Tracepoints should not be called inside an rcu_idle_enter/rcu_idle_exit
region. Since pSeries calls H_CEDE in the idle loop, we were violating
this rule.
commit a7b152d5342c (powerpc: Tell RCU about idle after hcall tracing)
tried to work around it by delaying the rcu_idle_enter until after we
called the hcall tracepoint, but there are a number of issues with it.
The hcall tracepoint trampoline code is called conditionally when the
tracepoint is enabled. If the tracepoint is not enabled we never call
rcu_idle_enter. The idle_uses_rcu check was also done at compile time
which breaks multiplatform builds.
The simple fix is to avoid tracing H_CEDE and rely on other tracepoints
and the hypervisor dispatch trace log to work out if we called H_CEDE.
This fixes a hang during boot on pSeries.
Signed-off-by: Anton Blanchard <an...@samba.org>
---
Index: linux-build/arch/powerpc/kernel/idle.c
===================================================================
--- linux-build.orig/arch/powerpc/kernel/idle.c 2012-01-10 11:07:22.091615183
+1100
+++ linux-build/arch/powerpc/kernel/idle.c 2012-01-10 11:07:57.172264229
+1100
@@ -50,12 +50,6 @@ static int __init powersave_off(char *ar
}
__setup("powersave=off", powersave_off);
-#if defined(CONFIG_PPC_PSERIES) && defined(CONFIG_TRACEPOINTS)
-static const bool idle_uses_rcu = 1;
-#else
-static const bool idle_uses_rcu;
-#endif
-
/*
* The body of the idle task.
*/
@@ -67,8 +61,7 @@ void cpu_idle(void)
set_thread_flag(TIF_POLLING_NRFLAG);
while (1) {
tick_nohz_idle_enter();
- if (!idle_uses_rcu)
- rcu_idle_enter();
+ rcu_idle_enter();
while (!need_resched() && !cpu_should_die()) {
ppc64_runlatch_off();
@@ -106,8 +99,7 @@ void cpu_idle(void)
HMT_medium();
ppc64_runlatch_on();
- if (!idle_uses_rcu)
- rcu_idle_exit();
+ rcu_idle_exit();
tick_nohz_idle_exit();
preempt_enable_no_resched();
if (cpu_should_die())
Index: linux-build/arch/powerpc/platforms/pseries/lpar.c
===================================================================
--- linux-build.orig/arch/powerpc/platforms/pseries/lpar.c 2012-01-10
11:07:22.079614961 +1100
+++ linux-build/arch/powerpc/platforms/pseries/lpar.c 2012-01-10
11:16:55.710226236 +1100
@@ -546,6 +546,13 @@ void __trace_hcall_entry(unsigned long o
unsigned long flags;
unsigned int *depth;
+ /*
+ * We cannot call tracepoints inside RCU idle regions which
+ * means we must not trace H_CEDE.
+ */
+ if (opcode == H_CEDE)
+ return;
+
local_irq_save(flags);
depth = &__get_cpu_var(hcall_trace_depth);
@@ -556,8 +563,6 @@ void __trace_hcall_entry(unsigned long o
(*depth)++;
preempt_disable();
trace_hcall_entry(opcode, args);
- if (opcode == H_CEDE)
- rcu_idle_enter();
(*depth)--;
out:
@@ -570,6 +575,9 @@ void __trace_hcall_exit(long opcode, uns
unsigned long flags;
unsigned int *depth;
+ if (opcode == H_CEDE)
+ return;
+
local_irq_save(flags);
depth = &__get_cpu_var(hcall_trace_depth);
@@ -578,8 +586,6 @@ void __trace_hcall_exit(long opcode, uns
goto out;
(*depth)++;
- if (opcode == H_CEDE)
- rcu_idle_exit();
trace_hcall_exit(opcode, retval, retbuf);
preempt_enable();
(*depth)--;
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