* [PATCH] percpu: initialize best_upa variable
@ 2021-05-15 18:08 trix
2021-05-16 23:45 ` Wonhyuk Yang
2021-05-17 2:05 ` Dennis Zhou
0 siblings, 2 replies; 8+ messages in thread
From: trix @ 2021-05-15 18:08 UTC (permalink / raw)
To: dennis, tj, cl, akpm; +Cc: linux-mm, linux-kernel, Tom Rix
From: Tom Rix <trix@redhat.com>
Static analysis reports this problem
percpu.c:2945:6: warning: Assigned value is garbage or undefined
upa = best_upa;
^ ~~~~~~~~
best_upa may not be set, so initialize it.
Signed-off-by: Tom Rix <trix@redhat.com>
---
mm/percpu.c | 1 +
1 file changed, 1 insertion(+)
diff --git a/mm/percpu.c b/mm/percpu.c
index a257c3efdf18b..6578b706fae81 100644
--- a/mm/percpu.c
+++ b/mm/percpu.c
@@ -2916,6 +2916,7 @@ static struct pcpu_alloc_info * __init __flatten pcpu_build_alloc_info(
* Related to atom_size, which could be much larger than the unit_size.
*/
last_allocs = INT_MAX;
+ best_upa = max_upa;
for (upa = max_upa; upa; upa--) {
int allocs = 0, wasted = 0;
--
2.26.3
^ permalink raw reply related [flat|nested] 8+ messages in thread
* Re: [PATCH] percpu: initialize best_upa variable
2021-05-15 18:08 [PATCH] percpu: initialize best_upa variable trix
@ 2021-05-16 23:45 ` Wonhyuk Yang
2021-05-17 2:05 ` Dennis Zhou
1 sibling, 0 replies; 8+ messages in thread
From: Wonhyuk Yang @ 2021-05-16 23:45 UTC (permalink / raw)
To: trix
Cc: Dennis Zhou, Tejun Heo, Christoph Lameter, Andrew Morton,
linux-mm, linux-kernel
On Sun, May 16, 2021 at 3:08 AM <trix@redhat.com> wrote:
> Static analysis reports this problem
> percpu.c:2945:6: warning: Assigned value is garbage or undefined
> upa = best_upa;
> ^ ~~~~~~~~
> best_upa may not be set, so initialize it.
Hi,
Actually, best_upa is always set in the for loop below. when upa is 1,
It will always satisfy all conditions.
> diff --git a/mm/percpu.c b/mm/percpu.c
> index a257c3efdf18b..6578b706fae81 100644
> --- a/mm/percpu.c
> +++ b/mm/percpu.c
> @@ -2916,6 +2916,7 @@ static struct pcpu_alloc_info * __init __flatten pcpu_build_alloc_info(
> * Related to atom_size, which could be much larger than the unit_size.
> */
> last_allocs = INT_MAX;
> + best_upa = max_upa;
> for (upa = max_upa; upa; upa--) {
> int allocs = 0, wasted = 0;
It doesn't seem to be a problem. But, how about this?
best_upa = 1;
for (upa = max_upa; upa>1; upa--)
^ permalink raw reply [flat|nested] 8+ messages in thread
* Re: [PATCH] percpu: initialize best_upa variable
2021-05-15 18:08 [PATCH] percpu: initialize best_upa variable trix
2021-05-16 23:45 ` Wonhyuk Yang
@ 2021-05-17 2:05 ` Dennis Zhou
2021-05-17 11:06 ` Wonhyuk Yang
2021-05-17 13:17 ` Tom Rix
1 sibling, 2 replies; 8+ messages in thread
From: Dennis Zhou @ 2021-05-17 2:05 UTC (permalink / raw)
To: trix; +Cc: tj, cl, akpm, linux-mm, linux-kernel
Hello,
On Sat, May 15, 2021 at 11:08:17AM -0700, trix@redhat.com wrote:
> From: Tom Rix <trix@redhat.com>
>
> Static analysis reports this problem
> percpu.c:2945:6: warning: Assigned value is garbage or undefined
> upa = best_upa;
> ^ ~~~~~~~~
> best_upa may not be set, so initialize it.
>
> Signed-off-by: Tom Rix <trix@redhat.com>
> ---
> mm/percpu.c | 1 +
> 1 file changed, 1 insertion(+)
>
> diff --git a/mm/percpu.c b/mm/percpu.c
> index a257c3efdf18b..6578b706fae81 100644
> --- a/mm/percpu.c
> +++ b/mm/percpu.c
> @@ -2916,6 +2916,7 @@ static struct pcpu_alloc_info * __init __flatten pcpu_build_alloc_info(
> * Related to atom_size, which could be much larger than the unit_size.
