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authorAnton Blanchard <anton@samba.org>2012-01-09 14:29:15 +0000
committerBenjamin Herrenschmidt <benh@kernel.crashing.org>2012-01-11 11:54:20 +1100
commita5ccfee05a439b803640e94584056204501db31c (patch)
tree2545bab092fe62924d5ccba8920c137b1e771ba6 /arch/powerpc
parent7b3480f8b701170c046e1ed362946f5f0d005e13 (diff)
powerpc: Fix RCU idle and hcall tracing
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 <anton@samba.org> Acked-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Diffstat (limited to 'arch/powerpc')
-rw-r--r--arch/powerpc/kernel/idle.c12
-rw-r--r--arch/powerpc/platforms/pseries/lpar.c14
2 files changed, 12 insertions, 14 deletions
diff --git a/arch/powerpc/kernel/idle.c b/arch/powerpc/kernel/idle.c
index 7c66ce13da89..0a48bf5db6c8 100644
--- a/arch/powerpc/kernel/idle.c
+++ b/arch/powerpc/kernel/idle.c
@@ -50,12 +50,6 @@ static int __init powersave_off(char *arg)
}
__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())
diff --git a/arch/powerpc/platforms/pseries/lpar.c b/arch/powerpc/platforms/pseries/lpar.c
index 948e0e3b3547..7bc73af6c7b9 100644
--- a/arch/powerpc/platforms/pseries/lpar.c
+++ b/arch/powerpc/platforms/pseries/lpar.c
@@ -546,6 +546,13 @@ void __trace_hcall_entry(unsigned long opcode, unsigned long *args)
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 opcode, unsigned long *args)
(*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, unsigned long retval,
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, unsigned long retval,
goto out;
(*depth)++;
- if (opcode == H_CEDE)
- rcu_idle_exit();
trace_hcall_exit(opcode, retval, retbuf);
preempt_enable();
(*depth)--;