On Mon, Oct 03, 2022 at 12:06:19AM +0200, Frederic Weisbecker wrote: > On Thu, Sep 29, 2022 at 11:07:26AM -0700, Paul E. McKenney wrote: > > This commit adds runtime checks to verify that a given srcu_struct uses > > consistent NMI-safe (or not) read-side primitives on a per-CPU basis. > > > > Link: https://lore.kernel.org/all/20220910221947.171557773@xxxxxxxxxxxxx/ > > > > Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxx> > > Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx> > > Cc: John Ogness <john.ogness@xxxxxxxxxxxxx> > > Cc: Petr Mladek <pmladek@xxxxxxxx> > > --- > > include/linux/srcu.h | 4 ++-- > > include/linux/srcutiny.h | 4 ++-- > > include/linux/srcutree.h | 9 +++++++-- > > kernel/rcu/srcutree.c | 38 ++++++++++++++++++++++++++++++++------ > > 4 files changed, 43 insertions(+), 12 deletions(-) > > > > diff --git a/include/linux/srcu.h b/include/linux/srcu.h > > index 2cc8321c0c86..565f60d57484 100644 > > --- a/include/linux/srcu.h > > +++ b/include/linux/srcu.h > > @@ -180,7 +180,7 @@ static inline int srcu_read_lock_nmisafe(struct srcu_struct *ssp) __acquires(ssp > > int retval; > > > > if (IS_ENABLED(CONFIG_NEED_SRCU_NMI_SAFE)) > > - retval = __srcu_read_lock_nmisafe(ssp); > > + retval = __srcu_read_lock_nmisafe(ssp, true); > > else > > retval = __srcu_read_lock(ssp); > > Shouldn't it be checked also when CONFIG_NEED_SRCU_NMI_SAFE=n ? You are asking why there is no "true" argument to __srcu_read_lock()? That is because it checks unconditionally. OK, so why the "true" argument to __srcu_read_lock_nmisafe(), you ask? Because srcu_gp_start_if_needed() needs to call __srcu_read_lock_nmisafe() while suppressing the checking, which it does by passing in "false". In turn because srcu_gp_start_if_needed() cannot always tell whether its srcu_struct is or is not NMI-safe. Thanx, Paul