> */
> last_allocs = INT_MAX;
> + best_upa = max_upa;
> for (upa = max_upa; upa; upa--) {
> int allocs = 0, wasted = 0;
>
> --
> 2.26.3
>
I think the proper fix would be:
best_upa = 0;
for (...) { }
BUG_ON(!best_upa);
upa = best_upa;
If you're fine with this I'll make the changes and apply it to
for-5.13-fixes.
Can you also tell me what static analysis tool produced this? I'm just a
little curious because this code hasn't changed in several years so I'd
have expected some static analyzer to have caught this by now.
Thanks,
Dennis
^ permalink raw reply [flat|nested] 8+ messages in thread
* Re: [PATCH] percpu: initialize best_upa variable
2021-05-17 2:05 ` Dennis Zhou
@ 2021-05-17 11:06 ` Wonhyuk Yang
2021-05-17 13:17 ` Tom Rix
1 sibling, 0 replies; 8+ messages in thread
From: Wonhyuk Yang @ 2021-05-17 11:06 UTC (permalink / raw)
To: Dennis Zhou
Cc: trix, Tejun Heo, Christoph Lameter, Andrew Morton, linux-mm,
linux-kernel
On Mon, May 17, 2021 at 11:05 AM Dennis Zhou <dennis@kernel.org> wrote:
>
> Can you also tell me what static analysis tool produced this? I'm just a
> little curious because this code hasn't changed in several years so I'd
> have expected some static analyzer to have caught this by now.
>
It's because uninitialize_var() was gone. It was introduced commit :
3f649ab728cda8("treewide: Remove uninitialized_var() usage")
^ permalink raw reply [flat|nested] 8+ messages in thread
* Re: [PATCH] percpu: initialize best_upa variable
2021-05-17 2:05 ` Dennis Zhou
2021-05-17 11:06 ` Wonhyuk Yang
@ 2021-05-17 13:17 ` Tom Rix
2021-05-17 14:39 ` Dennis Zhou
1 sibling, 1 reply; 8+ messages in thread
From: Tom Rix @ 2021-05-17 13:17 UTC (permalink / raw)
To: Dennis Zhou; +Cc: tj, cl, akpm, linux-mm, linux-kernel
On 5/16/21 7:05 PM, Dennis Zhou wrote:
> Hello,
>
> On Sat, May 15, 2021 at 11:08:17AM -0700, trix@redhat.com wrote:
>> From: Tom Rix <trix@redhat.com>
>>
>> Static analysis reports this problem
>> percpu.c:2945:6: warning: Assigned value is garbage or undefined
>> upa = best_upa;
>> ^ ~~~~~~~~
>> best_upa may not be set, so initialize it.
>>
>> Signed-off-by: Tom Rix <trix@redhat.com>
>> ---
>> mm/percpu.c | 1 +
>> 1 file changed, 1 insertion(+)
>>
>> diff --git a/mm/percpu.c b/mm/percpu.c
>> index a257c3efdf18b..6578b706fae81 100644
>> --- a/mm/percpu.c
>> +++ b/mm/percpu.c
>> @@ -2916,6 +2916,7 @@ static struct pcpu_alloc_info * __init __flatten pcpu_build_alloc_info(
>> * Related to atom_size, which could be much larger than the unit_size.
>> */
>> last_allocs = INT_MAX;
>> + best_upa = max_upa;
>> for (upa = max_upa; upa; upa--) {
>> int allocs = 0, wasted = 0;
>>
>> --
>> 2.26.3
>>
> I think the proper fix would be:
>
> best_upa = 0;
I was looking for initializing with something that would work.
> for (...) { }
> BUG_ON(!best_upa);
WARN_ON instead?
> upa = best_upa;
>
> If you're fine with this I'll make the changes and apply it to
> for-5.13-fixes.
>
> Can you also tell me what static analysis tool produced this? I'm just a
> little curious because this code hasn't changed in several years so I'd
> have expected some static analyzer to have caught this by now.
Clang 10
Tom
>
> Thanks,
> Dennis
>
^ permalink raw reply [flat|nested] 8+ messages in thread
* Re: [PATCH] percpu: initialize best_upa variable
2021-05-17 13:17 ` Tom Rix
@ 2021-05-17 14:39 ` Dennis Zhou
2021-05-27 20:24 ` Dennis Zhou
0 siblings, 1 reply; 8+ messages in thread
From: Dennis Zhou @ 2021-05-17 14:39 UTC (permalink / raw)
To: Tom Rix; +Cc: tj, cl, akpm, linux-mm, linux-kernel
On Mon, May 17, 2021 at 06:17:47AM -0700, Tom Rix wrote:
>
> On 5/16/21 7:05 PM, Dennis Zhou wrote:
> > Hello,
> >
> > On Sat, May 15, 2021 at 11:08:17AM -0700, trix@redhat.com wrote:
> > > From: Tom Rix <trix@redhat.com>
> > >
> > > Static analysis reports this problem
> > > percpu.c:2945:6: warning: Assigned value is garbage or undefined
> > > upa = best_upa;
> > > ^ ~~~~~~~~
> > > best_upa may not be set, so initialize it.
