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Date: Thu, 14 Feb 2008 09:24:27 -0800 From: Randy Dunlap <randy.dunlap@...cle.com> To: paulmck@...ux.vnet.ibm.com Cc: linux-kernel@...r.kernel.org, shemminger@...tta.com, davem@...emloft.net, netdev@...r.kernel.org, dipankar@...ibm.com, ego@...ibm.com, herbert@...dor.apana.org.au, akpm@...ux-foundation.org Subject: Re: [PATCH 2/2] add rcu_assign_index() if ever needed On Wed, 13 Feb 2008 14:05:15 -0800 Paul E. McKenney wrote: > Hello again! > > This is a speculative patch that as far as I can tell is not yet required. > If anyone applies RCU to a data structure allocated out of an array, using > array indexes in place of pointers to link the array elements together, > then the rcu_assign_index() function in this patch will be needed to > assign a given element's array index to the RCU-traversed index. The > implementation is exactly that of the old rcu_assign_pointer(), so is > extremely well tested. > > The existing rcu_assign_pointer() will emit a compiler warning in cases > where rcu_assign_index() is required. > > Signed-off-by: Paul E. McKenney <paulmck@...ux.vnet.ibm.com> > --- > > rcupdate.h | 18 ++++++++++++++++++ > 1 file changed, 18 insertions(+) > > diff -urpNa -X dontdiff linux-2.6.24-rap/include/linux/rcupdate.h linux-2.6.24-rai/include/linux/rcupdate.h > --- linux-2.6.24-rap/include/linux/rcupdate.h 2008-02-13 13:36:47.000000000 -0800 > +++ linux-2.6.24-rai/include/linux/rcupdate.h 2008-02-13 10:55:40.000000000 -0800 > @@ -286,6 +286,24 @@ extern struct lockdep_map rcu_lock_map; > }) > > /** > + * rcu_assign_index - assign (publicize) a index of a newly > + * initialized array elementg that will be dereferenced by RCU > + * read-side critical sections. Returns the value assigned. > + * > + * Inserts memory barriers on architectures that require them > + * (pretty much all of them other than x86), and also prevents > + * the compiler from reordering the code that initializes the > + * structure after the index assignment. More importantly, this > + * call documents which indexes will be dereferenced by RCU read-side > + * code. > + */ s/a index/index/ Along with Gautham's typo fix, you could also make this be passable kernel-doc notation. :) See Documentation/kernel-doc-nano-HOWTO.txt for details. Summary: The function (or macro) name and short description must be on one line. This is followed by the parameters, then a "blank" (actually " *") line, then any (longer) description, notes, etc. So basically: /** * rcu_assign_index - assign (publicize) index of a newly initialized array element * @p: description of @p * @v: description of @v * * This function assigns (publicizes) the index of a newly * initialized array element that will be dereferenced by RCU * read-side critical sections. Returns the value assigned. * * Inserts memory barriers on architectures that require them * (pretty much all of them other than x86), and also prevents * the compiler from reordering the code that initializes the * structure after the index assignment. More importantly, this * call documents which indexes will be dereferenced by RCU read-side * code. */ > + > +#define rcu_assign_index(p, v) ({ \ > + smp_wmb(); \ > + (p) = (v); \ > + }) > + > +/** > * synchronize_sched - block until all CPUs have exited any non-preemptive > * kernel code sequences. > * --- ~Randy -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
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