[PATCH] srcutree: Add lockdep and early-boot checks to synchronize_srcu_atomic()

[PATCH] srcutree: Add lockdep and early-boot checks to synchronize_srcu_atomic()

[Kunwu Chan]

Add the lockdep annotation, same-type SRCU nesting warning, and
early-boot check used by __synchronize_srcu().

Suggested-by: Zqiang <qiang.zhang@linux.dev>
Signed-off-by: Kunwu Chan <kunwu.chan@gmail.com>
---
 kernel/rcu/srcutree.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/kernel/rcu/srcutree.c b/kernel/rcu/srcutree.c
index 6a9c432a3bd0..6c729e805fb3 100644
--- a/kernel/rcu/srcutree.c
+++ b/kernel/rcu/srcutree.c
@@ -2123,6 +2123,14 @@ void synchronize_srcu_atomic(struct srcu_struct *ssp)
 	unsigned long rdm0, rdm1;
 	unsigned long unlocks0, unlocks1;
 
+	srcu_lock_sync(&ssp->dep_map);
+
+	RCU_LOCKDEP_WARN(lockdep_is_held(ssp),
+			 "Illegal synchronize_srcu_atomic() in same-type SRCU read-side critical section");
+
+	if (rcu_scheduler_active == RCU_SCHEDULER_INACTIVE)
+		return;
+
 	// Initialize.	Either init_srcu_struct() was invoked or
 	// DEFINE_SRCU() or similar was used.  Therefore, no allocation
 	// will be done here.
-- 
2.43.0

Re: [PATCH] srcutree: Add lockdep and early-boot checks to synchronize_srcu_atomic()

[Paul E. McKenney]

On Fri, Sep 11, 2026 at 05:35:15PM +0800, Kunwu Chan wrote:
> Add the lockdep annotation, same-type SRCU nesting warning, and
> early-boot check used by __synchronize_srcu().
> 
> Suggested-by: Zqiang <qiang.zhang@linux.dev>
> Signed-off-by: Kunwu Chan <kunwu.chan@gmail.com>

Queued for review and testing, thank you both!

Interestingly enough, it is now the case that there is a grace-period
wait that can be placed in a normal RCU read-side critical section.
Does this mean that we should also adjust the --do-srcu-lockdep testing
in tools/testing/selftests/rcutorture/bin/torture.sh?

							Thanx, Paul

> ---
>  kernel/rcu/srcutree.c | 8 ++++++++
>  1 file changed, 8 insertions(+)
> 
> diff --git a/kernel/rcu/srcutree.c b/kernel/rcu/srcutree.c
> index 6a9c432a3bd0..6c729e805fb3 100644
> --- a/kernel/rcu/srcutree.c
> +++ b/kernel/rcu/srcutree.c
> @@ -2123,6 +2123,14 @@ void synchronize_srcu_atomic(struct srcu_struct *ssp)
>  	unsigned long rdm0, rdm1;
>  	unsigned long unlocks0, unlocks1;
>  
> +	srcu_lock_sync(&ssp->dep_map);
> +
> +	RCU_LOCKDEP_WARN(lockdep_is_held(ssp),
> +			 "Illegal synchronize_srcu_atomic() in same-type SRCU read-side critical section");
> +
> +	if (rcu_scheduler_active == RCU_SCHEDULER_INACTIVE)
> +		return;
> +
>  	// Initialize.	Either init_srcu_struct() was invoked or
>  	// DEFINE_SRCU() or similar was used.  Therefore, no allocation
>  	// will be done here.
> -- 
> 2.43.0
> 

Re: [PATCH] srcutree: Add lockdep and early-boot checks to synchronize_srcu_atomic()

[KunWu Chan]

On Sat, Sep 12, 2026 at 12:47 AM Paul E. McKenney <paulmck@kernel.org> wrote:
>
> On Fri, Sep 11, 2026 at 05:35:15PM +0800, Kunwu Chan wrote:
> > Add the lockdep annotation, same-type SRCU nesting warning, and
> > early-boot check used by __synchronize_srcu().
> >
> > Suggested-by: Zqiang <qiang.zhang@linux.dev>
> > Signed-off-by: Kunwu Chan <kunwu.chan@gmail.com>
>
> Queued for review and testing, thank you both!
>
> Interestingly enough, it is now the case that there is a grace-period
> wait that can be placed in a normal RCU read-side critical section.
> Does this mean that we should also adjust the --do-srcu-lockdep testing
> in tools/testing/selftests/rcutorture/bin/torture.sh?

Thanks, Paul. Good point.

