[PATCH 0/9] rcu: Improve callback diagnostics and validation

[PATCH 0/9] rcu: Improve callback diagnostics and validation

[Kunwu Chan]

Hi,

This series improves callback diagnostics and validation across RCU,
SRCU, and RCU Tasks.

Patches 1-3 record callback registration stacks for KASAN in Tree
SRCU, Tiny SRCU, and Tiny RCU, matching the existing behavior in
Tree RCU.  This preserves the original registration site in KASAN
reports when callbacks are deferred through irq_work.

Patches 4-6 add rcu_head alignment and NULL callback-function
checks to SRCU, Tiny RCU, and RCU Tasks, consistent with the
existing checks in Tree RCU.

Patches 7-9 detect duplicate callback enqueue attempts at
registration time, report the callback address, function symbol,
and object information, and limit diagnostics to the first three
occurrences.  In Tree SRCU, moving the check from srcu_do_enqueue()
to __call_srcu() rejects detected duplicate registrations before
they reach the deferred-list enqueue path.

The duplicate-enqueue checks rely on the existing RCU head
debug-object mechanism and are effective only when
CONFIG_DEBUG_OBJECTS_RCU_HEAD is enabled.  They provide
diagnostics, not full protection against concurrent registration
of the same rcu_head, which violates the API contract.

Tested by rcutorture with KASAN enabled: SRCU-N, SRCU-P, SRCU-T,
SRCU-U, TINY01, TINY02, and TREE03, each for 3 minutes.  All
configurations completed with exitcode 0.

The KASAN aux stack was verified with a custom UAF module: the
"Last potentially related work creation" line in the KASAN report
identified the original __call_srcu() registration site.

A targeted Tree SRCU test module exercised duplicate enqueue
detection on both the direct and irqs-off deferred paths with
CONFIG_DEBUG_OBJECTS_RCU_HEAD=y.  Both paths rejected the
duplicate at __call_srcu() entry without list corruption or
hangs.

A targeted Tiny SRCU test module exercised NULL callback
rejection, duplicate enqueue detection, and post-callback
rcu_head reuse with CONFIG_DEBUG_OBJECTS_RCU_HEAD=y.  The
first two tests produced the expected diagnostics, and the
callback and reuse tests completed without hangs or stale
debug-object state.

RCU Tasks duplicate enqueue detection was verified by code
inspection; no targeted runtime test has been performed for
that path.
 
Kunwu Chan (9):
  srcu: Record callback registration stack for KASAN
  srcutiny: Record callback registration stack for KASAN
  rcu: Record callback registration stack for Tiny RCU
  srcu: Validate callback arguments
  rcu: Validate callback arguments in Tiny RCU
  rcu-tasks: Validate callback arguments
  srcu: Detect duplicate callback enqueue at registration
  srcutiny: Detect duplicate callback enqueue
  rcu-tasks: Detect duplicate callback enqueue

 kernel/rcu/srcutiny.c | 30 ++++++++++++++++++++++++++++++
 kernel/rcu/srcutree.c | 32 ++++++++++++++++++++++++++------
 kernel/rcu/tasks.h    | 22 ++++++++++++++++++++++
 kernel/rcu/tiny.c     | 11 +++++++++++
 4 files changed, 89 insertions(+), 6 deletions(-)


base-commit: 940793b926aa94bf65ec404043050888e3053188
-- 
2.43.0

[PATCH 1/9] srcu: Record callback registration stack for KASAN

[Kunwu Chan]

Record the callback registration stack in __call_srcu()
for KASAN diagnostics involving SRCU callbacks.

