Prev: [PATCH 4/4] workqueue: fix worker management invocation without pending works
Next: pcrypt: sysfs interface
From: Dan Kruchinin on 6 Jul 2010 04:40
On Tue, Jul 6, 2010 at 11:46 AM, Steffen Klassert
<steffen.klassert(a)secunet.com> wrote:
> On Tue, Jul 06, 2010 at 11:40:11AM +0400, Dan Kruchinin wrote:
>> >> >
>> >>
>> >> I think we can use RCU anyway. For instance we could use a structure
>> >>
>> >> struct pcrypt_cpumask {
>> >> � � � cpumask_var_t � � � � � pmask;
>> >> � � � cpumask_var_t � � � � � smask;
>> >> };
>> >>
>> >> and add a pointer to a structure of that type to the instance context.
>> >> Then we could use this pointer for RCU and replace the whole structure
>> >> if a cpumask changes.
>>
>> But is pcrypt interested pmask? If it isn't, pmask field will be unused.
>>
>
> It's probaply not, in this case the struct could look like
>
> struct pcrypt_cpumask {
> � � � �cpumask_var_t � � � � � smask;
> };
>

Would't it be the same as with a pointer to cpumask_var_t? I mean:
struct pcrypt {
...
struct pcrypt_cpumask *mask;
...
} pencrypt;

To assign a pointer via RCU:

int cpumask_change_nitify(...) {
...
struct pcrypt_cpumask *new_mask = kmalloc(sizeof(*mask), GFP);
struct pcrypt_cpumask *old_mask = pencrypt.mask;

if (!new_mask)
error();
if (!alloc_cpumask_var(&new_mask->smask, GFP_KERNEL))
error();

get_serial_cpumask_from_padata(new_mask->mask);
rcu_assign_pointer(pencrypt.mask, new_mask);
synchronize_rcu_bh();

free_cpumask_var(old_mask->smask);
kfree(old_mask);
...
}

It's a bit hard to read this code because at the first sight it
appears unclear and odd why we allocate the structure with only one
member.

--
W.B.R.
Dan Kruchinin
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo(a)vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
From: Steffen Klassert on 6 Jul 2010 09:30
On Tue, Jul 06, 2010 at 12:31:21PM +0400, Dan Kruchinin wrote:
>
> Would't it be the same as with a pointer to cpumask_var_t? I mean:

Using a pointer to cpumask_var_t is a bit problematic because
you don't know a priori about the type of cpumask_var_t.
The type depends whether the cpumasks are on/off stack.
So the easiest thing is to embed it to a struct, then you don't
need to care about the type. If you allocate a struct of type
pcrypt_cpumask you get what you want to have.

> struct pcrypt {
> ...
> struct pcrypt_cpumask *mask;
> ...
> } pencrypt;
>
> To assign a pointer via RCU:
>
> int cpumask_change_nitify(...) {
> ...
> struct pcrypt_cpumask *new_mask = kmalloc(sizeof(*mask), GFP);
> struct pcrypt_cpumask *old_mask = pencrypt.mask;
>
> if (!new_mask)
> error();
> if (!alloc_cpumask_var(&new_mask->smask, GFP_KERNEL))
> error();
>
> get_serial_cpumask_from_padata(new_mask->mask);
> rcu_assign_pointer(pencrypt.mask, new_mask);
> synchronize_rcu_bh();
>
> free_cpumask_var(old_mask->smask);
> kfree(old_mask);
> ...
> }
>
> It's a bit hard to read this code because at the first sight it
> appears unclear and odd why we allocate the structure with only one
> member.
>

We can easily add a code comment if this appears to be unclear :)
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo(a)vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
From: Dan Kruchinin on 6 Jul 2010 12:40
On Tue, Jul 6, 2010 at 5:28 PM, Steffen Klassert
<steffen.klassert(a)secunet.com> wrote:
> On Tue, Jul 06, 2010 at 12:31:21PM +0400, Dan Kruchinin wrote:
>>
>> Would't it be the same as with a pointer to cpumask_var_t? I mean:
>
> Using a pointer to cpumask_var_t is a bit problematic because
> you don't know a priori about the type of cpumask_var_t.
> The type depends whether the cpumasks are on/off stack.
> So the easiest thing is to embed it to a struct, then you don't
> need to care about the type. If you allocate a struct of type
> pcrypt_cpumask you get what you want to have.

Oh, I meant pointer to pointer of course. Anyway you're probably right.
I modified my patches according to the results of our discussion. So
I'm waiting for your fixes.

>
>> struct pcrypt {
>> � ...
>> � struct pcrypt_cpumask *mask;
>> � ...
>> } pencrypt;
>>
>> To assign a pointer via RCU:
>>
>> int cpumask_change_nitify(...) {
>> � �...
>> � struct pcrypt_cpumask *new_mask = kmalloc(sizeof(*mask), GFP);
>> � struct pcrypt_cpumask *old_mask = pencrypt.mask;
>>
>> � if (!new_mask)
>> � � �error();
>> � if (!alloc_cpumask_var(&new_mask->smask, GFP_KERNEL))
>> � � �error();
>>
>> � get_serial_cpumask_from_padata(new_mask->mask);
>> � rcu_assign_pointer(pencrypt.mask, new_mask);
>> � synchronize_rcu_bh();
>>
>> � free_cpumask_var(old_mask->smask);
>> � kfree(old_mask);
>> � ...
>> }
>>
>> It's a bit hard to read this code because at the first sight it
>> appears unclear and odd why we allocate the structure with only one
>> member.
>>
>
> We can easily add a code comment if this appears to be unclear :)
>



--
W.B.R.
Dan Kruchinin
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo(a)vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
From: Steffen Klassert on 7 Jul 2010 09:20
On Tue, Jul 06, 2010 at 08:30:40PM +0400, Dan Kruchinin wrote:
>
> I modified my patches according to the results of our discussion. So
> I'm waiting for your fixes.
>

I'll send out a patchset later. The first three patches of the patchset
address the empty padata cpumask handling. I did some rough tests and it
appeared to work. However, I still have no fixed testcase for this. So see
whether this works with your patches and whether it meets your requirements.
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo(a)vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
First  |  Prev  | 
Pages: 1 2 3
Prev: [PATCH 4/4] workqueue: fix worker management invocation without pending works
Next: pcrypt: sysfs interface