I’ll check the current `--do-srcu-lockdep` coverage, including the
case where `synchronize_srcu_atomic()` is called from a normal RCU
read-side critical section, and follow up with the necessary torture
testing changes.

Thanks,
Kunwu

>
>                                                         Thanx, Paul
>
> > ---
> >  kernel/rcu/srcutree.c | 8 ++++++++
> >  1 file changed, 8 insertions(+)
> >
> > diff --git a/kernel/rcu/srcutree.c b/kernel/rcu/srcutree.c
> > index 6a9c432a3bd0..6c729e805fb3 100644
> > --- a/kernel/rcu/srcutree.c
> > +++ b/kernel/rcu/srcutree.c
> > @@ -2123,6 +2123,14 @@ void synchronize_srcu_atomic(struct srcu_struct *ssp)
> >       unsigned long rdm0, rdm1;
> >       unsigned long unlocks0, unlocks1;
> >
> > +     srcu_lock_sync(&ssp->dep_map);
> > +
> > +     RCU_LOCKDEP_WARN(lockdep_is_held(ssp),
> > +                      "Illegal synchronize_srcu_atomic() in same-type SRCU read-side critical section");
> > +
> > +     if (rcu_scheduler_active == RCU_SCHEDULER_INACTIVE)
> > +             return;
> > +
> >       // Initialize.  Either init_srcu_struct() was invoked or
> >       // DEFINE_SRCU() or similar was used.  Therefore, no allocation
> >       // will be done here.
> > --
> > 2.43.0
> >

Re: [PATCH] srcutree: Add lockdep and early-boot checks to synchronize_srcu_atomic()

[Paul E. McKenney]

On Sat, Sep 12, 2026 at 08:37:33PM +0800, KunWu Chan wrote:
> On Sat, Sep 12, 2026 at 12:47 AM Paul E. McKenney <paulmck@kernel.org> wrote:
> >
> > On Fri, Sep 11, 2026 at 05:35:15PM +0800, Kunwu Chan wrote:
> > > Add the lockdep annotation, same-type SRCU nesting warning, and
> > > early-boot check used by __synchronize_srcu().
> > >
> > > Suggested-by: Zqiang <qiang.zhang@linux.dev>
> > > Signed-off-by: Kunwu Chan <kunwu.chan@gmail.com>
> >
> > Queued for review and testing, thank you both!
> >
> > Interestingly enough, it is now the case that there is a grace-period
> > wait that can be placed in a normal RCU read-side critical section.
> > Does this mean that we should also adjust the --do-srcu-lockdep testing
> > in tools/testing/selftests/rcutorture/bin/torture.sh?
> 
> Thanks, Paul. Good point.
> 
> I’ll check the current `--do-srcu-lockdep` coverage, including the
> case where `synchronize_srcu_atomic()` is called from a normal RCU
> read-side critical section, and follow up with the necessary torture
> testing changes.

Sounds good!

Perhaps you and Zqiang can work together on this.  Co-developed-by,
for example.

							Thanx, Paul

> Thanks,
> Kunwu
> 
> >
> >                                                         Thanx, Paul
> >
> > > ---
> > >  kernel/rcu/srcutree.c | 8 ++++++++
> > >  1 file changed, 8 insertions(+)
> > >
> > > diff --git a/kernel/rcu/srcutree.c b/kernel/rcu/srcutree.c
> > > index 6a9c432a3bd0..6c729e805fb3 100644
> > > --- a/kernel/rcu/srcutree.c
> > > +++ b/kernel/rcu/srcutree.c
> > > @@ -2123,6 +2123,14 @@ void synchronize_srcu_atomic(struct srcu_struct *ssp)
> > >       unsigned long rdm0, rdm1;
> > >       unsigned long unlocks0, unlocks1;
> > >
> > > +     srcu_lock_sync(&ssp->dep_map);
> > > +
> > > +     RCU_LOCKDEP_WARN(lockdep_is_held(ssp),
> > > +                      "Illegal synchronize_srcu_atomic() in same-type SRCU read-side critical section");
> > > +
> > > +     if (rcu_scheduler_active == RCU_SCHEDULER_INACTIVE)
> > > +             return;
> > > +
> > >       // Initialize.  Either init_srcu_struct() was invoked or
> > >       // DEFINE_SRCU() or similar was used.  Therefore, no allocation
> > >       // will be done here.
> > > --
> > > 2.43.0
> > >

Re: [PATCH] srcutree: Add lockdep and early-boot checks to synchronize_srcu_atomic()

[Zqiang]

