[v2] cpufreq: powernv: fix stack bloat and NR_CPUS limitation
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Message ID 20191018045539.3765565-1-jhubbard@nvidia.com
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  • [v2] cpufreq: powernv: fix stack bloat and NR_CPUS limitation
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Commit Message

John Hubbard Oct. 18, 2019, 4:55 a.m. UTC
The following build warning occurred on powerpc 64-bit builds:

drivers/cpufreq/powernv-cpufreq.c: In function 'init_chip_info':
drivers/cpufreq/powernv-cpufreq.c:1070:1: warning: the frame size of 1040 bytes is larger than 1024 bytes [-Wframe-larger-than=]

This is due to putting 1024 bytes on the stack:

    unsigned int chip[256];

...and while looking at this, it also has a bug: it fails with a stack
overrun, if CONFIG_NR_CPUS > 256.

Fix both problems by dynamically allocating based on CONFIG_NR_CPUS.

Fixes: 053819e0bf840 ("cpufreq: powernv: Handle throttling due to Pmax capping at chip level")
Cc: Shilpasri G Bhat <shilpa.bhat@linux.vnet.ibm.com>
Cc: Preeti U Murthy <preeti@linux.vnet.ibm.com>
Cc: Viresh Kumar <viresh.kumar@linaro.org>
Cc: Rafael J. Wysocki <rjw@rjwysocki.net>
Cc: linux-pm@vger.kernel.org
Cc: linuxppc-dev@lists.ozlabs.org
Signed-off-by: John Hubbard <jhubbard@nvidia.com>
---

Changes since v1: includes Viresh's review commit fixes.

 drivers/cpufreq/powernv-cpufreq.c | 17 +++++++++++++----
 1 file changed, 13 insertions(+), 4 deletions(-)

Comments

Viresh Kumar Oct. 18, 2019, 5:07 a.m. UTC | #1
On 17-10-19, 21:55, John Hubbard wrote:
> The following build warning occurred on powerpc 64-bit builds:
> 
> drivers/cpufreq/powernv-cpufreq.c: In function 'init_chip_info':
> drivers/cpufreq/powernv-cpufreq.c:1070:1: warning: the frame size of 1040 bytes is larger than 1024 bytes [-Wframe-larger-than=]
> 
> This is due to putting 1024 bytes on the stack:
> 
>     unsigned int chip[256];
> 
> ...and while looking at this, it also has a bug: it fails with a stack
> overrun, if CONFIG_NR_CPUS > 256.
> 
> Fix both problems by dynamically allocating based on CONFIG_NR_CPUS.
> 
> Fixes: 053819e0bf840 ("cpufreq: powernv: Handle throttling due to Pmax capping at chip level")
> Cc: Shilpasri G Bhat <shilpa.bhat@linux.vnet.ibm.com>
> Cc: Preeti U Murthy <preeti@linux.vnet.ibm.com>
> Cc: Viresh Kumar <viresh.kumar@linaro.org>
> Cc: Rafael J. Wysocki <rjw@rjwysocki.net>
> Cc: linux-pm@vger.kernel.org
> Cc: linuxppc-dev@lists.ozlabs.org
> Signed-off-by: John Hubbard <jhubbard@nvidia.com>
> ---
> 
> Changes since v1: includes Viresh's review commit fixes.
> 
>  drivers/cpufreq/powernv-cpufreq.c | 17 +++++++++++++----
>  1 file changed, 13 insertions(+), 4 deletions(-)

Acked-by: Viresh Kumar <viresh.kumar@linaro.org>
Rafael J. Wysocki Oct. 28, 2019, 3:26 p.m. UTC | #2
On Friday, October 18, 2019 7:07:12 AM CET Viresh Kumar wrote:
> On 17-10-19, 21:55, John Hubbard wrote:
> > The following build warning occurred on powerpc 64-bit builds:
> > 
> > drivers/cpufreq/powernv-cpufreq.c: In function 'init_chip_info':
> > drivers/cpufreq/powernv-cpufreq.c:1070:1: warning: the frame size of 1040 bytes is larger than 1024 bytes [-Wframe-larger-than=]
> > 
> > This is due to putting 1024 bytes on the stack:
> > 
> >     unsigned int chip[256];
> > 
> > ...and while looking at this, it also has a bug: it fails with a stack
> > overrun, if CONFIG_NR_CPUS > 256.
> > 
> > Fix both problems by dynamically allocating based on CONFIG_NR_CPUS.
> > 
> > Fixes: 053819e0bf840 ("cpufreq: powernv: Handle throttling due to Pmax capping at chip level")
> > Cc: Shilpasri G Bhat <shilpa.bhat@linux.vnet.ibm.com>
> > Cc: Preeti U Murthy <preeti@linux.vnet.ibm.com>
> > Cc: Viresh Kumar <viresh.kumar@linaro.org>
> > Cc: Rafael J. Wysocki <rjw@rjwysocki.net>
> > Cc: linux-pm@vger.kernel.org
> > Cc: linuxppc-dev@lists.ozlabs.org
> > Signed-off-by: John Hubbard <jhubbard@nvidia.com>
> > ---
> > 
> > Changes since v1: includes Viresh's review commit fixes.
> > 
> >  drivers/cpufreq/powernv-cpufreq.c | 17 +++++++++++++----
> >  1 file changed, 13 insertions(+), 4 deletions(-)
> 
> Acked-by: Viresh Kumar <viresh.kumar@linaro.org>
> 
> 

