On Fri, May 24, 2019 at 06:29:11AM -0700, Paul E. McKenney wrote: > On Fri, May 24, 2019 at 12:36:37PM +0200, Andrea Parri wrote: > > Quoting Paul [1]: > > > > "Given that a quick (and perhaps error-prone) search of the uses > > of rcu_assign_pointer() in v5.1 didn't find a single use of the > > return value, let's please instead change the documentation and > > implementation to eliminate the return value." > > > > [1] https://lkml.kernel.org/r/20190523135013.GL28207@xxxxxxxxxxxxx > > Thank you! A few comments below. Thank you for the suggestions, Paul. > > Thanx, Paul > > > Signed-off-by: Andrea Parri <andrea.parri@xxxxxxxxxxxxxxxxxxxx> > > Cc: "Paul E. McKenney" <paulmck@xxxxxxxxxxxxx> > > Cc: Josh Triplett <josh@xxxxxxxxxxxxxxxx> > > Cc: Steven Rostedt <rostedt@xxxxxxxxxxx> > > Cc: Mathieu Desnoyers <mathieu.desnoyers@xxxxxxxxxxxx> > > Cc: Lai Jiangshan <jiangshanlai@xxxxxxxxx> > > Cc: Joel Fernandes <joel@xxxxxxxxxxxxxxxxx> > > Cc: rcu@xxxxxxxxxxxxxxx > > Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx> > > Cc: Will Deacon <will.deacon@xxxxxxx> > > Cc: Mark Rutland <mark.rutland@xxxxxxx> > > Cc: Matthew Wilcox <willy@xxxxxxxxxxxxx> > > Cc: Sasha Levin <sashal@xxxxxxxxxx> > > --- > > Matthew, Sasha: > > > > The patch is based on -rcu/dev; I took the liberty of applying the > > same change to your #defines in: > > > > tools/testing/radix-tree/linux/rcupdate.h > > tools/include/linux/rcu.h > > > > but I admit that I'm not familiar with their uses: please shout if > > you have any objections with it. > > --- > > Documentation/RCU/whatisRCU.txt | 8 ++++---- > > include/linux/rcupdate.h | 5 ++--- > > tools/include/linux/rcu.h | 11 +++++++++-- > > tools/testing/radix-tree/linux/rcupdate.h | 5 ++++- > > 4 files changed, 19 insertions(+), 10 deletions(-) > > > > diff --git a/Documentation/RCU/whatisRCU.txt b/Documentation/RCU/whatisRCU.txt > > index 981651a8b65d2..f99a87b9a88fa 100644 > > --- a/Documentation/RCU/whatisRCU.txt > > +++ b/Documentation/RCU/whatisRCU.txt > > @@ -212,7 +212,7 @@ synchronize_rcu() > > > > rcu_assign_pointer() > > > > - typeof(p) rcu_assign_pointer(p, typeof(p) v); > > + rcu_assign_pointer(p, typeof(p) v); > > Please add the "void", similar to synchronize_rcu() above. Sure, will do in v2. > > > Yes, rcu_assign_pointer() -is- implemented as a macro, though it > > would be cool to be able to declare a function in this manner. > > @@ -220,9 +220,9 @@ rcu_assign_pointer() > > > > The updater uses this function to assign a new value to an > > RCU-protected pointer, in order to safely communicate the change > > - in value from the updater to the reader. This function returns > > - the new value, and also executes any memory-barrier instructions > > - required for a given CPU architecture. > > + in value from the updater to the reader. This macro does not > > + evaluate to an rvalue, but it does execute any memory-barrier > > + instructions required for a given CPU architecture. > > > > Perhaps just as important, it serves to document (1) which > > pointers are protected by RCU and (2) the point at which a > > diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h > > index 915460ec08722..a5f61a08e65fc 100644 > > --- a/include/linux/rcupdate.h > > +++ b/include/linux/rcupdate.h > > @@ -367,7 +367,7 @@ static inline void rcu_preempt_sleep_check(void) { } > > * other macros that it invokes. > > */ > > #define rcu_assign_pointer(p, v) \ > > -({ \ > > +do { \ > > uintptr_t _r_a_p__v = (uintptr_t)(v); \ > > rcu_check_sparse(p, __rcu); \ > > \ > > @@ -375,8 +375,7 @@ static inline void rcu_preempt_sleep_check(void) { } > > WRITE_ONCE((p), (typeof(p))(_r_a_p__v)); \ > > else \ > > smp_store_release(&p, RCU_INITIALIZER((typeof(p))_r_a_p__v)); \ > > - _r_a_p__v; \ > > -}) > > +} while (0) > > > > /** > > * rcu_swap_protected() - swap an RCU and a regular pointer > > diff --git a/tools/include/linux/rcu.h b/tools/include/linux/rcu.h > > index 7d02527e5bcea..01a435ee48cd6 100644 > > --- a/tools/include/linux/rcu.h > > +++ b/tools/include/linux/rcu.h > > @@ -19,7 +19,14 @@ static inline bool rcu_is_watching(void) > > return false; > > } > > > > -#define rcu_assign_pointer(p, v) ((p) = (v)) > > -#define RCU_INIT_POINTER(p, v) p=(v) > > +#define rcu_assign_pointer(p, v) \ > > +do { \ > > + (p) = (v); \ > > +} while (0) > > + > > +#define RCU_INIT_POINTER(p, v) \ > > +do { \ > > + (p) = (v); \ > > +} while (0) > > These two each fit nicely on one line: > > #define rcu_assign_pointer(p, v) do { (p) = (v); } while (0) > #define RCU_INIT_POINTER(p, v) do { (p) = (v); } while (0) Same here. > > > > > #endif > > diff --git a/tools/testing/radix-tree/linux/rcupdate.h b/tools/testing/radix-tree/linux/rcupdate.h > > index fd280b070fdb1..48212f3a758e6 100644 > > --- a/tools/testing/radix-tree/linux/rcupdate.h > > +++ b/tools/testing/radix-tree/linux/rcupdate.h > > @@ -7,6 +7,9 @@ > > #define rcu_dereference_raw(p) rcu_dereference(p) > > #define rcu_dereference_protected(p, cond) rcu_dereference(p) > > #define rcu_dereference_check(p, cond) rcu_dereference(p) > > -#define RCU_INIT_POINTER(p, v) (p) = (v) > > +#define RCU_INIT_POINTER(p, v) \ > > +do { \ > > + (p) = (v); \ > > +} while (0) > > As does this one. ... And here. Thanks, Andrea
