>
> On Fri, Jan 03, 2025 at 01:50:50PM +0800, Z qiang wrote:
> > >
> > > On Thu, Jan 02, 2025 at 01:41:16PM +0800, Oliver Sang wrote:
> > > > hi, Zqiang, hi, Paul,
> > > >
> > > > On Tue, Dec 31, 2024 at 08:19:44AM -0800, Paul E. McKenney wrote:
> > > > > On Tue, Dec 31, 2024 at 03:16:25PM +0800, Z qiang wrote:
> > > >
> > > > [...]
> > > >
> > > > > > >
> > > > > > > If you fix the issue in a separate patch/commit (i.e. not just a
> > > > > > > new version of
> > > > > > > the same patch/commit), kindly add following tags
> > > > > > > | Reported-by: kernel test robot <[email protected]>
> > > > > > > | Closes:
> > > > > > > https://lore.kernel.org/oe-lkp/[email protected]
> > > > > > >
> > > > > >
> > > > > > Please try the following modifications:
> > > >
> > > > yes, the following modifications fix the issues we found for
> > > > 9216c28c6a. thanks!
> > > >
> > > > Tested-by: kernel test robot <[email protected]>
> > >
> > > Thank you, and I will apply this during my next rebase.
> > >
> > > Zqiang, unless you tell me otherwise, I will add your Co-developed-by
> > > and Signed-off-by.
> > >
> > > Either way, Happy Square New Year!
> >
> > Thank you, Happy New Year! :)
>
> And here you go! Please let me know of anything I missed.
>
> And thank you for saving me the time it would have taken to track
> this one down. ;-)
>
> Thanx, Paul
>
> ------------------------------------------------------------------------
>
> commit 71c893e6d1857d1e4ea37aec557d734a560fdb39
> Author: Paul E. McKenney <[email protected]>
> Date: Thu Dec 19 16:08:54 2024 -0800
>
> srcu: Make SRCU readers use ->srcu_ctrs for counter selection
>
> This commit causes SRCU readers to use ->srcu_ctrs for counter
> selection instead of ->srcu_idx. This takes another step towards
> array-indexing-free SRCU readers.
>
> [ paulmck: Apply kernel test robot feedback. ]
>
> Co-developed-by: Z qiang <[email protected]>
> Signed-off-by: Z qiang <[email protected]>
> Signed-off-by: Paul E. McKenney <[email protected]>
> Tested-by: kernel test robot <[email protected]>
>
> diff --git a/include/linux/srcutree.h b/include/linux/srcutree.h
> index c794d599db5c1..1b01ced61a45b 100644
> --- a/include/linux/srcutree.h
> +++ b/include/linux/srcutree.h
> @@ -101,6 +101,7 @@ struct srcu_usage {
> */
> struct srcu_struct {
> unsigned int srcu_idx; /* Current rdr array element.
> */
> + struct srcu_ctr __percpu *srcu_ctrp;
> struct srcu_data __percpu *sda; /* Per-CPU srcu_data array. */
> struct lockdep_map dep_map;
> struct srcu_usage *srcu_sup; /* Update-side data. */
> @@ -167,6 +168,7 @@ struct srcu_struct {
> #define __SRCU_STRUCT_INIT(name, usage_name, pcpu_name)
> \
> {
> \
> .sda = &pcpu_name,
> \
> + .srcu_ctrp = &pcpu_name.srcu_ctrs[0],
> \
> __SRCU_STRUCT_INIT_COMMON(name, usage_name)
> \
> }
>
> @@ -222,13 +224,12 @@ void srcu_torture_stats_print(struct srcu_struct *ssp,
> char *tt, char *tf);
> */
> static inline int __srcu_read_lock_lite(struct srcu_struct *ssp)
> {
> - int idx;
> + struct srcu_ctr __percpu *scp = READ_ONCE(ssp->srcu_ctrp);
>
> RCU_LOCKDEP_WARN(!rcu_is_watching(), "RCU must be watching
> srcu_read_lock_lite().");
> - idx = READ_ONCE(ssp->srcu_idx) & 0x1;
> - this_cpu_inc(ssp->sda->srcu_ctrs[idx].srcu_locks.counter); /* Y */
> + this_cpu_inc(scp->srcu_locks.counter); /* Y */
> barrier(); /* Avoid leaking the critical section. */
> - return idx;
> + return scp - &ssp->sda->srcu_ctrs[0];
> }
>
> /*
> diff --git a/kernel/rcu/srcutree.c b/kernel/rcu/srcutree.c
> index d7ee2f345e192..3bf7f41ad72b8 100644
> --- a/kernel/rcu/srcutree.c
> +++ b/kernel/rcu/srcutree.c
> @@ -253,8 +253,10 @@ static int init_srcu_struct_fields(struct srcu_struct
> *ssp, bool is_static)
> atomic_set(&ssp->srcu_sup->srcu_barrier_cpu_cnt, 0);
> INIT_DELAYED_WORK(&ssp->srcu_sup->work, process_srcu);
> ssp->srcu_sup->sda_is_static = is_static;
> - if (!is_static)
> + if (!is_static) {
> ssp->sda = alloc_percpu(struct srcu_data);
> + ssp->srcu_ctrp = &ssp->sda->srcu_ctrs[0];
> + }
> if (!ssp->sda)
> goto err_free_sup;
ssp->srcu_ctrp should be assigned a value under the condition that
ssp->sda is allocated successfully.