Applying as 5.5 material, thanks!
Michael Ellerman Oct. 31, 2019, 2:39 a.m. UTC | #3
Hi John,

Sorry I didn't reply to this sooner, too many patches :/

John Hubbard <jhubbard@nvidia.com> writes:
> The following build warning occurred on powerpc 64-bit builds:
>
> drivers/cpufreq/powernv-cpufreq.c: In function 'init_chip_info':
> drivers/cpufreq/powernv-cpufreq.c:1070:1: warning: the frame size of 1040 bytes is larger than 1024 bytes [-Wframe-larger-than=]

Oddly I don't see that warning in my builds, eg with GCC9:

  https://travis-ci.org/linuxppc/linux/jobs/604870722

> This is due to putting 1024 bytes on the stack:
>
>     unsigned int chip[256];
>
> ...and while looking at this, it also has a bug: it fails with a stack
> overrun, if CONFIG_NR_CPUS > 256.

It _probably_ doesn't, because it only increments the index when the
chip_id of the CPU changes, ie. it doesn't create a chip for every CPU.
But I agree it's flaky the way it's written.

> Fix both problems by dynamically allocating based on CONFIG_NR_CPUS.

Shouldn't it use num_possible_cpus() ?

Given the for loop is over possible CPUs that seems like the upper
bound. In practice it should be lower because some CPUs will share a
chip.

cheers


> Fixes: 053819e0bf840 ("cpufreq: powernv: Handle throttling due to Pmax capping at chip level")
> Cc: Shilpasri G Bhat <shilpa.bhat@linux.vnet.ibm.com>
> Cc: Preeti U Murthy <preeti@linux.vnet.ibm.com>
> Cc: Viresh Kumar <viresh.kumar@linaro.org>
> Cc: Rafael J. Wysocki <rjw@rjwysocki.net>
> Cc: linux-pm@vger.kernel.org
> Cc: linuxppc-dev@lists.ozlabs.org
> Signed-off-by: John Hubbard <jhubbard@nvidia.com>
> ---
>
> Changes since v1: includes Viresh's review commit fixes.
>
>  drivers/cpufreq/powernv-cpufreq.c | 17 +++++++++++++----
>  1 file changed, 13 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/cpufreq/powernv-cpufreq.c b/drivers/cpufreq/powernv-cpufreq.c
> index 6061850e59c9..5b2e968cb5ea 100644
> --- a/drivers/cpufreq/powernv-cpufreq.c
> +++ b/drivers/cpufreq/powernv-cpufreq.c
> @@ -1041,9 +1041,14 @@ static struct cpufreq_driver powernv_cpufreq_driver = {
>  
>  static int init_chip_info(void)
>  {
> -	unsigned int chip[256];
> +	unsigned int *chip;
>  	unsigned int cpu, i;
>  	unsigned int prev_chip_id = UINT_MAX;
> +	int ret = 0;
> +
> +	chip = kcalloc(CONFIG_NR_CPUS, sizeof(*chip), GFP_KERNEL);
> +	if (!chip)
> +		return -ENOMEM;
>  
>  	for_each_possible_cpu(cpu) {
>  		unsigned int id = cpu_to_chip_id(cpu);
> @@ -1055,8 +1060,10 @@ static int init_chip_info(void)
>  	}
>  
>  	chips = kcalloc(nr_chips, sizeof(struct chip), GFP_KERNEL);
> -	if (!chips)
> -		return -ENOMEM;
> +	if (!chips) {
> +		ret = -ENOMEM;
> +		goto free_and_return;
> +	}
>  
>  	for (i = 0; i < nr_chips; i++) {
>  		chips[i].id = chip[i];
> @@ -1066,7 +1073,9 @@ static int init_chip_info(void)
>  			per_cpu(chip_info, cpu) =  &chips[i];
>  	}
>  
> -	return 0;
> +free_and_return:
> +	kfree(chip);
> +	return ret;
>  }
>  
>  static inline void clean_chip_info(void)
> -- 
> 2.23.0
John Hubbard Oct. 31, 2019, 5:17 a.m. UTC | #4
On 10/30/19 7:39 PM, Michael Ellerman wrote:
> Hi John,
> 
> Sorry I didn't reply to this sooner, too many patches :/
> 
> John Hubbard <jhubbard@nvidia.com> writes:
>> The following build warning occurred on powerpc 64-bit builds:
>>
>> drivers/cpufreq/powernv-cpufreq.c: In function 'init_chip_info':
>> drivers/cpufreq/powernv-cpufreq.c:1070:1: warning: the frame size of 1040 bytes is larger than 1024 bytes [-Wframe-larger-than=]
> 
> Oddly I don't see that warning in my builds, eg with GCC9:
> 
>    https://travis-ci.org/linuxppc/linux/jobs/604870722

This is with a cross-compiler based on gcc 8.1.0, which I got from:
   https://mirrors.edge.kernel.org/pub/tools/crosstool/files/bin/x86_64/8.1.0/

I'll put that in the v3 commit description.

