On Mon, Oct 21, 2024 at 04:50:44PM -0700, Andrii Nakryiko wrote: > On Mon, Oct 21, 2024 at 3:13 PM Paul E. McKenney <paulmck@xxxxxxxxxx> wrote: > > > > 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. > > > > Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxx> > > Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx> > > Cc: 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. > > For uprobe work I'm using __srcu_read_lock() and __srcu_read_unlock(). > Presumably the same non-negative index will be returned/consumed there > as well, right? Can we add a blurb to that effect for them as well? Does the change shown below cover it? > Otherwise LGTM, thanks! > > Acked-by: Andrii Nakryiko <andrii@xxxxxxxxxx> Thank you -- I will apply on my next rebase. Thanx, Paul > > */ > > 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..3d587bf2b2c12 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) {