> 
> On Sat, Sep 12, 2026 at 08:37:33PM +0800, KunWu Chan wrote:
> 
> > 
> > On Sat, Sep 12, 2026 at 12:47 AM Paul E. McKenney <paulmck@kernel.org> wrote:
> > 
> >  On Fri, Sep 11, 2026 at 05:35:15PM +0800, Kunwu Chan wrote:
> >  > Add the lockdep annotation, same-type SRCU nesting warning, and
> >  > early-boot check used by __synchronize_srcu().
> >  >
> >  > Suggested-by: Zqiang <qiang.zhang@linux.dev>
> >  > Signed-off-by: Kunwu Chan <kunwu.chan@gmail.com>
> > 
> >  Queued for review and testing, thank you both!
> > 
> >  Interestingly enough, it is now the case that there is a grace-period
> >  wait that can be placed in a normal RCU read-side critical section.
> >  Does this mean that we should also adjust the --do-srcu-lockdep testing
> >  in tools/testing/selftests/rcutorture/bin/torture.sh?
> >  
> >  Thanks, Paul. Good point.
> >  
> >  I’ll check the current `--do-srcu-lockdep` coverage, including the
> >  case where `synchronize_srcu_atomic()` is called from a normal RCU
> >  read-side critical section, and follow up with the necessary torture
> >  testing changes.
> > 
> Sounds good!
> 
> Perhaps you and Zqiang can work together on this. Co-developed-by,
> for example.

Hi, Paul and KunWu

Should we also consider the following situations ?


idx = srcu_read_lock_atomic(srcu)

by interrupt run hardirq context:
   synchronize_rcu_atomic(srcu)

srcu_read_unlock_atomic(srcu, idx)


or:



           CPU0:                                                                  CPU1:                                           

idx = srcu_read_lock_atomic(srcu)

smp_call_function_single(CPU1, som_func, NULL, 1)
to send IPI to CPU1, and sync wait complete.
                                                                   hardirq context or ide task context:

                                                                          some_func()
                                                                          ->synchronize_rcu_atomic(srcu)  

srcu_read_unlock_atomic(srcu, idx)


Add WARN_ON(irqs_disabled()) to synchronize_rcu_atomic() ?

Any thoughts?

Thanks
Zqiang


> 
>  Thanx, Paul
> 
> > 
> > Thanks,
> >  Kunwu
> >  
> > 
> >  Thanx, Paul
> > 
> >  > ---
> >  > kernel/rcu/srcutree.c | 8 ++++++++
> >  > 1 file changed, 8 insertions(+)
> >  >
> >  > diff --git a/kernel/rcu/srcutree.c b/kernel/rcu/srcutree.c
> >  > index 6a9c432a3bd0..6c729e805fb3 100644
> >  > --- a/kernel/rcu/srcutree.c
> >  > +++ b/kernel/rcu/srcutree.c
> >  > @@ -2123,6 +2123,14 @@ void synchronize_srcu_atomic(struct srcu_struct *ssp)
> >  > unsigned long rdm0, rdm1;
> >  > unsigned long unlocks0, unlocks1;
> >  >
> >  > + srcu_lock_sync(&ssp->dep_map);
> >  > +
> >  > + RCU_LOCKDEP_WARN(lockdep_is_held(ssp),
> >  > + "Illegal synchronize_srcu_atomic() in same-type SRCU read-side critical section");
> >  > +
> >  > + if (rcu_scheduler_active == RCU_SCHEDULER_INACTIVE)
> >  > + return;
> >  > +
> >  > // Initialize. Either init_srcu_struct() was invoked or
> >  > // DEFINE_SRCU() or similar was used. Therefore, no allocation
> >  > // will be done here.
> >  > --
> >  > 2.43.0
> >  >
> >
>

Re: [PATCH] srcutree: Add lockdep and early-boot checks to synchronize_srcu_atomic()

[KunWu Chan]

On Sun, Sep 13, 2026 at 2:50 AM Paul E. McKenney <paulmck@kernel.org> wrote:
>
> On Sat, Sep 12, 2026 at 08:37:33PM +0800, KunWu Chan wrote:
> > On Sat, Sep 12, 2026 at 12:47 AM Paul E. McKenney <paulmck@kernel.org> wrote:
> > >
> > > On Fri, Sep 11, 2026 at 05:35:15PM +0800, Kunwu Chan wrote:
> > > > Add the lockdep annotation, same-type SRCU nesting warning, and
> > > > early-boot check used by __synchronize_srcu().
> > > >
> > > > Suggested-by: Zqiang <qiang.zhang@linux.dev>
> > > > Signed-off-by: Kunwu Chan <kunwu.chan@gmail.com>
> > >
> > > Queued for review and testing, thank you both!
> > >
> > > Interestingly enough, it is now the case that there is a grace-period
> > > wait that can be placed in a normal RCU read-side critical section.
> > > Does this mean that we should also adjust the --do-srcu-lockdep testing
> > > in tools/testing/selftests/rcutorture/bin/torture.sh?
> >
> > Thanks, Paul. Good point.
> >
> > I’ll check the current `--do-srcu-lockdep` coverage, including the
> > case where `synchronize_srcu_atomic()` is called from a normal RCU
> > read-side critical section, and follow up with the necessary torture
> > testing changes.
>
> Sounds good!
>
> Perhaps you and Zqiang can work together on this.  Co-developed-by,
> for example.

