Bug #50912 Assertion `ticket->m_type >= mdl_request->type'

           failed on HANDLER + I_S

This assert was triggered when an I_S query tried to acquire a
metadata lock on a table which was already locked by a HANDLER
statement in the same connection.

First the HANDLER took a MDL_SHARED lock. Afterwards, the I_S query
requested a MDL_SHARED_HIGH_PRIO lock. The existing MDL_SHARED ticket
is found in find_ticket() since it satisfies 
ticket->has_stronger_or_equal_type(mdl_request->type) as MDL_SHARED
and MDL_SHARED_HIGH_PRIO have equal strengths, just different priority.

However, two asserts later check lock type strengths using relational
operators (>= and <=) rather than MDL_ticket::has_stronger_or_equal_type().
These asserts are triggered since MDL_SHARED >= MDL_SHARED_HIGH_PRIORITY
is false (mapped to 1 and 2 respectively).

This patch updates the asserts to use MDL_ticket::has_stronger_or_equal_type()
rather than relational operators to check lock type strength.

Test case added to include/handler.inc.

1 files changed, 2 insertions, 2 deletions

diff --git a/sql/mdl.cc b/sql/mdl.cc
index 2470ce5b4b7..54931f89e40 100644
--- a/sql/mdl.cc
+++ b/sql/mdl.cc
@@ -1261,7 +1261,7 @@ MDL_context::try_acquire_lock(MDL_request *mdl_request)
   if ((ticket= find_ticket(mdl_request, &is_transactional)))
   {
     DBUG_ASSERT(ticket->m_lock);
-    DBUG_ASSERT(ticket->m_type >= mdl_request->type);
+    DBUG_ASSERT(ticket->has_stronger_or_equal_type(mdl_request->type));
     /*
       If the request is for a transactional lock, and we found
       a transactional lock, just reuse the found ticket.
@@ -1349,7 +1349,7 @@ MDL_context::clone_ticket(MDL_request *mdl_request)
     return TRUE;
 
   /* clone() is not supposed to be used to get a stronger lock. */
-  DBUG_ASSERT(ticket->m_type <= mdl_request->ticket->m_type);
+  DBUG_ASSERT(mdl_request->ticket->has_stronger_or_equal_type(ticket->m_type));
 
   ticket->m_lock= mdl_request->ticket->m_lock;
   mdl_request->ticket= ticket;