Suggested-by: Zqiang <qiang.zhang@linux.dev>
Signed-off-by: Kunwu Chan <chentao@kylinos.cn>
---
 kernel/rcu/srcutree.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/kernel/rcu/srcutree.c b/kernel/rcu/srcutree.c
index 2b0e2b2d2c18..46fe2f0cef85 100644
--- a/kernel/rcu/srcutree.c
+++ b/kernel/rcu/srcutree.c
@@ -20,6 +20,7 @@
 #include <linux/percpu.h>
 #include <linux/preempt.h>
 #include <linux/irq_work.h>
+#include <linux/kasan.h>
 #include <linux/llist.h>
 #include <linux/rcupdate_wait.h>
 #include <linux/sched.h>
@@ -1530,6 +1531,10 @@ static void __call_srcu(struct srcu_struct *ssp, struct rcu_head *rhp,
 {
 	if (WARN_ON_ONCE(ssp->srcu_reader_flavor == SRCU_READ_FLAVOR_ATOMIC))
 		return; // Leak the callback rather than corrupt SRCU state.
+
+	/* Record the caller: the irq_work's stack says nothing about it. */
+	kasan_record_aux_stack(rhp);
+
 	if (should_rcu_defer()) {
 		struct srcu_defer *sndp = this_cpu_ptr(&srcu_defer);
 		struct srcu_data *sdp;
-- 
2.43.0

Re: [PATCH 1/9] srcu: Record callback registration stack for KASAN

[Paul E. McKenney]

On Fri, Oct 23, 2026 at 06:18:33PM +0800, Kunwu Chan wrote:
> Record the callback registration stack in __call_srcu()
> for KASAN diagnostics involving SRCU callbacks.
> 
> Suggested-by: Zqiang <qiang.zhang@linux.dev>
> Signed-off-by: Kunwu Chan <chentao@kylinos.cn>

For 1/9-3/9, looks good if there is a kasan_print_aux_stacks() called
somewhere from 7/9-9/9.  I am not seeing it, but then again, I do not
claim to be a KASAN expert.

							Thanx, Paul

> ---
>  kernel/rcu/srcutree.c | 5 +++++
>  1 file changed, 5 insertions(+)
> 
> diff --git a/kernel/rcu/srcutree.c b/kernel/rcu/srcutree.c
> index 2b0e2b2d2c18..46fe2f0cef85 100644
> --- a/kernel/rcu/srcutree.c
> +++ b/kernel/rcu/srcutree.c
> @@ -20,6 +20,7 @@
>  #include <linux/percpu.h>
>  #include <linux/preempt.h>
>  #include <linux/irq_work.h>
> +#include <linux/kasan.h>
>  #include <linux/llist.h>
>  #include <linux/rcupdate_wait.h>
>  #include <linux/sched.h>
> @@ -1530,6 +1531,10 @@ static void __call_srcu(struct srcu_struct *ssp, struct rcu_head *rhp,
>  {
>  	if (WARN_ON_ONCE(ssp->srcu_reader_flavor == SRCU_READ_FLAVOR_ATOMIC))
>  		return; // Leak the callback rather than corrupt SRCU state.
> +
> +	/* Record the caller: the irq_work's stack says nothing about it. */
> +	kasan_record_aux_stack(rhp);
> +
>  	if (should_rcu_defer()) {
>  		struct srcu_defer *sndp = this_cpu_ptr(&srcu_defer);
>  		struct srcu_data *sdp;
> -- 
> 2.43.0
> 

[PATCH 2/9] srcutiny: Record callback registration stack for KASAN

[Kunwu Chan]

Record the callback registration stack in call_srcu()
for KASAN diagnostics involving Tiny SRCU callbacks.

