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 <monamagarwal...@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.gk4...@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 linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
