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

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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: Paul E. McKenney <paulmck@kernel.org>
Acked-by: Andrii Nakryiko <andrii@kernel.org>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Uladzislau Rezki (Sony) <urezki@gmail.com>
This commit is contained in:
Paul E. McKenney 2024-10-21 15:09:39 -07:00 committed by Uladzislau Rezki (Sony)
parent fac04efc5c
commit d465492a22
2 changed files with 10 additions and 8 deletions
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15
include/linux/srcu.h
View File

@ -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)
{

3
kernel/rcu/srcutree.c
View File

@ -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)
{