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Date: Mon, 24 Mar 2014 13:03:29 +0100 From: Arend van Spriel <arend@...adcom.com> To: Neil Horman <nhorman@...driver.com>, Monam Agarwal <monamagarwal123@...il.com> CC: <rcj@...ux.vnet.ibm.com>, <mhcerri@...ux.vnet.ibm.com>, <fin@...ux.vnet.ibm.com>, <herbert@...dor.apana.org.au>, <davem@...emloft.net>, <linux-crypto@...r.kernel.org>, <linux-kernel@...r.kernel.org> Subject: Re: [PATCH] drivers/crypto: Use RCU_INIT_POINTER(x, NULL) in nx/nx-842.c 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@...il.com> >> --- >> 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@linux.vnet.ibm.com > > Neil > >> -- >> 1.7.9.5 >> >> -- >> To unsubscribe from this list: send the line "unsubscribe linux-crypto" in >> the body of a message to majordomo@...r.kernel.org >> More majordomo info at http://vger.kernel.org/majordomo-info.html >> > -- > To unsubscribe from this list: send the line "unsubscribe linux-kernel" in > the body of a message to majordomo@...r.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html > Please read the FAQ at http://www.tux.org/lkml/ > -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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