Suggested-by: Zqiang <qiang.zhang@linux.dev>
Signed-off-by: Kunwu Chan <chentao@kylinos.cn>
---
 kernel/rcu/srcutiny.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/kernel/rcu/srcutiny.c b/kernel/rcu/srcutiny.c
index 63a3f0a8bc53..3ee28885b96f 100644
--- a/kernel/rcu/srcutiny.c
+++ b/kernel/rcu/srcutiny.c
@@ -10,6 +10,7 @@
 
 #include <linux/export.h>
 #include <linux/irq_work.h>
+#include <linux/kasan.h>
 #include <linux/llist.h>
 #include <linux/mutex.h>
 #include <linux/preempt.h>
@@ -290,6 +291,9 @@ EXPORT_SYMBOL_GPL(srcu_defer_drain);
 void call_srcu(struct srcu_struct *ssp, struct rcu_head *rhp,
 	       rcu_callback_t func)
 {
+	/* Record the caller: the irq_work's stack says nothing about it. */
+	kasan_record_aux_stack(rhp);
+
 	if (should_rcu_defer()) {
 		/* A re-entrant call_srcu() during the drain would livelock it. */
 		if (READ_ONCE(srcu_defer_draining) && !in_nmi()) {
-- 
2.43.0

[PATCH 3/9] rcu: Record callback registration stack for Tiny RCU

[Kunwu Chan]

Record the callback registration stack in call_rcu()
for KASAN diagnostics involving Tiny RCU callbacks.

Suggested-by: Zqiang <qiang.zhang@linux.dev>
Signed-off-by: Kunwu Chan <chentao@kylinos.cn>
---
 kernel/rcu/tiny.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/kernel/rcu/tiny.c b/kernel/rcu/tiny.c
index 656b6a682e31..bd22fa43108d 100644
--- a/kernel/rcu/tiny.c
+++ b/kernel/rcu/tiny.c
@@ -12,6 +12,7 @@
 #include <linux/completion.h>
 #include <linux/interrupt.h>
 #include <linux/irq_work.h>
+#include <linux/kasan.h>
 #include <linux/llist.h>
 #include <linux/notifier.h>
 #include <linux/rcupdate_wait.h>
@@ -251,6 +252,9 @@ EXPORT_SYMBOL_GPL(synchronize_rcu);
  */
 void call_rcu(struct rcu_head *head, rcu_callback_t func)
 {
+	/* Record the caller: the irq_work's stack says nothing about it. */
+	kasan_record_aux_stack(head);
+
 	if (should_rcu_defer()) {
 		call_rcu_defer(head, func);
 		return;
-- 
2.43.0

[PATCH 4/9] srcu: Validate callback arguments

[Kunwu Chan]

Check callback-head alignment and reject NULL callback
functions in the SRCU callback registration paths.

Signed-off-by: Kunwu Chan <chentao@kylinos.cn>
---
 kernel/rcu/srcutiny.c | 7 +++++++
 kernel/rcu/srcutree.c | 7 +++++++
 2 files changed, 14 insertions(+)

diff --git a/kernel/rcu/srcutiny.c b/kernel/rcu/srcutiny.c
index 3ee28885b96f..98864977bed2 100644
--- a/kernel/rcu/srcutiny.c
+++ b/kernel/rcu/srcutiny.c
@@ -291,6 +291,13 @@ EXPORT_SYMBOL_GPL(srcu_defer_drain);
 void call_srcu(struct srcu_struct *ssp, struct rcu_head *rhp,
 	       rcu_callback_t func)
 {
+	/* Misaligned rcu_head! */
+	WARN_ON_ONCE((unsigned long)rhp & (sizeof(void *) - 1));
+
+	/* Avoid NULL dereference if callback is NULL. */
+	if (WARN_ON_ONCE(!func))
+		return;
+
 	/* Record the caller: the irq_work's stack says nothing about it. */
 	kasan_record_aux_stack(rhp);
 
diff --git a/kernel/rcu/srcutree.c b/kernel/rcu/srcutree.c
index 46fe2f0cef85..1993ddbdb828 100644
--- a/kernel/rcu/srcutree.c
+++ b/kernel/rcu/srcutree.c
@@ -1529,6 +1529,13 @@ static void srcu_do_enqueue(struct srcu_struct *ssp, struct rcu_head *rhp,
 static void __call_srcu(struct srcu_struct *ssp, struct rcu_head *rhp,
 			rcu_callback_t func, bool do_norm)
 {
+	/* Misaligned rcu_head! */
+	WARN_ON_ONCE((unsigned long)rhp & (sizeof(void *) - 1));
+
+	/* Avoid NULL dereference if callback is NULL. */
+	if (WARN_ON_ONCE(!func))
+		return;
+
 	if (WARN_ON_ONCE(ssp->srcu_reader_flavor == SRCU_READ_FLAVOR_ATOMIC))
 		return; // Leak the callback rather than corrupt SRCU state.
 
