cpufreq:powernv: Fix init_chip_info initialization in numa=off

Message ID 20210615050949.10071-1-psampat@linux.ibm.com
State New
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Series
  • cpufreq:powernv: Fix init_chip_info initialization in numa=off
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Commit Message

Pratik R. Sampat June 15, 2021, 5:09 a.m.
In the numa=off kernel command-line configuration init_chip_info() loops
around the number of chips and attempts to copy the cpumask of that node
which is NULL for all iterations after the first chip.

Hence adding a check to bail out after the first initialization if there
is only one node.

Fixes: 053819e0bf84 ("cpufreq: powernv: Handle throttling due to Pmax capping at chip level")
Signed-off-by: Pratik R. Sampat <psampat@linux.ibm.com>
Reported-by: Shirisha Ganta <shirishaganta1@ibm.com>
---
 drivers/cpufreq/powernv-cpufreq.c | 2 ++
 1 file changed, 2 insertions(+)

Comments

Gautham R. Shenoy July 8, 2021, 9:08 a.m. | #1
Hello Pratik,

On Tue, Jun 15, 2021 at 10:39:49AM +0530, Pratik R. Sampat wrote:
> In the numa=off kernel command-line configuration init_chip_info() loops

> around the number of chips and attempts to copy the cpumask of that node

> which is NULL for all iterations after the first chip.


Thanks for taking a look into this. Indeed there is an issue here
because the code here assumes that node_mask as a proxy for the
chip_mask. This assumption breaks when run with numa=off, since there will only be a
single node, but multiple chips.


> 

> Hence adding a check to bail out after the first initialization if there

> is only one node.

> 

> Fixes: 053819e0bf84 ("cpufreq: powernv: Handle throttling due to Pmax capping at chip level")

> Signed-off-by: Pratik R. Sampat <psampat@linux.ibm.com>

> Reported-by: Shirisha Ganta <shirishaganta1@ibm.com>

> ---

>  drivers/cpufreq/powernv-cpufreq.c | 2 ++

>  1 file changed, 2 insertions(+)

> 

> diff --git a/drivers/cpufreq/powernv-cpufreq.c b/drivers/cpufreq/powernv-cpufreq.c

> index e439b43c19eb..663f9c4b5e3a 100644

> --- a/drivers/cpufreq/powernv-cpufreq.c

> +++ b/drivers/cpufreq/powernv-cpufreq.c

> @@ -1078,6 +1078,8 @@ static int init_chip_info(void)

>  		INIT_WORK(&chips[i].throttle, powernv_cpufreq_work_fn);

>  		for_each_cpu(cpu, &chips[i].mask)

>  			per_cpu(chip_info, cpu) =  &chips[i];

> +		if (num_possible_nodes() == 1)

> +			break;


With this we will only initialize the chip[0].throttle work function,
while for the rest of the chips chip[i].throttle will be
uninitialized. While we may be running in the numa=off mode, the fact
remains that those other chips do exist and they may experiencing
throttling, during which they will try to schedule work for chip[i] in
order to take corrective action, which will fail.

Hence a more correct approach may be to maintain a chip[i] mask
independent of the node mask.





>  	}

>  

>  free_and_return:

> -- 

> 2.30.2

>

Patch

diff --git a/drivers/cpufreq/powernv-cpufreq.c b/drivers/cpufreq/powernv-cpufreq.c
index e439b43c19eb..663f9c4b5e3a 100644
--- a/drivers/cpufreq/powernv-cpufreq.c
+++ b/drivers/cpufreq/powernv-cpufreq.c
@@ -1078,6 +1078,8 @@  static int init_chip_info(void)
 		INIT_WORK(&chips[i].throttle, powernv_cpufreq_work_fn);
 		for_each_cpu(cpu, &chips[i].mask)
 			per_cpu(chip_info, cpu) =  &chips[i];
+		if (num_possible_nodes() == 1)
+			break;
 	}
 
 free_and_return: