Disallow nesting of LITMUS^RT locks

Nesting of locks was never supported in LITMUS^RT since
the required analysis does not exist anyway. That is, as
defined in the literature, the protocols implemented
in LITMUS^RT have not been studied in conjunction with
nested critical sections.

In LITMUS^RT, attempting to nest locks could lead to
silent or not-so-silent bugs. This patch makes this
restriction explicit and returns EBUSY when a process
attempts to nest resources.

This is enforced on a protocol-by-protocol basis,
which means that adding protocols with support for
nesting in future versions is not affected by this
change.

Exception: PCP and SRP resources may be nested,
but not within global critical sections.

1 files changed, 5 insertions, 0 deletions

diff --git a/include/litmus/rt_param.h b/include/litmus/rt_param.h
index 4cd06dd32906..5487bdb11380 100644
--- a/include/litmus/rt_param.h
+++ b/include/litmus/rt_param.h
@@ -168,6 +168,11 @@ struct rt_param {
         unsigned int            priority_boosted:1;
         /* If so, when did this start? */
         lt_t                    boost_start_time;
+
+        /* How many LITMUS^RT locks does the task currently hold/wait for? */
+        unsigned int            num_locks_held;
+        /* How many PCP/SRP locks does the task currently hold/wait for? */
+        unsigned int            num_local_locks_held;
 #endif
 
         /* user controlled parameters */