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SubjectRe: [PATCH] net/core: Use RCU_INIT_POINTER(x, NULL) in netpoll.c
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
>
>


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