a warning when innodb_strict_mode is disabled.

rb#6723 approved by Krunal.

                AND IS_USED_LOCK().

Analysis:
-----------
In functions Item_func_is_free_lock::val_int() and 
Item_func_is_used_lock::val_int(), for the specified user lock
name, pointer to its "User_level_lock" object is obtained from hash
"hash_user_locks". Mutex "LOCK_user_locks" is acquired for this
and released immediately. And we are accessing members of
User_level_lock after releasing the mutex. If same user lock is
deleted(released) from concurrent thread then accessing members
results in invalid(freed) memory access issue.

Deleting of user lock is also protected from the mutex
"LOCK_user_locks". Since this mutex is released in "val_int" 
functions mentioned above, delete operation proceeds while concurrent
thread tries to access its members.

With the test case, valgrind reports invalid read issues in val_int
functions.

Fix:
-----------
To fix this issue, in "val_int" function of classes
"Item_func_is_free_lock" and "Item_func_is_used_lock", now releasing
mutex "LOCK_user_locks" after accessing User_level_lock members.

No commit message

               CHECK.

Analysis:
----------
Issue here is, while creating or altering the InnoDB table,
if the foreign key defined on the table references a parent
table on which the user has no access privileges then the
table is created without reporting any error. 

Currently the privilege level REFERENCES_ACL is unused
and is not used for access evaluation while creating the
table with a foreign key constraint or adding the foreign
key constraint to a table. But when no privileges are granted
to user then also access evaluation on parent table is ignored.

Fix:
---------
For DMLs, irrelevant of the fact, support does not want any
changes to avoid permission checks on every operation.

So, as a fix, added a function "check_fk_parent_table_access" 
to check whether any of the SELECT_ACL, INSERT_ACL, UDPATE_ACL,
DELETE_ACL or REFERENCE_ACL privileges are granted for user
at table level. If none of them is granted then error is reported.
This function is called during the table creation and alter 
operation. 

      
      Problem: A corrupted header length in FORMAT_DESCRIPTION_LOG_EVENT
      can cause server to crash.
      Analysis: FORMAT_DESCRIPTION_EVENT will be considered invalid if
      header len is too small (i.e. below OLD_HEADER_LEN).
      
      Format_description_log_event:: Format_description_log_event(...)
      {
        ...
        if ((common_header_len=buf[ST_COMMON_HEADER_LEN_OFFSET]) < OLD_HEADER_LEN)
          DBUG_VOID_RETURN; /* sanity check */
        ...
        post_header_len= my_memdup(...)
      }
      
      In that case Format_description_log_event constructor will return early,
      without allocating any memory for post_header_len. Thence this variable is
      left uninitialized and making server to crash when server is trying
      to free the uninitialized value.
      
      Fix: When Format_description_log_event constructor returns early, assign
      NULL to post_header_len.

No commit message

Problem:

We maintain two rb trees in each dict_table_t.  The foreign_rbt must be in
sync with foreign_list.  The referenced_rbt must be in sync with
referenced_list. There is one function which checks this consistency and it
failed, resulting in an assert failure.

The root cause of the problem was identified that the search order was 
lost in the referenced_rbt.  This is because while renaming the table,
we didn't not refresh this referenced_rbt.

Solution:

When a foreign key is renamed, we must delete and re-insert into both
foreign_rbt and referenced_rbt.  

rb#6412 approved by Jimmy.

               LIES ABOUT SUITE_LEN_
               and
Bug#19355577 : YASSL PRE-AUTH BUFFER OVERFLOW WHEN CLIENT
               LIES ABOUT COMP_LEN_

Description : Updating yaSSL to version 2.3.4.

Several string functions have optimizations for constant
sub-expressions which lead to setting max_length == 0.

For subqueries, where we need a temporary table to holde the result,
we need to ensure that we use a VARCHAR(0) column rather than a
CHAR(0) column when such expressions take part in grouping.
With CHAR(0) end_update() may write garbage into the next field.

                COLLATIONS ARE USED.

ISSUE :
-------
Code points of HALF WIDTH KATAKANA in SJIS/CP932 range from
A1 to DF. In function my_wildcmp_mb_bin_impl while comparing
such single byte code points, there is a code which compares
signed character with unsigned character. Because of this,
comparisons of two same code points representing a HALF
WIDTH KATAKANA character always fails.

Solution:
---------
A code point of HALF WIDTH KATAKANA at-least need 8 bits.
Promoting the variable from uchar to int will fix the issue.

- Reverted version variable 

Follow-up patch. Removed unwanted code.

Description: mysql_upgrade fails with below error, 
when there are duplicate entries(like 'root'@'LOCALHOST'
and 'root'@'localhost') in mysql.user table.
ERROR 1062 (23000) at line 1140: Duplicate entry 'localhost-root' for key 'PRIMARY'
FATAL ERROR: Upgrade failed

Analysis: As part of the bug 12917151 fix we are 
making all the hostnames as lower case hostnames.
So, this has been done by mysql_upgrade.
In case of above mentioned duplicate entries 
mysql_upgrade tries to change hostname to lowercase.
Since there is already 'root'@'localhost' exists.
it is failing with "duplicate entry" error.

Fix: Since its a valid error failure. We are 
making the error more verbose. So, that user will
delete the duplicate errors manually.
Along with existing error we are printing below
error as well.
ERROR 1644 (45000) at line 1153: Multiple accounts exist for @user_name, @host_name that differ only in Host lettercase; remove all except one of them