Messages in this thread | | | Date | Fri, 25 Sep 2015 11:09:13 -0400 | From | Tejun Heo <> | Subject | Re: netlink: Add barrier to netlink_connect for theoretical case |
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Hello, Herbert.
On Fri, Sep 25, 2015 at 11:39:57AM +0800, Herbert Xu wrote: > +static inline bool netlink_bound(struct netlink_sock *nlk) > +{ > + bool bound = READ_ONCE(nlk->bound); > + > + /* Ensure nlk is hashed and visible. */ > + if (bound) > + smp_rmb(); > + > + return bound; > +}
While I can't see anything wrong with the above, I'm not a fan of it for whatever worth that may be. I don't think it adds anything in terms of readability or clarity of the code. It does avoid smp_rmb() when @bound is false but that's unlikely to be helfpul - where the barrier is being avoided is a cold path. This is largely a generic characteristic because if where the barrier is being avoided is a hot path, why wouldn't the code just grab a lock in that path instead of using a gated barrier? So, there's a reason why we don't see code like the above commonly. It doesn't buy us anything meaningful while making the code more complicated and sometimes more fragile.
Thanks.
-- tejun
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