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MDEV-35828: Assertion fails in alloc_root() when memory causes it to call itself

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(Variant 2: use stack for buffers)
my_malloc_size_cb_func() has a call to thd->alloc() to produce an error message.
thd->alloc() calls alloc_root(), so one can end up with this stack trace:

  alloc_root()
  THD::alloc()
  my_malloc_size_cb_func()
  my_malloc()
  alloc_root()

where alloc_root() calls itself. This is a problem, as alloc_root() is not
reenterable.

Fixed this by switching my_malloc_size_cb_func() to use space on the stack
instead.
This commit is contained in:
Sergei Petrunia 2025-01-14 22:42:18 +02:00
parent d5a417b9d5
commit 196f38367a
3 changed files with 36 additions and 13 deletions
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13
mysql-test/main/errors.result
View file

@ -231,3 +231,16 @@ Error 1327 Undeclared variable: foo
Error 1305 PROCEDURE P1 does not exist
drop procedure P1;
# End of 10.4 tests
#
# MDEV-35828: Assertion fails in alloc_root() when memory causes it to call itself
#
SET
@tmp=@@max_session_mem_used,
max_session_mem_used=8192;
CREATE TEMPORARY TABLE t1 (a INT,b INT) ;
INSERT INTO t1 VALUES (1,1),(2,2);
SELECT * FROM (t1 AS t2 LEFT JOIN t1 AS t3 USING (a)),t1;
ERROR HY000: The MariaDB server is running with the --max-session-mem-used=8192 option so it cannot execute this statement
DROP TABLE t1;
SET max_session_mem_used=@tmp;
# End of 10.6 tests

18
mysql-test/main/errors.test
View file

@ -284,3 +284,21 @@ show warnings;
drop procedure P1;
-- echo # End of 10.4 tests
--echo #
--echo # MDEV-35828: Assertion fails in alloc_root() when memory causes it to call itself
--echo #
SET
@tmp=@@max_session_mem_used,
max_session_mem_used=8192;
CREATE TEMPORARY TABLE t1 (a INT,b INT) ;
INSERT INTO t1 VALUES (1,1),(2,2);
--error ER_OPTION_PREVENTS_STATEMENT
SELECT * FROM (t1 AS t2 LEFT JOIN t1 AS t3 USING (a)),t1;
DROP TABLE t1;
SET max_session_mem_used=@tmp;
--echo # End of 10.6 tests

10
sql/mysqld.cc
View file

@ -3666,22 +3666,14 @@ static void my_malloc_size_cb_func(long long size, my_bool is_thread_specific)
LOCK_thd_kill here (the limit will be enforced on the next allocation).
*/
if (!mysql_mutex_trylock(&thd->LOCK_thd_kill)) {
char buf[50], *buf2;
char buf[50], buf2[256];
thd->set_killed_no_mutex(KILL_QUERY);
my_snprintf(buf, sizeof(buf), "--max-session-mem-used=%llu",
thd->variables.max_mem_used);
if ((buf2= (char*) thd->alloc(256)))
{
my_snprintf(buf2, 256,
ER_THD(thd, ER_OPTION_PREVENTS_STATEMENT), buf);
thd->set_killed_no_mutex(KILL_QUERY,
ER_OPTION_PREVENTS_STATEMENT, buf2);
}
else
{
thd->set_killed_no_mutex(KILL_QUERY, ER_OPTION_PREVENTS_STATEMENT,
"--max-session-mem-used");
}
mysql_mutex_unlock(&thd->LOCK_thd_kill);
}
}