padata: Honor the caller's alignment in case of chunk_size 0

In the case where we are forcing the ps.chunk_size to be at least 1,
we are ignoring the caller's alignment.

Move the forcing of ps.chunk_size to be at least 1 before rounding it
up to caller's alignment, so that caller's alignment is honored.

While at it, use max() to force the ps.chunk_size to be at least 1 to
improve readability.

Fixes: 6d45e1c948a8 ("padata: Fix possible divide-by-0 panic in padata_mt_helper()")
Signed-off-by: Kamlesh Gurudasani <kamlesh@ti.com>
---
 kernel/padata.c | 12 ++++--------
 1 file changed, 4 insertions(+), 8 deletions(-)


---
base-commit: b311c1b497e51a628aa89e7cb954481e5f9dced2
change-id: 20240822-max-93c17adc6457

Best regards,

On Thu, Aug 22, 2024 at 02:32:52AM GMT, Kamlesh Gurudasani wrote:
> In the case where we are forcing the ps.chunk_size to be at least 1,
> we are ignoring the caller's alignment.
> 
> Move the forcing of ps.chunk_size to be at least 1 before rounding it
> up to caller's alignment, so that caller's alignment is honored.
> 
> While at it, use max() to force the ps.chunk_size to be at least 1 to
> improve readability.
> 
> Fixes: 6d45e1c948a8 ("padata: Fix possible divide-by-0 panic in padata_mt_helper()")

Looks fine.

Acked-by: Daniel Jordan <daniel.m.jordan@oracle.com>

> Signed-off-by: Kamlesh Gurudasani <kamlesh@ti.com>
> ---
>  kernel/padata.c | 12 ++++--------
>  1 file changed, 4 insertions(+), 8 deletions(-)
> 
> diff --git a/kernel/padata.c b/kernel/padata.c
> index 0fa6c2895460..d8a51eff1581 100644
> --- a/kernel/padata.c
> +++ b/kernel/padata.c
> @@ -509,21 +509,17 @@ void __init padata_do_multithreaded(struct padata_mt_job *job)
>  
>  	/*
>  	 * Chunk size is the amount of work a helper does per call to the
> -	 * thread function.  Load balance large jobs between threads by
> +	 * thread function. Load balance large jobs between threads by

Though whitespace changes like these just add noise...

Andrew Morton <akpm@linux-foundation.org> writes:

> This message was sent from outside of Texas Instruments. 
> Do not click links or open attachments unless you recognize the source of this email and know the content is safe. 
> Report Suspicious 
>  
> On Thu, 22 Aug 2024 02:32:52 +0530 Kamlesh Gurudasani <kamlesh@ti.com> wrote:
>
>> In the case where we are forcing the ps.chunk_size to be at least 1,
>> we are ignoring the caller's alignment.
>> 
>> Move the forcing of ps.chunk_size to be at least 1 before rounding it
>> up to caller's alignment, so that caller's alignment is honored.
>> 
>> While at it, use max() to force the ps.chunk_size to be at least 1 to
>> improve readability.
>
> Please (as always) describe the userspace-visible runtime effects of
> this change.  This helps others to determine which kernel(s) should be
> patched.  And it helps others decide whether this fix might address an
> issue which they are encountering.

Thanks for the review, Andrew.
Honestly, I'm not sure the effects would be visble to userspace or not.
or even how to reproduce it.

I have fixed according to discussion here,
https://patchwork.kernel.org/project/linux-crypto/patch/20240806174647.1050398-1-longman@redhat.com/#25984314

Kamlesh

Daniel Jordan <daniel.m.jordan@oracle.com> writes:

