Hi Paul, Minor nitpicks in kernel-doc comment of srcu_read_lock_fast_updown().
On Sun, 2 Nov 2025 13:44:32 -0800, Paul E. McKenney wrote: > This commit creates an SRCU-fast-updown API, including > DEFINE_SRCU_FAST_UPDOWN(), DEFINE_STATIC_SRCU_FAST_UPDOWN(), > __init_srcu_struct_fast_updown(), init_srcu_struct_fast_updown(), > srcu_read_lock_fast_updown(), srcu_read_unlock_fast_updown(), > __srcu_read_lock_fast_updown(), and __srcu_read_unlock_fast_updown(). > > These are initially identical to their SRCU-fast counterparts, but both > SRCU-fast and SRCU-fast-updown will be optimized in different directions > by later commits. SRCU-fast will lack any sort of srcu_down_read() and > srcu_up_read() APIs, which will enable extremely efficient NMI safety. > For its part, SRCU-fast-updown will not be NMI safe, which will enable > reasonably efficient implementations of srcu_down_read_fast() and > srcu_up_read_fast(). > > Signed-off-by: Paul E. McKenney <[email protected]> > Cc: Andrii Nakryiko <[email protected]> > Cc: Alexei Starovoitov <[email protected]> > Cc: Peter Zijlstra <[email protected]> > Cc: <[email protected]> > --- > include/linux/srcu.h | 77 +++++++++++++++++++++++++++++++++++++--- > include/linux/srcutiny.h | 16 +++++++++ > include/linux/srcutree.h | 55 ++++++++++++++++++++++++++-- > kernel/rcu/srcutree.c | 39 +++++++++++++++++--- > 4 files changed, 176 insertions(+), 11 deletions(-) > > diff --git a/include/linux/srcu.h b/include/linux/srcu.h > index 1dd6812aabe7..1fbf475eae5e 100644 > --- a/include/linux/srcu.h > +++ b/include/linux/srcu.h [...] > @@ -305,6 +315,46 @@ static inline struct srcu_ctr __percpu > *srcu_read_lock_fast(struct srcu_struct * > return retval; > } > > +/** > + * srcu_read_lock_fast_updown - register a new reader for an > SRCU-fast-updown structure. > + * @ssp: srcu_struct in which to register the new reader. > + * > + * Enter an SRCU read-side critical section, but for a light-weight > + * smp_mb()-free reader. See srcu_read_lock() for more information. > + * This function is compatible with srcu_down_read_fast(), but is not > + * NMI-safe. > + * > + * For srcu_read_lock_fast_updown() to be used on an srcu_struct > + * structure, that structure must have been defined using either > + * DEFINE_SRCU_FAST_UPDOWN() or DEFINE_STATIC_SRCU_FAST_UPDOWN() on the one > + * hand or initialized with init_srcu_struct_fast_updown() on the other. > + * Such an srcu_struct structure cannot be passed to any non-fast-updown > + * variant of srcu_read_{,un}lock() or srcu_{down,up}_read(). In kernels > + * built with CONFIG_PROVE_RCU=y, () will complain bitterly if you ignore > + * this * restriction. Probably, * built with CONFIG_PROVE_RCU=y, __srcu_check_read_flavor() will complain * bitterly if you ignore this restriction. ?? > + * > + * Grace-period auto-expediting is disabled for SRCU-fast-updown > + * srcu_struct structures because SRCU-fast-updown expedited grace periods > + * invoke synchronize_rcu_expedited(), IPIs and all. If you need expedited > + * SRCU-fast-updown grace periods, use synchronize_srcu_expedited(). > + * > + * The srcu_read_lock_fast_updown() function can be invoked only from > + those contexts where RCU is watching, that is, from contexts where > + it would be legal to invoke rcu_read_lock(). Otherwise, lockdep will > + complain. kernel-doc (script) complains: Warning: include/linux/srcu.h:341 bad line: those contexts where RCU is watching, that is, from contexts where Warning: include/linux/srcu.h:342 bad line: it would be legal to invoke rcu_read_lock(). Otherwise, lockdep will Warning: include/linux/srcu.h:343 bad line: complain. Leading "* "s are missing. Thanks, Akira > + */ > +static inline struct srcu_ctr __percpu *srcu_read_lock_fast_updown(struct > srcu_struct *ssp) > +__acquires(ssp) > +{ > + struct srcu_ctr __percpu *retval; > + > + RCU_LOCKDEP_WARN(!rcu_is_watching(), "RCU must be watching > srcu_read_lock_fast_updown()."); > + srcu_check_read_flavor(ssp, SRCU_READ_FLAVOR_FAST_UPDOWN); > + retval = __srcu_read_lock_fast_updown(ssp); > + rcu_try_lock_acquire(&ssp->dep_map); > + return retval; > +} > + > /* > * Used by tracing, cannot be traced and cannot call lockdep. > * See srcu_read_lock_fast() for more information. [...]