- if (!is_static) {
+ if (!is_static)
ssp->sda = alloc_percpu(struct srcu_data);
- ssp->srcu_ctrp = &ssp->sda->srcu_ctrs[0];
- }
if (!ssp->sda)
goto err_free_sup;
+ if (!is_static)
+ ssp->srcu_ctrp = &ssp->sda->srcu_ctrs[0];
> init_srcu_struct_data(ssp);
> @@ -742,12 +744,11 @@ EXPORT_SYMBOL_GPL(__srcu_check_read_flavor);
> */
> int __srcu_read_lock(struct srcu_struct *ssp)
> {
> - int idx;
> + struct srcu_ctr __percpu *scp = READ_ONCE(ssp->srcu_ctrp);
>
> - idx = READ_ONCE(ssp->srcu_idx) & 0x1;
> - this_cpu_inc(ssp->sda->srcu_ctrs[idx].srcu_locks.counter);
> + this_cpu_inc(scp->srcu_locks.counter);
> smp_mb(); /* B */ /* Avoid leaking the critical section. */
> - return idx;
> + return scp - &ssp->sda->srcu_ctrs[0];
> }
> EXPORT_SYMBOL_GPL(__srcu_read_lock);
>
> @@ -772,13 +773,11 @@ EXPORT_SYMBOL_GPL(__srcu_read_unlock);
> */
> int __srcu_read_lock_nmisafe(struct srcu_struct *ssp)
> {
> - int idx;
> - struct srcu_data *sdp = raw_cpu_ptr(ssp->sda);
> + struct srcu_ctr __percpu *scp = READ_ONCE(ssp->srcu_ctrp);
Should this be the case?
struct srcu_ctr *scp = raw_cpu_ptr(ssp->srcu_ctrp);
>
> - idx = READ_ONCE(ssp->srcu_idx) & 0x1;
> - atomic_long_inc(&sdp->srcu_ctrs[idx].srcu_locks);
> + atomic_long_inc(&scp->srcu_locks);
> smp_mb__after_atomic(); /* B */ /* Avoid leaking the critical
> section. */
> - return idx;
> + return scp - &ssp->sda->srcu_ctrs[0];
> }
> EXPORT_SYMBOL_GPL(__srcu_read_lock_nmisafe);
>
> @@ -1152,6 +1151,8 @@ static void srcu_flip(struct srcu_struct *ssp)
> smp_mb(); /* E */ /* Pairs with B and C. */
>
> WRITE_ONCE(ssp->srcu_idx, ssp->srcu_idx + 1); // Flip the counter.
> + WRITE_ONCE(ssp->srcu_ctrp,
> + &ssp->sda->srcu_ctrs[!(ssp->srcu_ctrp -
> &ssp->sda->srcu_ctrs[0])]);
>
> /*
> * Ensure that if the updater misses an __srcu_read_unlock()
> @@ -1998,6 +1999,7 @@ static int srcu_module_coming(struct module *mod)
> for (i = 0; i < mod->num_srcu_structs; i++) {
> ssp = *(sspp++);
> ssp->sda = alloc_percpu(struct srcu_data);
> + ssp->srcu_ctrp = &ssp->sda->srcu_ctrs[0];
> if (WARN_ON_ONCE(!ssp->sda))
> return -ENOMEM;
- ssp->srcu_ctrp = &ssp->sda->srcu_ctrs[0];
if (WARN_ON_ONCE(!ssp->sda))
return -ENOMEM;
+ ssp->srcu_ctrp = &ssp->sda->srcu_ctrs[0];
Thanks
Zqiang
> }