> On Thu, Aug 22, 2024 at 02:32:52AM GMT, Kamlesh Gurudasani wrote:
>> In the case where we are forcing the ps.chunk_size to be at least 1,
>> we are ignoring the caller's alignment.
>> 
>> Move the forcing of ps.chunk_size to be at least 1 before rounding it
>> up to caller's alignment, so that caller's alignment is honored.
>> 
>> While at it, use max() to force the ps.chunk_size to be at least 1 to
>> improve readability.
>> 
>> Fixes: 6d45e1c948a8 ("padata: Fix possible divide-by-0 panic in padata_mt_helper()")
>
> Looks fine.
>
> Acked-by: Daniel Jordan <daniel.m.jordan@oracle.com>
>
>> Signed-off-by: Kamlesh Gurudasani <kamlesh@ti.com>
>> ---
>>  kernel/padata.c | 12 ++++--------
>>  1 file changed, 4 insertions(+), 8 deletions(-)
>> 
>> diff --git a/kernel/padata.c b/kernel/padata.c
>> index 0fa6c2895460..d8a51eff1581 100644
>> --- a/kernel/padata.c
>> +++ b/kernel/padata.c
>> @@ -509,21 +509,17 @@ void __init padata_do_multithreaded(struct padata_mt_job *job)
>>  
>>  	/*
>>  	 * Chunk size is the amount of work a helper does per call to the
>> -	 * thread function.  Load balance large jobs between threads by
>> +	 * thread function. Load balance large jobs between threads by
>
> Though whitespace changes like these just add noise...
Thanks for the Ack, would keep these in mind from next time onwards.

Kamlesh

Waiman Long <longman@redhat.com> writes:

> This message was sent from outside of Texas Instruments. 
> Do not click links or open attachments unless you recognize the source of this email and know the content is safe. 
> Report Suspicious 
>  
> On 8/21/24 17:02, Kamlesh Gurudasani wrote:
>> In the case where we are forcing the ps.chunk_size to be at least 1,
>> we are ignoring the caller's alignment.
>>
>> Move the forcing of ps.chunk_size to be at least 1 before rounding it
>> up to caller's alignment, so that caller's alignment is honored.
>>
>> While at it, use max() to force the ps.chunk_size to be at least 1 to
>> improve readability.
>>
>> Fixes: 6d45e1c948a8 ("padata: Fix possible divide-by-0 panic in padata_mt_helper()")
>> Signed-off-by: Kamlesh Gurudasani <kamlesh@ti.com>
>> ---
>>   kernel/padata.c | 12 ++++--------
>>   1 file changed, 4 insertions(+), 8 deletions(-)
>>
>> diff --git a/kernel/padata.c b/kernel/padata.c
>> index 0fa6c2895460..d8a51eff1581 100644
>> --- a/kernel/padata.c
>> +++ b/kernel/padata.c
>> @@ -509,21 +509,17 @@ void __init padata_do_multithreaded(struct padata_mt_job *job)
>>   
>>   	/*
>>   	 * Chunk size is the amount of work a helper does per call to the
>> -	 * thread function.  Load balance large jobs between threads by
>> +	 * thread function. Load balance large jobs between threads by
>>   	 * increasing the number of chunks, guarantee at least the minimum
>>   	 * chunk size from the caller, and honor the caller's alignment.
>> +	 * Ensure chunk_size is at least 1 to prevent divide-by-0
>> +	 * panic in padata_mt_helper().
>>   	 */
>>   	ps.chunk_size = job->size / (ps.nworks * load_balance_factor);
>>   	ps.chunk_size = max(ps.chunk_size, job->min_chunk);
>> +	ps.chunk_size = max(ps.chunk_size, 1ul);
>>   	ps.chunk_size = roundup(ps.chunk_size, job->align);
>>   
>> -	/*
>> -	 * chunk_size can be 0 if the caller sets min_chunk to 0. So force it
>> -	 * to at least 1 to prevent divide-by-0 panic in padata_mt_helper().`
>> -	 */
>> -	if (!ps.chunk_size)
>> -		ps.chunk_size = 1U;
>> -
>>   	list_for_each_entry(pw, &works, pw_list)
>>   		if (job->numa_aware) {
>>   			int old_node = atomic_read(&last_used_nid);
>>
>> ---
>> base-commit: b311c1b497e51a628aa89e7cb954481e5f9dced2
>> change-id: 20240822-max-93c17adc6457
>
> LGTM, my only nit is the use of "1ul" which is less common and harder to 
> read than "1UL" as the former one may be misread as a "lul" variable.
>
> Acked-by:  Waiman Long <longman@redhat.com>
Thanks for the Acked-by, Waiman. I understand your point, though Daniel seems
to be okay with this, so will keep it as is this time.