Thanks, Paul. I'am happy to do that.

@Zqiang, your suggestions on the additional lockdep cases got me
started, and these are now incorporated as testtypes 4 and 5.
Paul's observation that synchronize_srcu_atomic() can legitimately
be called from a normal RCU read-side critical section led to an
additional regression test (testtype 6).

In particular, testtype 6 verifies that calling
synchronize_srcu_atomic() from within rcu_read_lock()/rcu_read_unlock()
does not produce a false-positive lockdep warning.

The atomic SRCU same-type nesting cases are covered by testtype 4
and are expected to trigger the RCU_LOCKDEP_WARN() in
synchronize_srcu_atomic().

The changes are in rcutorture.c and srcu_lockdep.sh; torture.sh
does not need to change. The testing changes are basically complete.

@Zqiang, I'm happy to add:
Co-developed-by: Zqiang <qiang.zhang@linux.dev>
Signed-off-by: Zqiang <qiang.zhang@linux.dev>

if you're OK with that.

Thanks,
Kunwu

>
>                                                         Thanx, Paul
>
> > Thanks,
> > Kunwu
> >
> > >
> > >                                                         Thanx, Paul
> > >
> > > > ---
> > > >  kernel/rcu/srcutree.c | 8 ++++++++
> > > >  1 file changed, 8 insertions(+)
> > > >
> > > > diff --git a/kernel/rcu/srcutree.c b/kernel/rcu/srcutree.c
> > > > index 6a9c432a3bd0..6c729e805fb3 100644
> > > > --- a/kernel/rcu/srcutree.c
> > > > +++ b/kernel/rcu/srcutree.c
> > > > @@ -2123,6 +2123,14 @@ void synchronize_srcu_atomic(struct srcu_struct *ssp)
> > > >       unsigned long rdm0, rdm1;
> > > >       unsigned long unlocks0, unlocks1;
> > > >
> > > > +     srcu_lock_sync(&ssp->dep_map);
> > > > +
> > > > +     RCU_LOCKDEP_WARN(lockdep_is_held(ssp),
> > > > +                      "Illegal synchronize_srcu_atomic() in same-type SRCU read-side critical section");
> > > > +
> > > > +     if (rcu_scheduler_active == RCU_SCHEDULER_INACTIVE)
> > > > +             return;
> > > > +
> > > >       // Initialize.  Either init_srcu_struct() was invoked or
> > > >       // DEFINE_SRCU() or similar was used.  Therefore, no allocation
> > > >       // will be done here.
> > > > --
> > > > 2.43.0
> > > >

Re: [PATCH] srcutree: Add lockdep and early-boot checks to synchronize_srcu_atomic()

[KunWu Chan]

On Sun, Sep 13, 2026 at 2:21 PM Zqiang <qiang.zhang@linux.dev> wrote:
>
> >
> > On Sat, Sep 12, 2026 at 08:37:33PM +0800, KunWu Chan wrote:
> >
> > >
> > > On Sat, Sep 12, 2026 at 12:47 AM Paul E. McKenney <paulmck@kernel.org> wrote:
> > >
> > >  On Fri, Sep 11, 2026 at 05:35:15PM +0800, Kunwu Chan wrote:
> > >  > Add the lockdep annotation, same-type SRCU nesting warning, and
> > >  > early-boot check used by __synchronize_srcu().
> > >  >
> > >  > Suggested-by: Zqiang <qiang.zhang@linux.dev>
> > >  > Signed-off-by: Kunwu Chan <kunwu.chan@gmail.com>
> > >
> > >  Queued for review and testing, thank you both!
> > >
> > >  Interestingly enough, it is now the case that there is a grace-period
> > >  wait that can be placed in a normal RCU read-side critical section.
> > >  Does this mean that we should also adjust the --do-srcu-lockdep testing
> > >  in tools/testing/selftests/rcutorture/bin/torture.sh?
> > >
> > >  Thanks, Paul. Good point.
> > >
> > >  I’ll check the current `--do-srcu-lockdep` coverage, including the
> > >  case where `synchronize_srcu_atomic()` is called from a normal RCU
> > >  read-side critical section, and follow up with the necessary torture
> > >  testing changes.
> > >
> > Sounds good!
> >
> > Perhaps you and Zqiang can work together on this. Co-developed-by,
> > for example.
>
> Hi, Paul and KunWu

Hi Zqiang,

Thanks for pointing out these cases.

