cpuidle: fix fallback mechanism for suspend to idle in absence of enter_freeze

Message ID 1453375169-14768-1-git-send-email-sudeep.holla@arm.com
State New
Headers show

Commit Message

Sudeep Holla Jan. 21, 2016, 11:19 a.m.
Commit 51164251f5c3 ("sched / idle: Drop default_idle_call() fallback
from call_cpuidle()") made find_deepest_state() return non-negative
value and check all the states with index > 0. Also a result,
find_deepest_state() returns 0 even when enter_freeze callbacks are not
implemented and enter_freeze_proper is called which ends up crashing
the kernel.

This patch updates the check for index > 0 in cpuidle_enter_freeze and
cpuidle_idle_call(when idle_should_freeze is true) to restore the
suspend-to-idle functionality in absence of enter_freeze callback.

Fixes: 51164251f5c3 ("sched / idle: Drop default_idle_call() fallback from call_cpuidle()")
Cc: "Rafael J. Wysocki" <rjw@rjwysocki.net>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Sudeep Holla <sudeep.holla@arm.com>

---
 drivers/cpuidle/cpuidle.c | 2 +-
 kernel/sched/idle.c       | 2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)

Hi Rafael,

I assume you prefer to retain find_deepest_state return non-negative
values, so I took this approach for fixing the bug. Do you think we
need to support enter_freeze_proper for index 0 ?

Regards,
Sudeep

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Comments

Sudeep Holla Jan. 22, 2016, 9:20 a.m. | #1
On 22/01/16 01:15, Rafael J. Wysocki wrote:
> On Thursday, January 21, 2016 11:19:29 AM Sudeep Holla wrote:

>> Commit 51164251f5c3 ("sched / idle: Drop default_idle_call() fallback

>> from call_cpuidle()") made find_deepest_state() return non-negative

>> value and check all the states with index > 0. Also a result,

>> find_deepest_state() returns 0 even when enter_freeze callbacks are not

>> implemented and enter_freeze_proper is called which ends up crashing

>> the kernel.

>>

>> This patch updates the check for index > 0 in cpuidle_enter_freeze and

>> cpuidle_idle_call(when idle_should_freeze is true) to restore the

>> suspend-to-idle functionality in absence of enter_freeze callback.

>>

>> Fixes: 51164251f5c3 ("sched / idle: Drop default_idle_call() fallback from call_cpuidle()")

>> Cc: "Rafael J. Wysocki" <rjw@rjwysocki.net>

>> Cc: Ingo Molnar <mingo@redhat.com>

>> Cc: Peter Zijlstra <peterz@infradead.org>

>> Signed-off-by: Sudeep Holla <sudeep.holla@arm.com>

>> ---

>>   drivers/cpuidle/cpuidle.c | 2 +-

>>   kernel/sched/idle.c       | 2 +-

>>   2 files changed, 2 insertions(+), 2 deletions(-)

>>

>> Hi Rafael,

>

> Hi,

>

> Sorry for the breakage.

>


Sorry that I missed to test suspend-to-idle before it got merged.

>> I assume you prefer to retain find_deepest_state return non-negative

>> values, so I took this approach for fixing the bug. Do you think we

>> need to support enter_freeze_proper for index 0 ?

>

> Zero is a special case on x86, so supporting enter_freeze_proper() for it

> is not necessary.

>


Even on ARM, 0 is used for WFI only, which will not be used for freeze.

> If you think we can also make 0 a special case on ARM, the others should

> not object to that either.

>


Makes sense and since it's already reserved for WFI on ARM, it should be
fine. If there are no objections, can you pick up this fix ?

-- 
Regards,
Sudeep
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Patch

diff --git a/drivers/cpuidle/cpuidle.c b/drivers/cpuidle/cpuidle.c
index 046423b0c5ca..f996efc56605 100644
--- a/drivers/cpuidle/cpuidle.c
+++ b/drivers/cpuidle/cpuidle.c
@@ -153,7 +153,7 @@  int cpuidle_enter_freeze(struct cpuidle_driver *drv, struct cpuidle_device *dev)
 	 * be frozen safely.
 	 */
 	index = find_deepest_state(drv, dev, UINT_MAX, 0, true);
-	if (index >= 0)
+	if (index > 0)
 		enter_freeze_proper(drv, dev, index);

 	return index;
diff --git a/kernel/sched/idle.c b/kernel/sched/idle.c
index de0e786b2667..544a7133cbd1 100644
--- a/kernel/sched/idle.c
+++ b/kernel/sched/idle.c
@@ -162,7 +162,7 @@  static void cpuidle_idle_call(void)
 	 */
 	if (idle_should_freeze()) {
 		entered_state = cpuidle_enter_freeze(drv, dev);
-		if (entered_state >= 0) {
+		if (entered_state > 0) {
 			local_irq_enable();
 			goto exit_idle;
 		}