Cheers,
Kamlesh

On 8/25/24 07:34, Kamlesh Gurudasani wrote:
> Waiman Long <longman@redhat.com> writes:
>
>> This message was sent from outside of Texas Instruments.
>> Do not click links or open attachments unless you recognize the source of this email and know the content is safe.
>> Report Suspicious
>>   
>> On 8/21/24 17:02, Kamlesh Gurudasani wrote:
>>> In the case where we are forcing the ps.chunk_size to be at least 1,
>>> we are ignoring the caller's alignment.
>>>
>>> Move the forcing of ps.chunk_size to be at least 1 before rounding it
>>> up to caller's alignment, so that caller's alignment is honored.
>>>
>>> While at it, use max() to force the ps.chunk_size to be at least 1 to
>>> improve readability.
>>>
>>> Fixes: 6d45e1c948a8 ("padata: Fix possible divide-by-0 panic in padata_mt_helper()")
>>> Signed-off-by: Kamlesh Gurudasani <kamlesh@ti.com>
>>> ---
>>>    kernel/padata.c | 12 ++++--------
>>>    1 file changed, 4 insertions(+), 8 deletions(-)
>>>
>>> diff --git a/kernel/padata.c b/kernel/padata.c
>>> index 0fa6c2895460..d8a51eff1581 100644
>>> --- a/kernel/padata.c
>>> +++ b/kernel/padata.c
>>> @@ -509,21 +509,17 @@ void __init padata_do_multithreaded(struct padata_mt_job *job)
>>>    
>>>    	/*
>>>    	 * Chunk size is the amount of work a helper does per call to the
>>> -	 * thread function.  Load balance large jobs between threads by
>>> +	 * thread function. Load balance large jobs between threads by
>>>    	 * increasing the number of chunks, guarantee at least the minimum
>>>    	 * chunk size from the caller, and honor the caller's alignment.
>>> +	 * Ensure chunk_size is at least 1 to prevent divide-by-0
>>> +	 * panic in padata_mt_helper().
>>>    	 */
>>>    	ps.chunk_size = job->size / (ps.nworks * load_balance_factor);
>>>    	ps.chunk_size = max(ps.chunk_size, job->min_chunk);
>>> +	ps.chunk_size = max(ps.chunk_size, 1ul);
>>>    	ps.chunk_size = roundup(ps.chunk_size, job->align);
>>>    
>>> -	/*
>>> -	 * chunk_size can be 0 if the caller sets min_chunk to 0. So force it
>>> -	 * to at least 1 to prevent divide-by-0 panic in padata_mt_helper().`
>>> -	 */
>>> -	if (!ps.chunk_size)
>>> -		ps.chunk_size = 1U;
>>> -
>>>    	list_for_each_entry(pw, &works, pw_list)
>>>    		if (job->numa_aware) {
>>>    			int old_node = atomic_read(&last_used_nid);
>>>
>>> ---
>>> base-commit: b311c1b497e51a628aa89e7cb954481e5f9dced2
>>> change-id: 20240822-max-93c17adc6457
>> LGTM, my only nit is the use of "1ul" which is less common and harder to
>> read than "1UL" as the former one may be misread as a "lul" variable.
>>
>> Acked-by:  Waiman Long <longman@redhat.com>
> Thanks for the Acked-by, Waiman. I understand your point, though Daniel seems
> to be okay with this, so will keep it as is this time.

This is just a suggestion in case you need to update your patch. I am 
fine with keeping it as is if no further update is needed.

Cheers,
Longman

On Thu, Aug 22, 2024 at 02:32:52AM +0530, Kamlesh Gurudasani wrote:
> In the case where we are forcing the ps.chunk_size to be at least 1,
> we are ignoring the caller's alignment.
> 
> Move the forcing of ps.chunk_size to be at least 1 before rounding it
> up to caller's alignment, so that caller's alignment is honored.
> 
> While at it, use max() to force the ps.chunk_size to be at least 1 to
> improve readability.
> 
> Fixes: 6d45e1c948a8 ("padata: Fix possible divide-by-0 panic in padata_mt_helper()")
> Signed-off-by: Kamlesh Gurudasani <kamlesh@ti.com>
> ---
>  kernel/padata.c | 12 ++++--------
>  1 file changed, 4 insertions(+), 8 deletions(-)

Patch applied.  Thanks.