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;
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);
- 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;
}