-- 
2.43.0

Re: [PATCH 4/9] srcu: Validate callback arguments

[Paul E. McKenney]

On Fri, Oct 23, 2026 at 06:18:36PM +0800, Kunwu Chan wrote:
> Check callback-head alignment and reject NULL callback
> functions in the SRCU callback registration paths.
> 
> Signed-off-by: Kunwu Chan <chentao@kylinos.cn>

For 4/9-6/9:

Reviewed-by: Paul E. McKenney <paulmck@kernel.org>

> ---
>  kernel/rcu/srcutiny.c | 7 +++++++
>  kernel/rcu/srcutree.c | 7 +++++++
>  2 files changed, 14 insertions(+)
> 
> diff --git a/kernel/rcu/srcutiny.c b/kernel/rcu/srcutiny.c
> index 3ee28885b96f..98864977bed2 100644
> --- a/kernel/rcu/srcutiny.c
> +++ b/kernel/rcu/srcutiny.c
> @@ -291,6 +291,13 @@ EXPORT_SYMBOL_GPL(srcu_defer_drain);
>  void call_srcu(struct srcu_struct *ssp, struct rcu_head *rhp,
>  	       rcu_callback_t func)
>  {
> +	/* Misaligned rcu_head! */
> +	WARN_ON_ONCE((unsigned long)rhp & (sizeof(void *) - 1));
> +
> +	/* Avoid NULL dereference if callback is NULL. */
> +	if (WARN_ON_ONCE(!func))
> +		return;
> +
>  	/* Record the caller: the irq_work's stack says nothing about it. */
>  	kasan_record_aux_stack(rhp);
>  
> diff --git a/kernel/rcu/srcutree.c b/kernel/rcu/srcutree.c
> index 46fe2f0cef85..1993ddbdb828 100644
> --- a/kernel/rcu/srcutree.c
> +++ b/kernel/rcu/srcutree.c
> @@ -1529,6 +1529,13 @@ static void srcu_do_enqueue(struct srcu_struct *ssp, struct rcu_head *rhp,
>  static void __call_srcu(struct srcu_struct *ssp, struct rcu_head *rhp,
>  			rcu_callback_t func, bool do_norm)
>  {
> +	/* Misaligned rcu_head! */
> +	WARN_ON_ONCE((unsigned long)rhp & (sizeof(void *) - 1));
> +
> +	/* Avoid NULL dereference if callback is NULL. */
> +	if (WARN_ON_ONCE(!func))
> +		return;
> +
>  	if (WARN_ON_ONCE(ssp->srcu_reader_flavor == SRCU_READ_FLAVOR_ATOMIC))
>  		return; // Leak the callback rather than corrupt SRCU state.
>  
> -- 
> 2.43.0
> 

[PATCH 5/9] rcu: Validate callback arguments in Tiny RCU

[Kunwu Chan]

Check callback-head alignment and reject NULL callback
functions in Tiny RCU's call_rcu() path.

