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rcu: Don't return a value from rcu_assign_pointer()

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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@linux.ibm.com

Signed-off-by: Andrea Parri <andrea.parri@amarulasolutions.com>
Cc: "Paul E. McKenney" <paulmck@linux.ibm.com>
Cc: Josh Triplett <josh@joshtriplett.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: Lai Jiangshan <jiangshanlai@gmail.com>
Cc: Joel Fernandes <joel@joelfernandes.org>
Cc: rcu@vger.kernel.org
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Will Deacon <will.deacon@arm.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Sasha Levin <sashal@kernel.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.ibm.com>
This commit is contained in:
Andrea Parri 2019-05-27 10:49:57 +02:00 committed by Paul E. McKenney
parent 6da9f77517
commit 9129b017b5
4 changed files with 9 additions and 10 deletions
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8
Documentation/RCU/whatisRCU.txt
View File

@ -212,7 +212,7 @@ synchronize_rcu()
rcu_assign_pointer()
typeof(p) rcu_assign_pointer(p, typeof(p) v);
void rcu_assign_pointer(p, typeof(p) v);
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

5
include/linux/rcupdate.h
View File

@ -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

4
tools/include/linux/rcu.h
View File

@ -19,7 +19,7 @@ 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)
#endif

2
tools/testing/radix-tree/linux/rcupdate.h
View File

@ -7,6 +7,6 @@
#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)
#endif