linux.git/drivers/cpufreq, branch v3.12-rc2

cpufreq: return EEXIST instead of EBUSY for second registering

2013-09-19T22:37:10+00:00

On systems that support intel_pstate, acpi_cpufreq fails to load, and
udev keeps trying until trace gets filled up and kernel crashes.

The root cause is driver return ret from cpufreq_register_driver(),
because when some other driver takes over before, it will return
EBUSY and then udev will keep trying ...

cpufreq_register_driver() should return EEXIST instead so that the
system can boot without appending intel_pstate=disable and still use
intel_pstate.

Signed-off-by: Yinghai Lu 
Acked-by: Viresh Kumar 
Signed-off-by: Rafael J. Wysocki

cpufreq: imx6q-cpufreq: assign cpu_dev correctly to cpu0 device

2013-09-19T01:53:43+00:00

Commit cdc58d602d2e657602a90c190cbf745886c95977 "cpufreq: imx6q-cpufreq:
remove device tree parsing for cpu nodes" assumed the pdev->dev is set to
cpu0 device in the platform code. But it actually points to the virtual
cpufreq-cpu0 platform device which is not present in the device tree.
Most of the information needed by cpufreq is stored in cpu0 DT node.
So cpu_dev must point to cpu0 device.

This patch fixes the wrong assignment to cpu_dev.

Reported-by: Guennadi Liakhovetski 
Tested-by: Shawn Guo 
Signed-off-by: Sudeep KarkadaNagesha 
Signed-off-by: Rafael J. Wysocki

cpufreq: cpufreq-cpu0: assign cpu_dev correctly to cpu0 device

2013-09-19T01:53:43+00:00

Commit f837a9b5ab05c52a07108c6f09ca66f2e0aee757 "cpufreq: cpufreq-cpu0:
remove device tree parsing for cpu nodes" assumed the pdev->dev is set to
cpu0 device in the platform code. But it actually points to the virtual
cpufreq-cpu0 platform device which is not present in the device tree.
Most of the information needed by cpufreq is stored in cpu0 DT node.
So cpu_dev must point to cpu0 device.

This patch fixes the wrong assignment to cpu_dev.

Reported-and-tested-by: Guennadi Liakhovetski 
Cc: Shawn Guo 
Signed-off-by: Sudeep KarkadaNagesha 
Signed-off-by: Rafael J. Wysocki

cpufreq: unlock correct rwsem while updating policy->cpu

2013-09-17T22:01:52+00:00

Current code looks like this:

        WARN_ON(lock_policy_rwsem_write(cpu));
        update_policy_cpu(policy, new_cpu);
        unlock_policy_rwsem_write(cpu);

{lock|unlock}_policy_rwsem_write(cpu) takes/releases policy->cpu's rwsem.
Because cpu is changing with the call to update_policy_cpu(), the
unlock_policy_rwsem_write() will release the incorrect lock.

The right solution would be to release the same lock as was taken earlier. Also
update_policy_cpu() was also called from cpufreq_add_dev() without any locks and
so its better if we move this locking to inside update_policy_cpu().

This patch fixes a regression introduced in 3.12 by commit f9ba680d23
(cpufreq: Extract the handover of policy cpu to a helper function).

Reported-and-tested-by: Jon Medhurst
Signed-off-by: Viresh Kumar 
Signed-off-by: Rafael J. Wysocki

cpufreq: Clear policy->cpus bits in __cpufreq_remove_dev_finish()

2013-09-17T22:01:27+00:00

This broke after a recent change "cedb70a cpufreq: Split __cpufreq_remove_dev()
into two parts" from Srivatsa.

Consider a scenario where we have two CPUs in a policy (0 & 1) and we are
removing CPU 1. On the call to __cpufreq_remove_dev_prepare() we have cleared 1
from policy->cpus and now on a call to __cpufreq_remove_dev_finish() we read
cpumask_weight of policy->cpus, which will come as 1 and this code will behave
as if we are removing the last CPU from policy :)

Fix it by clearing the CPU mask in __cpufreq_remove_dev_finish() instead of
__cpufreq_remove_dev_prepare().

Tested-by: Stephen Warren 
Reviewed-by: Srivatsa S. Bhat 
Signed-off-by: Viresh Kumar 
Signed-off-by: Rafael J. Wysocki

Merge branch 'pm-cpufreq'

2013-09-12T11:04:11+00:00

* pm-cpufreq:
  cpufreq: Acquire the lock in cpufreq_policy_restore() for reading
  cpufreq: Prevent problems in update_policy_cpu() if last_cpu == new_cpu
  cpufreq: Restructure if/else block to avoid unintended behavior
  cpufreq: Fix crash in cpufreq-stats during suspend/resume

cpufreq: Acquire the lock in cpufreq_policy_restore() for reading

2013-09-11T21:30:03+00:00

In cpufreq_policy_restore() before system suspend policy is read from
percpu's cpufreq_cpu_data_fallback.  It's a read operation rather
than a write one, so take the lock for reading in there.