Signed-off-by: Kunwu Chan <chentao@kylinos.cn>
---
 kernel/rcu/tiny.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/kernel/rcu/tiny.c b/kernel/rcu/tiny.c
index bd22fa43108d..ef0b0474f207 100644
--- a/kernel/rcu/tiny.c
+++ b/kernel/rcu/tiny.c
@@ -252,6 +252,13 @@ EXPORT_SYMBOL_GPL(synchronize_rcu);
  */
 void call_rcu(struct rcu_head *head, rcu_callback_t func)
 {
+	/* Misaligned rcu_head! */
+	WARN_ON_ONCE((unsigned long)head & (sizeof(void *) - 1));
+
+	/* Avoid NULL dereference if callback is NULL. */
+	if (WARN_ON_ONCE(!func))
+		return;
+
 	/* Record the caller: the irq_work's stack says nothing about it. */
 	kasan_record_aux_stack(head);
 
-- 
2.43.0

[PATCH 6/9] rcu-tasks: Validate callback arguments

[Kunwu Chan]

Check callback-head alignment and reject NULL callback
functions in the generic RCU Tasks callback registration path.

Signed-off-by: Kunwu Chan <chentao@kylinos.cn>
---
 kernel/rcu/tasks.h | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/kernel/rcu/tasks.h b/kernel/rcu/tasks.h
index fcac7361ec51..5d7f234795b4 100644
--- a/kernel/rcu/tasks.h
+++ b/kernel/rcu/tasks.h
@@ -351,6 +351,13 @@ static void call_rcu_tasks_generic(struct rcu_head *rhp, rcu_callback_t func,
 	bool needwake;
 	struct rcu_tasks_percpu *rtpcp;
 
+	/* Misaligned rcu_head! */
+	WARN_ON_ONCE((unsigned long)rhp & (sizeof(void *) - 1));
+
+	/* Avoid NULL dereference if callback is NULL. */
+	if (WARN_ON_ONCE(!func))
+		return;
+
 	rhp->next = NULL;
 	rhp->func = func;
 	local_irq_save(flags);
-- 
2.43.0

[PATCH 7/9] srcu: Detect duplicate callback enqueue at registration

[Kunwu Chan]

Move the duplicate-callback check from srcu_do_enqueue() to
__call_srcu() entry so that detected duplicate registrations
are rejected before they reach the deferred-list enqueue path.
Report the callback address, function symbol, and object
information, rate-limited to the first three occurrences.

Signed-off-by: Kunwu Chan <chentao@kylinos.cn>
---
 kernel/rcu/srcutree.c | 20 ++++++++++++++------
 1 file changed, 14 insertions(+), 6 deletions(-)

diff --git a/kernel/rcu/srcutree.c b/kernel/rcu/srcutree.c
index 1993ddbdb828..3838d9fdf532 100644
--- a/kernel/rcu/srcutree.c
+++ b/kernel/rcu/srcutree.c
@@ -27,6 +27,7 @@
 #include <linux/smp.h>
 #include <linux/delay.h>
 #include <linux/module.h>
+#include <linux/mm.h>
 #include <linux/slab.h>
 #include <linux/srcu.h>
 
@@ -1511,12 +1512,6 @@ static unsigned long srcu_gp_start_if_needed(struct srcu_struct *ssp,
 static void srcu_do_enqueue(struct srcu_struct *ssp, struct rcu_head *rhp,
 			    rcu_callback_t func, bool do_norm)
 {
-	if (debug_rcu_head_queue(rhp)) {
-		/* Probable double call_srcu(), so leak the callback. */
-		WRITE_ONCE(rhp->func, srcu_leak_callback);
-		WARN_ONCE(1, "call_srcu(): Leaked duplicate callback\n");
-		return;
-	}
 	rhp->func = func;
 	(void)srcu_gp_start_if_needed(ssp, rhp, do_norm);
 }
@@ -1529,6 +1524,8 @@ static void srcu_do_enqueue(struct srcu_struct *ssp, struct rcu_head *rhp,
 static void __call_srcu(struct srcu_struct *ssp, struct rcu_head *rhp,
 			rcu_callback_t func, bool do_norm)
 {
+	static atomic_t doublefrees;
+
 	/* Misaligned rcu_head! */
 	WARN_ON_ONCE((unsigned long)rhp & (sizeof(void *) - 1));
 
@@ -1539,6 +1536,16 @@ static void __call_srcu(struct srcu_struct *ssp, struct rcu_head *rhp,
 	if (WARN_ON_ONCE(ssp->srcu_reader_flavor == SRCU_READ_FLAVOR_ATOMIC))
 		return; // Leak the callback rather than corrupt SRCU state.
 
