Commit d465492a authored by Paul E. McKenney's avatar Paul E. McKenney Committed by Uladzislau Rezki (Sony)
Browse files

srcu: Guarantee non-negative return value from srcu_read_lock() 



For almost 20 years, the int return value from srcu_read_lock() has
been always either zero or one.  This commit therefore documents the
fact that it will be non-negative, and does the same for the underlying
__srcu_read_lock().

[ paulmck: Apply Andrii Nakryiko feedback. ]

Signed-off-by: default avatarPaul E. McKenney <paulmck@kernel.org>
Acked-by: default avatarAndrii Nakryiko <andrii@kernel.org>
Acked-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: default avatarUladzislau Rezki (Sony) <urezki@gmail.com>
parent fac04efc

include/linux/srcu.h

+8 −7
Original line number Diff line number Diff line
@@ -232,13 +232,14 @@ static inline int srcu_read_lock_held(const struct srcu_struct *ssp) 
 * a mutex that is held elsewhere while calling synchronize_srcu() or

 * synchronize_srcu_expedited().

 *

 * The return value from srcu_read_lock() must be passed unaltered

 * to the matching srcu_read_unlock().  Note that srcu_read_lock() and

 * the matching srcu_read_unlock() must occur in the same context, for

 * example, it is illegal to invoke srcu_read_unlock() in an irq handler

 * if the matching srcu_read_lock() was invoked in process context.  Or,

 * for that matter to invoke srcu_read_unlock() from one task and the

 * matching srcu_read_lock() from another.

 * The return value from srcu_read_lock() is guaranteed to be

 * non-negative.  This value must be passed unaltered to the matching

 * srcu_read_unlock().  Note that srcu_read_lock() and the matching

 * srcu_read_unlock() must occur in the same context, for example, it is

 * illegal to invoke srcu_read_unlock() in an irq handler if the matching

 * srcu_read_lock() was invoked in process context.  Or, for that matter to

 * invoke srcu_read_unlock() from one task and the matching srcu_read_lock()

 * from another.

 */

static inline int srcu_read_lock(struct srcu_struct *ssp) __acquires(ssp)

{

kernel/rcu/srcutree.c

+2 −1
Original line number Diff line number Diff line
@@ -738,7 +738,8 @@ EXPORT_SYMBOL_GPL(__srcu_check_read_flavor); 
/*

 * Counts the new reader in the appropriate per-CPU element of the

 * srcu_struct.

 * Returns an index that must be passed to the matching srcu_read_unlock().

 * Returns a guaranteed non-negative index that must be passed to the

 * matching __srcu_read_unlock().

 */

int __srcu_read_lock(struct srcu_struct *ssp)

{