> > >
> > > Signed-off-by: Tom Rix <trix@redhat.com>
> > > ---
> > > mm/percpu.c | 1 +
> > > 1 file changed, 1 insertion(+)
> > >
> > > diff --git a/mm/percpu.c b/mm/percpu.c
> > > index a257c3efdf18b..6578b706fae81 100644
> > > --- a/mm/percpu.c
> > > +++ b/mm/percpu.c
> > > @@ -2916,6 +2916,7 @@ static struct pcpu_alloc_info * __init __flatten pcpu_build_alloc_info(
> > > * Related to atom_size, which could be much larger than the unit_size.
> > > */
> > > last_allocs = INT_MAX;
> > > + best_upa = max_upa;
> > > for (upa = max_upa; upa; upa--) {
> > > int allocs = 0, wasted = 0;
> > > --
> > > 2.26.3
> > >
> > I think the proper fix would be:
> >
> > best_upa = 0;
>
> I was looking for initializing with something that would work.
>
I think I prefer setting it to 0 because it forces the loop to have
succeeded vs being able to bypass it if the for loop logic was changed.
> > for (...) { }
> > BUG_ON(!best_upa);
> WARN_ON instead?
This is initialization code. So if upa == 0, it really is a problem.
Having 0 units per allocation is bogus.
> > upa = best_upa;
> >
> > If you're fine with this I'll make the changes and apply it to
> > for-5.13-fixes.
> >
> > Can you also tell me what static analysis tool produced this? I'm just a
> > little curious because this code hasn't changed in several years so I'd
> > have expected some static analyzer to have caught this by now.
>
> Clang 10
>
> Tom
>
Thanks,
Dennis
^ permalink raw reply [flat|nested] 8+ messages in thread
* Re: [PATCH] percpu: initialize best_upa variable
2021-05-17 14:39 ` Dennis Zhou
@ 2021-05-27 20:24 ` Dennis Zhou
2021-05-27 21:09 ` Tom Rix
0 siblings, 1 reply; 8+ messages in thread
From: Dennis Zhou @ 2021-05-27 20:24 UTC (permalink / raw)
To: Tom Rix; +Cc: tj, cl, akpm, linux-mm, linux-kernel
Hello,
On Mon, May 17, 2021 at 02:39:21PM +0000, Dennis Zhou wrote:
> On Mon, May 17, 2021 at 06:17:47AM -0700, Tom Rix wrote:
> >
> > On 5/16/21 7:05 PM, Dennis Zhou wrote:
> > > Hello,
> > >
> > > On Sat, May 15, 2021 at 11:08:17AM -0700, trix@redhat.com wrote:
> > > > From: Tom Rix <trix@redhat.com>
> > > >
> > > > Static analysis reports this problem
> > > > percpu.c:2945:6: warning: Assigned value is garbage or undefined
> > > > upa = best_upa;
> > > > ^ ~~~~~~~~
> > > > best_upa may not be set, so initialize it.
> > > >
> > > > Signed-off-by: Tom Rix <trix@redhat.com>
> > > > ---
> > > > mm/percpu.c | 1 +
> > > > 1 file changed, 1 insertion(+)
> > > >
> > > > diff --git a/mm/percpu.c b/mm/percpu.c
> > > > index a257c3efdf18b..6578b706fae81 100644
> > > > --- a/mm/percpu.c
> > > > +++ b/mm/percpu.c
> > > > @@ -2916,6 +2916,7 @@ static struct pcpu_alloc_info * __init __flatten pcpu_build_alloc_info(
> > > > * Related to atom_size, which could be much larger than the unit_size.
> > > > */
> > > > last_allocs = INT_MAX;
> > > > + best_upa = max_upa;
> > > > for (upa = max_upa; upa; upa--) {
> > > > int allocs = 0, wasted = 0;
> > > > --
> > > > 2.26.3
> > > >
> > > I think the proper fix would be:
> > >
> > > best_upa = 0;
> >
> > I was looking for initializing with something that would work.
> >
>
> I think I prefer setting it to 0 because it forces the loop to have
> succeeded vs being able to bypass it if the for loop logic was changed.
>
> > > for (...) { }
> > > BUG_ON(!best_upa);
> > WARN_ON instead?
>
> This is initialization code. So if upa == 0, it really is a problem.
> Having 0 units per allocation is bogus.
>
> > > upa = best_upa;
> > >
> > > If you're fine with this I'll make the changes and apply it to
> > > for-5.13-fixes.