+	if (debug_rcu_head_queue(rhp)) {
+		if (atomic_inc_return(&doublefrees) < 4) {
+			pr_err("%s(): Duplicate call_srcu() CB %p->%pS()\n",
+			       __func__, rhp, rhp->func);
+			mem_dump_obj(rhp);
+		}
+		WRITE_ONCE(rhp->func, srcu_leak_callback);
+		return;
+	}
+
 	/* Record the caller: the irq_work's stack says nothing about it. */
 	kasan_record_aux_stack(rhp);
 
@@ -1554,6 +1561,7 @@ static void __call_srcu(struct srcu_struct *ssp, struct rcu_head *rhp,
 		if (READ_ONCE(sndp->draining) && !in_nmi()) {
 			WARN_ONCE(IS_ENABLED(CONFIG_PROVE_RCU),
 				  "call_srcu() re-entered during callback drain; leaking callback\n");
+			debug_rcu_head_unqueue(rhp);
 			return;
 		}
 		sdp = this_cpu_ptr(ssp->sda);
-- 
2.43.0

Re: [PATCH 7/9] srcu: Detect duplicate callback enqueue at registration

[Paul E. McKenney]

On Fri, Oct 23, 2026 at 06:18:39PM +0800, Kunwu Chan wrote:
> Move the duplicate-callback check from srcu_do_enqueue() to
> __call_srcu() entry so that detected duplicate registrations
> are rejected before they reach the deferred-list enqueue path.
> Report the callback address, function symbol, and object
> information, rate-limited to the first three occurrences.
> 
> Signed-off-by: Kunwu Chan <chentao@kylinos.cn>

Getting the stackof the call_srcu() once double-enqueue is detected
would be a very good thing!

One question below.

> ---
>  kernel/rcu/srcutree.c | 20 ++++++++++++++------
>  1 file changed, 14 insertions(+), 6 deletions(-)
> 
> diff --git a/kernel/rcu/srcutree.c b/kernel/rcu/srcutree.c
> index 1993ddbdb828..3838d9fdf532 100644
> --- a/kernel/rcu/srcutree.c
> +++ b/kernel/rcu/srcutree.c
> @@ -27,6 +27,7 @@
>  #include <linux/smp.h>
>  #include <linux/delay.h>
>  #include <linux/module.h>
> +#include <linux/mm.h>
>  #include <linux/slab.h>
>  #include <linux/srcu.h>
>  
> @@ -1511,12 +1512,6 @@ static unsigned long srcu_gp_start_if_needed(struct srcu_struct *ssp,
>  static void srcu_do_enqueue(struct srcu_struct *ssp, struct rcu_head *rhp,
>  			    rcu_callback_t func, bool do_norm)
>  {
> -	if (debug_rcu_head_queue(rhp)) {
> -		/* Probable double call_srcu(), so leak the callback. */
> -		WRITE_ONCE(rhp->func, srcu_leak_callback);
> -		WARN_ONCE(1, "call_srcu(): Leaked duplicate callback\n");
> -		return;
> -	}
>  	rhp->func = func;
>  	(void)srcu_gp_start_if_needed(ssp, rhp, do_norm);
>  }
> @@ -1529,6 +1524,8 @@ static void srcu_do_enqueue(struct srcu_struct *ssp, struct rcu_head *rhp,
>  static void __call_srcu(struct srcu_struct *ssp, struct rcu_head *rhp,
>  			rcu_callback_t func, bool do_norm)
>  {
> +	static atomic_t doublefrees;
> +
>  	/* Misaligned rcu_head! */
>  	WARN_ON_ONCE((unsigned long)rhp & (sizeof(void *) - 1));
>  
> @@ -1539,6 +1536,16 @@ static void __call_srcu(struct srcu_struct *ssp, struct rcu_head *rhp,
>  	if (WARN_ON_ONCE(ssp->srcu_reader_flavor == SRCU_READ_FLAVOR_ATOMIC))
>  		return; // Leak the callback rather than corrupt SRCU state.
>  
> +	if (debug_rcu_head_queue(rhp)) {
> +		if (atomic_inc_return(&doublefrees) < 4) {

