On Tue, Oct 22, 2024 at 09:07:17AM +0200, Peter Zijlstra wrote:
> On Mon, Oct 21, 2024 at 08:30:43PM -0700, Paul E. McKenney wrote:
> > Thoughts?
>
> Thanks Paul!
>
> Acked-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
Thank you, Peter! I will apply this on my next rebase.
Thanx, Paul
> > ------------------------------------------------------------------------
> >
> > commit 4433b7d3785d8d2a700f5ed5ca234c64bc63180e
> > Author: Paul E. McKenney <paulmck@xxxxxxxxxx>
> > Date: Mon Oct 21 15:09:39 2024 -0700
> >
> > 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: Paul E. McKenney <paulmck@xxxxxxxxxx>
> > Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
> > Acked-by: Andrii Nakryiko <andrii@xxxxxxxxxx>
> >
> > diff --git a/include/linux/srcu.h b/include/linux/srcu.h
> > index bab1dae3f69e6..512a8c54ba5ba 100644
> > --- a/include/linux/srcu.h
> > +++ b/include/linux/srcu.h
> > @@ -238,13 +238,14 @@ void srcu_check_read_flavor(struct srcu_struct *ssp, int read_flavor);
> > * 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)
> > {
> > diff --git a/kernel/rcu/srcutree.c b/kernel/rcu/srcutree.c
> > index 07147efcb64d3..ae17c214e0de5 100644
> > --- a/kernel/rcu/srcutree.c
> > +++ b/kernel/rcu/srcutree.c
> > @@ -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)
> > {
