[PATCH][RFC] cpufreq: Avoid warning during resume by return EAGAIN if cpufreq is unavailable

Previously we saw warning during resume on some platforms,
which use acpi-cpufreq:

smpboot: Booting Node 0 Processor 3 APIC 0x5
cache: parent cpu3 should not be sleeping
CPU3 is up
ACPI: Waking up from system sleep state S3
WARNING: CPU: 0 PID: 12546 at drivers/cpufreq/cpufreq.c:2173
Call Trace:
[<ffffffff81311d95>] dump_stack+0x5c/0x77
[<ffffffff8107aef4>] __warn+0xc4/0xe0
[<ffffffff8148c13e>] cpufreq_update_policy+0xfe/0x150
[<ffffffff8148c190>] cpufreq_update_policy+0x150/0x150
[<ffffffffc03e42ef>] acpi_processor_notify+0x51/0xdc [processor]
[<ffffffff813b0d24>] acpi_ev_notify_dispatch+0x3c/0x55
[<ffffffff81399613>] acpi_os_execute_deferred+0x10/0x1a
[<ffffffff81093ffb>] process_one_work+0x14b/0x400
[<ffffffff81094aa5>] worker_thread+0x65/0x4a0
[<ffffffff81094a40>] rescuer_thread+0x340/0x340
[<ffffffff81099dbf>] kthread+0xdf/0x100
[<ffffffff815c7ee2>] ret_from_fork+0x22/0x40
[<ffffffff81099ce0>] kthread_park+0x50/0x50

This is because this platforms tries to notify
the processor to reevaluate the _PPC object in _WAK,
however at that time the cpufreq driver's resume has
not been invoked yet, thus cpufreq_update_current_freq
returns zero because of cpufreq_suspended = true, which
caused the warning.

Actually it should be unnecessary to care the update request
at that moment, so remove the warning and change the return
value to -EAGAIN for invokers.

Reported-and-tested-by: BzukTuk <redacted>
Signed-off-by: Chen Yu <yu.c.chen@intel.com>
---
 drivers/cpufreq/cpufreq.c | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c
index 9009295..67a3aa1 100644
--- a/drivers/cpufreq/cpufreq.c
+++ b/drivers/cpufreq/cpufreq.c

@@ -2262,8 +2262,11 @@ int cpufreq_update_policy(unsigned int cpu)
 	 */
 	if (cpufreq_driver->get && !cpufreq_driver->setpolicy) {
 		new_policy.cur = cpufreq_update_current_freq(policy);
-		if (WARN_ON(!new_policy.cur)) {
-			ret = -EIO;
+		if (!new_policy.cur) {
+			if (WARN_ON(!cpufreq_suspended))
+				ret = -EIO;
+			else
+				ret = -EAGAIN;
 			goto unlock;
 		}
 	}

-- 
2.7.4

On Sunday, June 26, 2016 12:28:48 AM Chen Yu wrote:

If we know that cpufreq is suspended, there's no reason to call
cpufreq_update_current_freq() at all here.

Moreover, cpufreq_update_current_freq() has only two callers and the other
one already checks cpufreq_suspended before invoking it, so what about the
patch below instead?

---
 drivers/cpufreq/cpufreq.c |    7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

Index: linux-pm/drivers/cpufreq/cpufreq.c
===================================================================

--- linux-pm.orig/drivers/cpufreq/cpufreq.c
+++ linux-pm/drivers/cpufreq/cpufreq.c

@@ -1544,9 +1544,6 @@ static unsigned int cpufreq_update_curre
 {
 	unsigned int new_freq;
 
-	if (cpufreq_suspended)
-		return 0;
-
 	new_freq = cpufreq_driver->get(policy->cpu);
 	if (!new_freq)
 		return 0;

@@ -2280,6 +2277,10 @@ int cpufreq_update_policy(unsigned int c
 	 * -> ask driver for current freq and notify governors about a change
 	 */
 	if (cpufreq_driver->get && !cpufreq_driver->setpolicy) {
+		if (cpufreq_suspended) {
+			ret = -EAGAIN;
+			goto unlock;
+		}
 		new_policy.cur = cpufreq_update_current_freq(policy);
 		if (WARN_ON(!new_policy.cur)) {
 			ret = -EIO;

On 27-06-16, 03:12, Rafael J. Wysocki wrote:

Acked-by: Viresh Kumar <viresh.kumar@linaro.org>
-- 
viresh

On Monday, June 27, 2016 12:50:27 PM Viresh Kumar wrote:

On 27-06-16, 03:12, Rafael J. Wysocki wrote:

quoted

---
 drivers/cpufreq/cpufreq.c |    7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

Index: linux-pm/drivers/cpufreq/cpufreq.c
===================================================================

--- linux-pm.orig/drivers/cpufreq/cpufreq.c
+++ linux-pm/drivers/cpufreq/cpufreq.c

@@ -1544,9 +1544,6 @@ static unsigned int cpufreq_update_curre
 {
 	unsigned int new_freq;
 
-	if (cpufreq_suspended)
-		return 0;
-
 	new_freq = cpufreq_driver->get(policy->cpu);
 	if (!new_freq)
 		return 0;

@@ -2280,6 +2277,10 @@ int cpufreq_update_policy(unsigned int c
 	 * -> ask driver for current freq and notify governors about a change
 	 */
 	if (cpufreq_driver->get && !cpufreq_driver->setpolicy) {
+		if (cpufreq_suspended) {
+			ret = -EAGAIN;
+			goto unlock;
+		}
 		new_policy.cur = cpufreq_update_current_freq(policy);
 		if (WARN_ON(!new_policy.cur)) {
 			ret = -EIO;

Acked-by: Viresh Kumar <viresh.kumar@linaro.org>

Thanks, but this needs to go in in two pieces, because cpufreq_start_governor()
in the mainline doesn't check cpufreq_suspended (the linux-next version of it
does that).

So the second part of the patch is needed in the mainline/stable to get rid
of false-positive WARN_ON()s and the first one can go in on top of the
previous linux-next changes.

Thanks,
Rafael