Why this hard-coded 4?  Why not 3 or 5?  Should this be adjustable via
Kconfig or kernel boot parameter?  Or, alternatively, should the below
pr_err() instead be pr_err_ratelimited()?

> +			pr_err("%s(): Duplicate call_srcu() CB %p->%pS()\n",
> +			       __func__, rhp, rhp->func);
> +			mem_dump_obj(rhp);

Does any of this automatically dump out the stack that was recorded
in earlier patches in this series?

> +		}
> +		WRITE_ONCE(rhp->func, srcu_leak_callback);
> +		return;
> +	}
> +
>  	/* Record the caller: the irq_work's stack says nothing about it. */
>  	kasan_record_aux_stack(rhp);
>  
> @@ -1554,6 +1561,7 @@ static void __call_srcu(struct srcu_struct *ssp, struct rcu_head *rhp,
>  		if (READ_ONCE(sndp->draining) && !in_nmi()) {
>  			WARN_ONCE(IS_ENABLED(CONFIG_PROVE_RCU),
>  				  "call_srcu() re-entered during callback drain; leaking callback\n");
> +			debug_rcu_head_unqueue(rhp);
>  			return;
>  		}
>  		sdp = this_cpu_ptr(ssp->sda);
> -- 
> 2.43.0
> 

Re: [PATCH 7/9] srcu: Detect duplicate callback enqueue at registration

[Paul E. McKenney]

On Fri, Oct 23, 2026 at 12:30:57PM -0700, Paul E. McKenney wrote:
> On Fri, Oct 23, 2026 at 06:18:39PM +0800, Kunwu Chan wrote:
> > Move the duplicate-callback check from srcu_do_enqueue() to
> > __call_srcu() entry so that detected duplicate registrations
> > are rejected before they reach the deferred-list enqueue path.
> > Report the callback address, function symbol, and object
> > information, rate-limited to the first three occurrences.
> > 
> > Signed-off-by: Kunwu Chan <chentao@kylinos.cn>
> 
> Getting the stackof the call_srcu() once double-enqueue is detected
> would be a very good thing!
> 
> One question below.
> 
> > ---
> >  kernel/rcu/srcutree.c | 20 ++++++++++++++------
> >  1 file changed, 14 insertions(+), 6 deletions(-)
> > 
> > diff --git a/kernel/rcu/srcutree.c b/kernel/rcu/srcutree.c
> > index 1993ddbdb828..3838d9fdf532 100644
> > --- a/kernel/rcu/srcutree.c
> > +++ b/kernel/rcu/srcutree.c
> > @@ -27,6 +27,7 @@
> >  #include <linux/smp.h>
> >  #include <linux/delay.h>
> >  #include <linux/module.h>
> > +#include <linux/mm.h>
> >  #include <linux/slab.h>
> >  #include <linux/srcu.h>
> >  
> > @@ -1511,12 +1512,6 @@ static unsigned long srcu_gp_start_if_needed(struct srcu_struct *ssp,
> >  static void srcu_do_enqueue(struct srcu_struct *ssp, struct rcu_head *rhp,
> >  			    rcu_callback_t func, bool do_norm)
> >  {
> > -	if (debug_rcu_head_queue(rhp)) {
> > -		/* Probable double call_srcu(), so leak the callback. */
> > -		WRITE_ONCE(rhp->func, srcu_leak_callback);
> > -		WARN_ONCE(1, "call_srcu(): Leaked duplicate callback\n");
> > -		return;
> > -	}
> >  	rhp->func = func;
> >  	(void)srcu_gp_start_if_needed(ssp, rhp, do_norm);
> >  }
> > @@ -1529,6 +1524,8 @@ static void srcu_do_enqueue(struct srcu_struct *ssp, struct rcu_head *rhp,
> >  static void __call_srcu(struct srcu_struct *ssp, struct rcu_head *rhp,
> >  			rcu_callback_t func, bool do_norm)
> >  {
> > +	static atomic_t doublefrees;
> > +
> >  	/* Misaligned rcu_head! */
> >  	WARN_ON_ONCE((unsigned long)rhp & (sizeof(void *) - 1));
> >  
> > @@ -1539,6 +1536,16 @@ static void __call_srcu(struct srcu_struct *ssp, struct rcu_head *rhp,
> >  	if (WARN_ON_ONCE(ssp->srcu_reader_flavor == SRCU_READ_FLAVOR_ATOMIC))
> >  		return; // Leak the callback rather than corrupt SRCU state.
> >  
> > +	if (debug_rcu_head_queue(rhp)) {
> > +		if (atomic_inc_return(&doublefrees) < 4) {
> 
> Why this hard-coded 4?  Why not 3 or 5?  Should this be adjustable via
> Kconfig or kernel boot parameter?  Or, alternatively, should the below
> pr_err() instead be pr_err_ratelimited()?
> 
> > +			pr_err("%s(): Duplicate call_srcu() CB %p->%pS()\n",
> > +			       __func__, rhp, rhp->func);
> > +			mem_dump_obj(rhp);
> 
> Does any of this automatically dump out the stack that was recorded
> in earlier patches in this series?

