On Mon, Oct 03, 2022 at 06:32:10AM -0700, Paul E. McKenney wrote: > On Mon, Oct 03, 2022 at 02:37:21PM +0200, Frederic Weisbecker wrote: > > On Mon, Oct 03, 2022 at 04:57:18AM -0700, Paul E. McKenney wrote: > > > On Mon, Oct 03, 2022 at 12:13:31PM +0200, Frederic Weisbecker wrote: > > > > On Sun, Oct 02, 2022 at 04:51:03PM -0700, Paul E. McKenney wrote: > > > > > 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. > > > > > > > > It checks unconditionally but it always assumes not to be called as nmisafe. > > > > > > > > For example on x86/arm64/loongarch, the same ssp used with both srcu_read_lock() and > > > > srcu_read_lock_nmisafe() won't report an issue. But on powerpc it will. > > > > > > > > My point is that strong archs should warn as well on behalf of others, to detect > > > > mistakes early. > > > > > > Good point, especially given that x86_64 and arm64 are a rather large > > > fraction of the uses. Not critically urgent, but definitely nice to have. > > > > No indeed. > > > > > > > > Did you by chance have a suggestion for a nice way to accomplish this? > > > > This could be like this: > > > > enum srcu_nmi_flags { > > SRCU_NMI_UNKNOWN = 0x0, > > SRCU_NMI_UNSAFE = 0x1, > > SRCU_NMI_SAFE = 0x2 > > }; > > > > #ifdef CONFIG_NEED_SRCU_NMI_SAFE > > static inline int __srcu_read_lock_nmisafe(struct srcu_struct *ssp, enum srcu_nmi_flags flags) > > { > > int idx; > > struct srcu_data *sdp = raw_cpu_ptr(ssp->sda); > > > > idx = READ_ONCE(ssp->srcu_idx) & 0x1; > > atomic_long_inc(&sdp->srcu_lock_count[idx]); > > smp_mb__after_atomic(); /* B */ /* Avoid leaking the critical section. */ > > > > srcu_check_nmi_safety(ssp, flags); > > > > return idx; > > } > > #else > > static inline int __srcu_read_lock_nmisafe(struct srcu_struct *ssp, enum srcu_nmi_flags flags) > > { > > srcu_check_nmi_safety(ssp, flags); > > return __srcu_read_lock(ssp); > > } > > #endif > > > > static inline int srcu_read_lock_nmisafe(struct srcu_struct *ssp) > > { > > return __srcu_read_lock_nmisafe(ssp, SRCU_NMI_SAFE); > > } > > > > // An __srcu_read_lock() caller in kernel/rcu/tasks.h must be > > // taken care of as well > > static inline int srcu_read_lock(struct srcu_struct *ssp) > > { > > srcu_check_nmi_safety(ssp, SRCU_NMI_UNSAFE); > > return __srcu_read_lock(ssp); > > } > > > > And then you can call __srcu_read_lock_nmisafe(ssp, SRCU_NMI_UNKNOWN) from > > initializers of gp. > > Not bad at all! > > Would you like to send a patch? > > I do not consider this to be something for the current merge window even > if the rest goes in because printk() is used heavily and because it is > easy to get access to powerpc and presumably also riscv systems. > > But as you say, it would be very good to have longer term for the case > where srcu_read_lock_nmisafe() is used for some more obscure purpose. Sure thing! Thanks.
