path: root/cpukit/include/rtems/score/percpu.h
diff options
authorSebastian Huber <>2020-02-26 10:02:37 +0100
committerSebastian Huber <>2020-02-28 07:50:19 +0100
commitfcb11510c6b38a7a1f4da7205acc5461a4e18214 (patch)
tree02f0c07dec4124f93eccdcdd45af06a9c9099fb7 /cpukit/include/rtems/score/percpu.h
parent2220a536e34261989042a381fab43e33ccc1fbb9 (diff)
score: Fix context switch extensions (SMP)
In uniprocessor and SMP configurations, the context switch extensions were called during _Thread_Do_dispatch(): void _Thread_Do_dispatch( Per_CPU_Control *cpu_self, ISR_Level level ) { Thread_Control *executing; executing = cpu_self->executing; ... do { Thread_Control *heir; heir = _Thread_Get_heir_and_make_it_executing( cpu_self ); ... _User_extensions_Thread_switch( executing, heir ); ... _Context_Switch( &executing->Registers, &heir->Registers ); ... } while ( cpu_self->dispatch_necessary ); ... } In uniprocessor configurations, this is fine and the context switch extensions are called for all thread switches except the very first thread switch to the initialization thread. However, in SMP configurations, the context switch may be invalidated and updated in the low-level _Context_Switch() routine. See: In case such an update happens, a thread will execute on the processor which was not seen in the previous call of the context switch extensions. This can confuse for example event record consumers which use events generated by a context switch extension. Fixing this is not straight forward. The context switch extensions call must move after the low-level context switch. The problem here is that we may end up in _Thread_Handler(). Adding the context switch extensions call to _Thread_Handler() covers now also the thread switch to the initialization thread. We also have to save the last executing thread (ancestor) of the processor. Registers or the stack cannot be used for this purpose. We have to add it to the per-processor information. Existing extensions may be affected, since now context switch extensions use the stack of the heir thread. The stack checker is affected by this. Calling the thread switch extensions in the low-level context switch is difficult since at this point an intermediate stack is used which is only large enough to enable servicing of interrupts. Update #3885.
Diffstat (limited to 'cpukit/include/rtems/score/percpu.h')
1 files changed, 7 insertions, 0 deletions
diff --git a/cpukit/include/rtems/score/percpu.h b/cpukit/include/rtems/score/percpu.h
index 7c95a9649a..31bc2b0bff 100644
--- a/cpukit/include/rtems/score/percpu.h
+++ b/cpukit/include/rtems/score/percpu.h
@@ -529,6 +529,13 @@ typedef struct Per_CPU_Control {
} Scheduler;
+ * @brief The ancestor of the executing thread.
+ *
+ * This member is used by _User_extensions_Thread_switch().
+ */
+ struct _Thread_Control *ancestor;
+ /**
* @brief Begin of the per-CPU data area.
* Contains items defined via PER_CPU_DATA_ITEM().