This patch replaces rcu_assign_pointer(x, NULL) with RCU_INIT_POINTER(x, NULL)
The rcu_assign_pointer() ensures that the initialization of a structure
is carried out before storing a pointer to that structure.
And in the case of the NULL pointer, there is no structure to initialize.
So, rcu_assign_pointer(p, NULL) can be safely converted to RCU_INIT_POINTER(p, NULL)
Signed-off-by: Monam Agarwal <[email protected]>
---
drivers/crypto/nx/nx-842.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)
diff --git a/drivers/crypto/nx/nx-842.c b/drivers/crypto/nx/nx-842.c
index 1e5481d..c4fcbf4 100644
--- a/drivers/crypto/nx/nx-842.c
+++ b/drivers/crypto/nx/nx-842.c
@@ -1234,7 +1234,7 @@ static int __exit nx842_remove(struct vio_dev *viodev)
old_devdata = rcu_dereference_check(devdata,
lockdep_is_held(&devdata_mutex));
of_reconfig_notifier_unregister(&nx842_of_nb);
- rcu_assign_pointer(devdata, NULL);
+ RCU_INIT_POINTER(devdata, NULL);
spin_unlock_irqrestore(&devdata_mutex, flags);
synchronize_rcu();
dev_set_drvdata(&viodev->dev, NULL);
@@ -1285,7 +1285,7 @@ static void __exit nx842_exit(void)
spin_lock_irqsave(&devdata_mutex, flags);
old_devdata = rcu_dereference_check(devdata,
lockdep_is_held(&devdata_mutex));
- rcu_assign_pointer(devdata, NULL);
+ RCU_INIT_POINTER(devdata, NULL);
spin_unlock_irqrestore(&devdata_mutex, flags);
synchronize_rcu();
if (old_devdata)
--
1.7.9.5
On Mon, Mar 24, 2014 at 01:01:04AM +0530, Monam Agarwal wrote:
> This patch replaces rcu_assign_pointer(x, NULL) with RCU_INIT_POINTER(x, NULL)
>
> The rcu_assign_pointer() ensures that the initialization of a structure
> is carried out before storing a pointer to that structure.
> And in the case of the NULL pointer, there is no structure to initialize.
> So, rcu_assign_pointer(p, NULL) can be safely converted to RCU_INIT_POINTER(p, NULL)
>
> Signed-off-by: Monam Agarwal <[email protected]>
> ---
> drivers/crypto/nx/nx-842.c | 4 ++--
> 1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/crypto/nx/nx-842.c b/drivers/crypto/nx/nx-842.c
> index 1e5481d..c4fcbf4 100644
> --- a/drivers/crypto/nx/nx-842.c
> +++ b/drivers/crypto/nx/nx-842.c
> @@ -1234,7 +1234,7 @@ static int __exit nx842_remove(struct vio_dev *viodev)
> old_devdata = rcu_dereference_check(devdata,
> lockdep_is_held(&devdata_mutex));
> of_reconfig_notifier_unregister(&nx842_of_nb);
> - rcu_assign_pointer(devdata, NULL);
> + RCU_INIT_POINTER(devdata, NULL);
> spin_unlock_irqrestore(&devdata_mutex, flags);
> synchronize_rcu();
> dev_set_drvdata(&viodev->dev, NULL);
> @@ -1285,7 +1285,7 @@ static void __exit nx842_exit(void)
> spin_lock_irqsave(&devdata_mutex, flags);
> old_devdata = rcu_dereference_check(devdata,
> lockdep_is_held(&devdata_mutex));
> - rcu_assign_pointer(devdata, NULL);
> + RCU_INIT_POINTER(devdata, NULL);
> spin_unlock_irqrestore(&devdata_mutex, flags);
> synchronize_rcu();
> if (old_devdata)
This really does't seem right. rcu_assign_pointer users ACCESS_ONCE to protect
against multiple loads that allow for concurrent read/write use with parallel
rcu_dereference calls, whereas RCU_INIT_POINTER does not. It also just doesn't
look right. We've already initalized the pointerin nx842_init, we don't need to
re-initalize it here, we need to assign it to NULL.
Neil
> --
> 1.7.9.5
>
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>
On 24/03/14 12:16, Neil Horman wrote:
> On Mon, Mar 24, 2014 at 01:01:04AM +0530, Monam Agarwal wrote:
>> This patch replaces rcu_assign_pointer(x, NULL) with RCU_INIT_POINTER(x, NULL)
>>
>> The rcu_assign_pointer() ensures that the initialization of a structure
>> is carried out before storing a pointer to that structure.
>> And in the case of the NULL pointer, there is no structure to initialize.
>> So, rcu_assign_pointer(p, NULL) can be safely converted to RCU_INIT_POINTER(p, NULL)
>>
>> Signed-off-by: Monam Agarwal <[email protected]>
>> ---
>> drivers/crypto/nx/nx-842.c | 4 ++--
>> 1 file changed, 2 insertions(+), 2 deletions(-)
>>
>> diff --git a/drivers/crypto/nx/nx-842.c b/drivers/crypto/nx/nx-842.c
>> index 1e5481d..c4fcbf4 100644
>> --- a/drivers/crypto/nx/nx-842.c
>> +++ b/drivers/crypto/nx/nx-842.c
>> @@ -1234,7 +1234,7 @@ static int __exit nx842_remove(struct vio_dev *viodev)
>> old_devdata = rcu_dereference_check(devdata,
>> lockdep_is_held(&devdata_mutex));
>> of_reconfig_notifier_unregister(&nx842_of_nb);
>> - rcu_assign_pointer(devdata, NULL);
>> + RCU_INIT_POINTER(devdata, NULL);
>> spin_unlock_irqrestore(&devdata_mutex, flags);
>> synchronize_rcu();
>> dev_set_drvdata(&viodev->dev, NULL);
>> @@ -1285,7 +1285,7 @@ static void __exit nx842_exit(void)
>> spin_lock_irqsave(&devdata_mutex, flags);
>> old_devdata = rcu_dereference_check(devdata,
>> lockdep_is_held(&devdata_mutex));
>> - rcu_assign_pointer(devdata, NULL);
>> + RCU_INIT_POINTER(devdata, NULL);
>> spin_unlock_irqrestore(&devdata_mutex, flags);
>> synchronize_rcu();
>> if (old_devdata)
>
> This really does't seem right. rcu_assign_pointer users ACCESS_ONCE to protect
> against multiple loads that allow for concurrent read/write use with parallel
> rcu_dereference calls, whereas RCU_INIT_POINTER does not. It also just doesn't
> look right. We've already initalized the pointerin nx842_init, we don't need to
> re-initalize it here, we need to assign it to NULL.
I was being cautious as well, but Paul gave me an explanation [1]
Hope it helps you as well ;-)
But I think I also saw a patch that modifies rcu_assign_pointer to
handle NULL assignment. Don't recall the thread.
Regards,
Arend
[1] http://mid.gmane.org/[email protected]
>
> Neil
>
>> --
>> 1.7.9.5
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>>
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