> 
>> This is due to putting 1024 bytes on the stack:
>>
>>      unsigned int chip[256];
>>
>> ...and while looking at this, it also has a bug: it fails with a stack
>> overrun, if CONFIG_NR_CPUS > 256.
> 
> It _probably_ doesn't, because it only increments the index when the
> chip_id of the CPU changes, ie. it doesn't create a chip for every CPU.
> But I agree it's flaky the way it's written.

I'll soften up the wording accordingly.

> 
>> Fix both problems by dynamically allocating based on CONFIG_NR_CPUS.
> 
> Shouldn't it use num_possible_cpus() ?
> 
> Given the for loop is over possible CPUs that seems like the upper
> bound. In practice it should be lower because some CPUs will share a
> chip.
> 

OK, I see, that's more consistent with the code, I'll change to that.


thanks,
Michael Ellerman Nov. 6, 2019, 3:35 a.m. UTC | #5
John Hubbard <jhubbard@nvidia.com> writes:
> On 10/30/19 7:39 PM, Michael Ellerman wrote:
>> Hi John,
>> 
>> Sorry I didn't reply to this sooner, too many patches :/
>> 
>> John Hubbard <jhubbard@nvidia.com> writes:
>>> The following build warning occurred on powerpc 64-bit builds:
>>>
>>> drivers/cpufreq/powernv-cpufreq.c: In function 'init_chip_info':
>>> drivers/cpufreq/powernv-cpufreq.c:1070:1: warning: the frame size of 1040 bytes is larger than 1024 bytes [-Wframe-larger-than=]
>> 
>> Oddly I don't see that warning in my builds, eg with GCC9:
>> 
>>    https://travis-ci.org/linuxppc/linux/jobs/604870722
>
> This is with a cross-compiler based on gcc 8.1.0, which I got from:
>    https://mirrors.edge.kernel.org/pub/tools/crosstool/files/bin/x86_64/8.1.0/
>
> I'll put that in the v3 commit description.
>
>> 
>>> This is due to putting 1024 bytes on the stack:
>>>
>>>      unsigned int chip[256];
>>>
>>> ...and while looking at this, it also has a bug: it fails with a stack
>>> overrun, if CONFIG_NR_CPUS > 256.
>> 
>> It _probably_ doesn't, because it only increments the index when the
>> chip_id of the CPU changes, ie. it doesn't create a chip for every CPU.
>> But I agree it's flaky the way it's written.
>
> I'll soften up the wording accordingly.
>
>> 
>>> Fix both problems by dynamically allocating based on CONFIG_NR_CPUS.
>> 
>> Shouldn't it use num_possible_cpus() ?
>> 
>> Given the for loop is over possible CPUs that seems like the upper
>> bound. In practice it should be lower because some CPUs will share a
>> chip.
>> 
>
> OK, I see, that's more consistent with the code, I'll change to that.

Thanks.

cheers

Patch
diff mbox series

diff --git a/drivers/cpufreq/powernv-cpufreq.c b/drivers/cpufreq/powernv-cpufreq.c
index 6061850e59c9..5b2e968cb5ea 100644
--- a/drivers/cpufreq/powernv-cpufreq.c
+++ b/drivers/cpufreq/powernv-cpufreq.c
@@ -1041,9 +1041,14 @@  static struct cpufreq_driver powernv_cpufreq_driver = {
 
 static int init_chip_info(void)
 {
-	unsigned int chip[256];
+	unsigned int *chip;
 	unsigned int cpu, i;
 	unsigned int prev_chip_id = UINT_MAX;
+	int ret = 0;
+
+	chip = kcalloc(CONFIG_NR_CPUS, sizeof(*chip), GFP_KERNEL);
+	if (!chip)
+		return -ENOMEM;
 
 	for_each_possible_cpu(cpu) {
 		unsigned int id = cpu_to_chip_id(cpu);
@@ -1055,8 +1060,10 @@  static int init_chip_info(void)
 	}
 
 	chips = kcalloc(nr_chips, sizeof(struct chip), GFP_KERNEL);
-	if (!chips)
-		return -ENOMEM;
+	if (!chips) {
+		ret = -ENOMEM;
+		goto free_and_return;
+	}
 
 	for (i = 0; i < nr_chips; i++) {
 		chips[i].id = chip[i];
@@ -1066,7 +1073,9 @@  static int init_chip_info(void)
 			per_cpu(chip_info, cpu) =  &chips[i];
 	}
 
-	return 0;
+free_and_return:
+	kfree(chip);
+	return ret;
 }
 
 static inline void clean_chip_info(void)