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Re: bzr commit into MySQL/Maria:mysql-maria branch (monty:2725) Bug#40711
>>>>> "Guilhem" == Guilhem Bichot <guilhem@xxxxxxx> writes:
>> +++ b/storage/maria/ma_close.c 2009-02-01 07:29:56 +0000
>> @@ -155,7 +155,7 @@ int maria_close(register MARIA_HA *info)
>> MARIA_STATE_HISTORY_CLOSED *history;
>> Here we ignore the unlikely case that we don't have memory to
>> - store the case. In the worst case what happens is that any transaction
>> + store the state. In the worst case what happens is that any transaction
>> that tries to access this table will get a wrong status information.
>> if ((history= (MARIA_STATE_HISTORY_CLOSED *)
>> @@ -166,6 +166,8 @@ int maria_close(register MARIA_HA *info)
>> if (my_hash_insert(&maria_stored_state, (uchar*) history))
>> my_free(history, MYF(0));
>> + /* Marker for concurrent checkpoint */
>> + share->state_history= 0;
Guilhem> So, what was the scenario?
Guilhem> I imagined this one: Thread1 has just closed the table, but Thread2 had
Guilhem> started a checkpoint, so Thread1 leaves the share in existence; Thread2
Guilhem> looks at share->state_history, but why would that point to freed memory?
Guilhem> Is it because there is a Thread3 which did this freeing?
No, the problem happens with only two threads.
T1 one goes into the above code and creates a history entry that
points to share->state_history.
In checkpoint thread we will then execute the following code:
Which uses share->state_history entry and may even free it.
If free happens, we are likely to get a crash as history entry now
points to freed memory.