> > >
> > > Can you also tell me what static analysis tool produced this? I'm just a
> > > little curious because this code hasn't changed in several years so I'd
> > > have expected some static analyzer to have caught this by now.
> >
> > Clang 10
> >
> > Tom
> >
>
> Thanks,
> Dennis
Following up here. Are you find with me making the changes and
attributing it to you? Otherwise I can just spin another patch real
quick.
At this point I've already sent my PR for-5.13-fixes. So I'll queue some
fix for-5.14.
Thanks,
Dennis
^ permalink raw reply [flat|nested] 8+ messages in thread
* Re: [PATCH] percpu: initialize best_upa variable
2021-05-27 20:24 ` Dennis Zhou
@ 2021-05-27 21:09 ` Tom Rix
0 siblings, 0 replies; 8+ messages in thread
From: Tom Rix @ 2021-05-27 21:09 UTC (permalink / raw)
To: Dennis Zhou; +Cc: tj, cl, akpm, linux-mm, linux-kernel
On 5/27/21 1:24 PM, Dennis Zhou wrote:
> Hello,
>
> On Mon, May 17, 2021 at 02:39:21PM +0000, Dennis Zhou wrote:
>> On Mon, May 17, 2021 at 06:17:47AM -0700, Tom Rix wrote:
>>> On 5/16/21 7:05 PM, Dennis Zhou wrote:
>>>> Hello,
>>>>
>>>> On Sat, May 15, 2021 at 11:08:17AM -0700, trix@redhat.com wrote:
>>>>> From: Tom Rix <trix@redhat.com>
>>>>>
>>>>> Static analysis reports this problem
>>>>> percpu.c:2945:6: warning: Assigned value is garbage or undefined
>>>>> upa = best_upa;
>>>>> ^ ~~~~~~~~
>>>>> best_upa may not be set, so initialize it.
>>>>>
>>>>> Signed-off-by: Tom Rix <trix@redhat.com>
>>>>> ---
>>>>> mm/percpu.c | 1 +
>>>>> 1 file changed, 1 insertion(+)
>>>>>
>>>>> diff --git a/mm/percpu.c b/mm/percpu.c
>>>>> index a257c3efdf18b..6578b706fae81 100644
>>>>> --- a/mm/percpu.c
>>>>> +++ b/mm/percpu.c
>>>>> @@ -2916,6 +2916,7 @@ static struct pcpu_alloc_info * __init __flatten pcpu_build_alloc_info(
>>>>> * Related to atom_size, which could be much larger than the unit_size.
>>>>> */
>>>>> last_allocs = INT_MAX;
>>>>> + best_upa = max_upa;
>>>>> for (upa = max_upa; upa; upa--) {
>>>>> int allocs = 0, wasted = 0;
>>>>> --
>>>>> 2.26.3
>>>>>
>>>> I think the proper fix would be:
>>>>
>>>> best_upa = 0;
>>> I was looking for initializing with something that would work.
>>>
>> I think I prefer setting it to 0 because it forces the loop to have
>> succeeded vs being able to bypass it if the for loop logic was changed.
>>
>>>> for (...) { }
>>>> BUG_ON(!best_upa);
>>> WARN_ON instead?
>> This is initialization code. So if upa == 0, it really is a problem.
>> Having 0 units per allocation is bogus.
>>
>>>> upa = best_upa;
>>>>
>>>> If you're fine with this I'll make the changes and apply it to
>>>> for-5.13-fixes.
>>>>
>>>> Can you also tell me what static analysis tool produced this? I'm just a
>>>> little curious because this code hasn't changed in several years so I'd
>>>> have expected some static analyzer to have caught this by now.
>>> Clang 10
>>>
>>> Tom
>>>
>> Thanks,
>> Dennis
> Following up here. Are you find with me making the changes and
> attributing it to you? Otherwise I can just spin another patch real
> quick.
I am fine with you respinning, no need to attribute the change to me.
If you would like a review, include me on the cc.
Thanks!
Tom
> At this point I've already sent my PR for-5.13-fixes. So I'll queue some
> fix for-5.14.
>
> Thanks,
> Dennis
>
^ permalink raw reply [flat|nested] 8+ messages in thread
end of thread, other threads:[~2021-05-27 21:09 UTC | newest]
Thread overview: 8+ messages (download: mbox.gz / follow: Atom feed)
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2021-05-15 18:08 [PATCH] percpu: initialize best_upa variable trix
2021-05-16 23:45 ` Wonhyuk Yang
2021-05-17 2:05 ` Dennis Zhou
2021-05-17 11:06 ` Wonhyuk Yang
2021-05-17 13:17 ` Tom Rix
2021-05-17 14:39 ` Dennis Zhou
2021-05-27 20:24 ` Dennis Zhou
2021-05-27 21:09 ` Tom Rix
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