>
> Should we also consider the following situations ?
>
>
> idx = srcu_read_lock_atomic(srcu)
>
> by interrupt run hardirq context:
>    synchronize_rcu_atomic(srcu)
>
> srcu_read_unlock_atomic(srcu, idx)

For the same-CPU interrupt case, the existing check in
synchronize_srcu_atomic() already catches it:

    synchronize_srcu_atomic(ssp)
      RCU_LOCKDEP_WARN(lockdep_is_held(ssp),
        "Illegal synchronize_srcu_atomic() in same-type SRCU ...");

lockdep_is_held() resolves to __lock_is_held() (lockdep.c:5612),
which checks current->held_locks[]. The interrupt handler runs with
the same current, so it sees the SRCU dep_map acquired by
srcu_read_lock_atomic().

>
>
> or:
>
>
>
>            CPU0:                                                                  CPU1:
>
> idx = srcu_read_lock_atomic(srcu)
>
> smp_call_function_single(CPU1, som_func, NULL, 1)
> to send IPI to CPU1, and sync wait complete.
>                                                                    hardirq context or ide task context:
>
>                                                                           some_func()
>                                                                           ->synchronize_rcu_atomic(srcu)
>
> srcu_read_unlock_atomic(srcu, idx)

The cross-CPU case is different. current->held_locks[] is part of
struct task_struct (sched.h:1302), so the existing
__lock_is_held() check can only see the current task's held locks.
It cannot see the SRCU read-side lock held by the task running on
another CPU. The same limitation applies to the
lock_is_held(&rcu_lock_map) check in synchronize_srcu() at
srcutree.c:1665.

>
>
> Add WARN_ON(irqs_disabled()) to synchronize_rcu_atomic() ?
>
> Any thoughts?

WARN_ON(irqs_disabled()) wouldn't help with the cross-CPU case:
CPU1 could be running in process context with interrupts enabled, so
the WARN would not trigger. It would also add a false positive for
legitimate hardirq calls. synchronize_srcu_atomic() omits
might_sleep() (compare __synchronize_srcu() at srcutree.c:1676)
because it is designed to work in contexts where sleeping is not
allowed, including hardirq context.

Whether a general cross-CPU read-side-hold check is feasible is an
open question. It would need to account for the read-side state across
CPUs without adding too much overhead to the SRCU read-side fast path.

I'm happy to discuss and explore whether there is a reasonable way to
handle this cross-CPU case.

Thanks,
Kunwu

>
> Thanks
> Zqiang
>
>
> >
> >  Thanx, Paul
> >
> > >
> > > Thanks,
> > >  Kunwu
> > >
> > >
> > >  Thanx, Paul
> > >
> > >  > ---
> > >  > kernel/rcu/srcutree.c | 8 ++++++++
> > >  > 1 file changed, 8 insertions(+)
> > >  >
> > >  > diff --git a/kernel/rcu/srcutree.c b/kernel/rcu/srcutree.c
> > >  > index 6a9c432a3bd0..6c729e805fb3 100644
> > >  > --- a/kernel/rcu/srcutree.c
> > >  > +++ b/kernel/rcu/srcutree.c
> > >  > @@ -2123,6 +2123,14 @@ void synchronize_srcu_atomic(struct srcu_struct *ssp)
> > >  > unsigned long rdm0, rdm1;
> > >  > unsigned long unlocks0, unlocks1;
> > >  >
> > >  > + srcu_lock_sync(&ssp->dep_map);
> > >  > +
> > >  > + RCU_LOCKDEP_WARN(lockdep_is_held(ssp),
> > >  > + "Illegal synchronize_srcu_atomic() in same-type SRCU read-side critical section");
> > >  > +
> > >  > + if (rcu_scheduler_active == RCU_SCHEDULER_INACTIVE)
> > >  > + return;
> > >  > +
> > >  > // Initialize. Either init_srcu_struct() was invoked or
> > >  > // DEFINE_SRCU() or similar was used. Therefore, no allocation
> > >  > // will be done here.
> > >  > --
> > >  > 2.43.0
> > >  >
> > >
> >