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powerpc: Fix RCU idle and hcall tracing

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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 a7b152d534 (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>
This commit is contained in:
Anton Blanchard 2012-01-09 14:29:15 +00:00 committed by Benjamin Herrenschmidt
parent 7b3480f8b7
commit a5ccfee05a
2 changed files with 12 additions and 14 deletions
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12
arch/powerpc/kernel/idle.c
View File

@ -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())

14
arch/powerpc/platforms/pseries/lpar.c
View File

@ -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)--;