| Message ID | 1395601966-12490-1-git-send-email-monamagarwal123@gmail.com |
|---|---|
| State | Accepted, archived |
| Delegated to: | David Miller |
| Headers | show |
On Mon, Mar 24, 2014 at 12:42:46AM +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@gmail.com> No, I don't think this is right. __netpoll_cleanup can be called in parallel with bottom half access to dev->npinfo. rcu_assign pointer is safe against those accesses, but RCU_INIT_POINTER is not. Neil > --- > net/core/netpoll.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/net/core/netpoll.c b/net/core/netpoll.c > index 7291dde..41c4e9c 100644 > --- a/net/core/netpoll.c > +++ b/net/core/netpoll.c > @@ -809,7 +809,7 @@ void __netpoll_cleanup(struct netpoll *np) > if (ops->ndo_netpoll_cleanup) > ops->ndo_netpoll_cleanup(np->dev); > > - rcu_assign_pointer(np->dev->npinfo, NULL); > + RCU_INIT_POINTER(np->dev->npinfo, NULL); > call_rcu_bh(&npinfo->rcu, rcu_cleanup_netpoll_info); > } > } > -- > 1.7.9.5 > > -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
On Mon, 2014-03-24 at 07:11 -0400, Neil Horman wrote: > On Mon, Mar 24, 2014 at 12:42:46AM +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@gmail.com> > No, I don't think this is right. __netpoll_cleanup can be called in parallel > with bottom half access to dev->npinfo. rcu_assign pointer is safe against > those accesses, but RCU_INIT_POINTER is not. Wow, it is always safe for NULL value. -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
On Mon, Mar 24, 2014 at 06:14:35AM -0700, Eric Dumazet wrote: > On Mon, 2014-03-24 at 07:11 -0400, Neil Horman wrote: > > On Mon, Mar 24, 2014 at 12:42:46AM +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@gmail.com> > > No, I don't think this is right. __netpoll_cleanup can be called in parallel > > with bottom half access to dev->npinfo. rcu_assign pointer is safe against > > those accesses, but RCU_INIT_POINTER is not. > > Wow, it is always safe for NULL value. > Ok, After reading Paul's explination of what this is doing: http://mid.gmane.org/20140320150601.GK4405@linux.vnet.ibm.com This makes a bit more sense to me, and I see that its safe, but I'm still not sure that I like it, just from a readability standpoint. Making the conversion removes a memory barrier and the use of a volatile variable, but this isn't a hot path, and the use of rcu_assign_pointer seems more readable to me as its balanced with the rcu_assign_pointer in __netpoll_setup. Doesn't seem worth the tradeoff to me. Neil -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
From: Monam Agarwal <monamagarwal123@gmail.com> Date: Mon, 24 Mar 2014 00:42:46 +0530 > 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@gmail.com> Applied. -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
On Mon, Mar 24, 2014 at 07:11:44AM -0400, Neil Horman wrote: > On Mon, Mar 24, 2014 at 12:42:46AM +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@gmail.com> > No, I don't think this is right. __netpoll_cleanup can be called in parallel > with bottom half access to dev->npinfo. rcu_assign pointer is safe against > those accesses, but RCU_INIT_POINTER is not. Hello, Neil, But in this case, NULL is being assigned, so there should be no problem. If this was a non-NULL pointer to a structure that had not already been exposed to readers, then yes, this would be a problem. But NULL pointers are OK to assign using RCU_INIT_POINTER(). Thanx, Paul > Neil > > > --- > > net/core/netpoll.c | 2 +- > > 1 file changed, 1 insertion(+), 1 deletion(-) > > > > diff --git a/net/core/netpoll.c b/net/core/netpoll.c > > index 7291dde..41c4e9c 100644 > > --- a/net/core/netpoll.c > > +++ b/net/core/netpoll.c > > @@ -809,7 +809,7 @@ void __netpoll_cleanup(struct netpoll *np) > > if (ops->ndo_netpoll_cleanup) > > ops->ndo_netpoll_cleanup(np->dev); > > > > - rcu_assign_pointer(np->dev->npinfo, NULL); > > + RCU_INIT_POINTER(np->dev->npinfo, NULL); > > call_rcu_bh(&npinfo->rcu, rcu_cleanup_netpoll_info); > > } > > } > > -- > > 1.7.9.5 > > > > > -- > To unsubscribe from this list: send the line "unsubscribe linux-kernel" in > the body of a message to majordomo@vger.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 netdev" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
diff --git a/net/core/netpoll.c b/net/core/netpoll.c index 7291dde..41c4e9c 100644 --- a/net/core/netpoll.c +++ b/net/core/netpoll.c @@ -809,7 +809,7 @@ void __netpoll_cleanup(struct netpoll *np) if (ops->ndo_netpoll_cleanup) ops->ndo_netpoll_cleanup(np->dev); - rcu_assign_pointer(np->dev->npinfo, NULL); + RCU_INIT_POINTER(np->dev->npinfo, NULL); call_rcu_bh(&npinfo->rcu, rcu_cleanup_netpoll_info); } }
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@gmail.com> --- net/core/netpoll.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)