Commit 9129b017 authored by Andrea Parri's avatar Andrea Parri Committed by Paul E. McKenney
Browse files

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

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: default avatarAndrea 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: default avatarPaul E. McKenney <paulmck@linux.ibm.com>
parent 6da9f775

Documentation/RCU/whatisRCU.txt

+4 −4
Original line number Diff line number Diff line
@@ -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

include/linux/rcupdate.h

+2 −3
Original line number Diff line number Diff line
@@ -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

tools/include/linux/rcu.h

+2 −2
Original line number Diff line number Diff line
@@ -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

tools/testing/radix-tree/linux/rcupdate.h

+1 −1
Original line number Diff line number Diff line
@@ -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

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