Signed-off-by: Lan Tianyu 
Reviewed-by: Srivatsa S. Bhat 
Acked-by: Viresh Kumar 
Signed-off-by: Rafael J. Wysocki

cpufreq: Prevent problems in update_policy_cpu() if last_cpu == new_cpu

2013-09-11T21:29:57+00:00

If update_policy_cpu() is invoked with the existing policy->cpu itself
as the new-cpu parameter, then a lot of things can go terribly wrong.

In its present form, update_policy_cpu() always assumes that the new-cpu
is different from policy->cpu and invokes other functions to perform their
respective updates. And those functions implement the actual update like
this:

per_cpu(..., new_cpu) = per_cpu(..., last_cpu);
per_cpu(..., last_cpu) = NULL;

Thus, when new_cpu == last_cpu, the final NULL assignment makes the per-cpu
references vanish into thin air! (memory leak). From there, it leads to more
problems: cpufreq_stats_create_table() now doesn't find the per-cpu reference
and hence tries to create a new sysfs-group; but sysfs already had created
the group earlier, so it complains that it cannot create a duplicate filename.
In short, the repercussions of a rather innocuous invocation of
update_policy_cpu() can turn out to be pretty nasty.

Ideally update_policy_cpu() should handle this situation (new == last)
gracefully, and not lead to such severe problems. So fix it by adding an
appropriate check.

Signed-off-by: Srivatsa S. Bhat 
Tested-by: Stephen Warren 
Signed-off-by: Rafael J. Wysocki

cpufreq: Restructure if/else block to avoid unintended behavior

2013-09-11T21:29:57+00:00

In __cpufreq_remove_dev_prepare(), the code which decides whether to remove
the sysfs link or nominate a new policy cpu, is governed by an if/else block
with a rather complex set of conditionals. Worse, they harbor a subtlety
which leads to certain unintended behavior.

The code looks like this:

        if (cpu != policy->cpu && !frozen) {
                sysfs_remove_link(&dev->kobj, "cpufreq");
        } else if (cpus > 1) {
		new_cpu = cpufreq_nominate_new_policy_cpu(...);
		...
		update_policy_cpu(..., new_cpu);
	}

The original intention was:
If the CPU going offline is not policy->cpu, just remove the link.
On the other hand, if the CPU going offline is the policy->cpu itself,
handover the policy->cpu job to some other surviving CPU in that policy.

But because the 'if' condition also includes the 'frozen' check, now there
are *two* possibilities by which we can enter the 'else' block:

1. cpu == policy->cpu (intended)
2. cpu != policy->cpu && frozen (unintended)

Due to the second (unintended) scenario, we end up spuriously nominating
a CPU as the policy->cpu, even when the existing policy->cpu is alive and
well. This can cause problems further down the line, especially when we end
up nominating the same policy->cpu as the new one (ie., old == new),
because it totally confuses update_policy_cpu().

To avoid this mess, restructure the if/else block to only do what was
originally intended, and thus prevent any unwelcome surprises.

Signed-off-by: Srivatsa S. Bhat 
Tested-by: Stephen Warren 
Signed-off-by: Rafael J. Wysocki

cpufreq: Fix crash in cpufreq-stats during suspend/resume

2013-09-11T21:29:57+00:00

Stephen Warren reported that the cpufreq-stats code hits a NULL pointer
dereference during the second attempt to suspend a system. He also
pin-pointed the problem to commit 5302c3f "cpufreq: Perform light-weight
init/teardown during suspend/resume".

That commit actually ensured that the cpufreq-stats table and the
cpufreq-stats sysfs entries are *not* torn down (ie., not freed) during
suspend/resume, which makes it all the more surprising. However, it turns
out that the root-cause is not that we access an already freed memory, but
that the reference to the allocated memory gets moved around and we lose
track of that during resume, leading to the reported crash in a subsequent
suspend attempt.

In the suspend path, during CPU offline, the value of policy->cpu is updated
by choosing one of the surviving CPUs in that policy, as long as there is
atleast one CPU in that policy. And cpufreq_stats_update_policy_cpu() is
invoked to update the reference to the stats structure by assigning it to
the new CPU. However, in the resume path, during CPU online, we end up
assigning a fresh CPU as the policy->cpu, without letting cpufreq-stats
know about this. Thus the reference to the stats structure remains
(incorrectly) associated with the old CPU. So, in a subsequent suspend attempt,
during CPU offline, we end up accessing an incorrect location to get the
stats structure, which eventually leads to the NULL pointer dereference.

Fix this by letting cpufreq-stats know about the update of the policy->cpu
during CPU online in the resume path. (Also, move the update_policy_cpu()
function higher up in the file, so that __cpufreq_add_dev() can invoke
it).

Reported-and-tested-by: Stephen Warren 
Signed-off-by: Srivatsa S. Bhat 
Signed-off-by: Rafael J. Wysocki