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 <monamagarwal123@xxxxxxxxx>
---
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/20140320150601.GK4405@xxxxxxxxxxxxxxxxxx
Neil
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