As in shouldn't there be a kasan_print_aux_stacks() in there somewhere?
I did not see an call from mem_dump_obj(), but I could easily have
missed it.

							Thanx, Paul

> > +		}
> > +		WRITE_ONCE(rhp->func, srcu_leak_callback);
> > +		return;
> > +	}
> > +
> >  	/* Record the caller: the irq_work's stack says nothing about it. */
> >  	kasan_record_aux_stack(rhp);
> >  
> > @@ -1554,6 +1561,7 @@ static void __call_srcu(struct srcu_struct *ssp, struct rcu_head *rhp,
> >  		if (READ_ONCE(sndp->draining) && !in_nmi()) {
> >  			WARN_ONCE(IS_ENABLED(CONFIG_PROVE_RCU),
> >  				  "call_srcu() re-entered during callback drain; leaking callback\n");
> > +			debug_rcu_head_unqueue(rhp);
> >  			return;
> >  		}
> >  		sdp = this_cpu_ptr(ssp->sda);
> > -- 
> > 2.43.0
> > 

[PATCH 8/9] srcutiny: Detect duplicate callback enqueue

[Kunwu Chan]

Detect duplicate callback enqueue attempts at call_srcu()
entry, before the deferred list can be corrupted.

Signed-off-by: Kunwu Chan <chentao@kylinos.cn>
---
 kernel/rcu/srcutiny.c | 19 +++++++++++++++++++
 1 file changed, 19 insertions(+)

diff --git a/kernel/rcu/srcutiny.c b/kernel/rcu/srcutiny.c
index 98864977bed2..4400fd2b41b7 100644
--- a/kernel/rcu/srcutiny.c
+++ b/kernel/rcu/srcutiny.c
@@ -12,6 +12,7 @@
 #include <linux/irq_work.h>
 #include <linux/kasan.h>
 #include <linux/llist.h>
+#include <linux/mm.h>
 #include <linux/mutex.h>
 #include <linux/preempt.h>
 #include <linux/rcupdate_wait.h>
@@ -178,6 +179,7 @@ void srcu_drive_gp(struct work_struct *wp)
 	while (lh) {
 		rhp = lh;
 		lh = lh->next;
+		debug_rcu_head_unqueue(rhp);
 		debug_rcu_head_callback(rhp);
 		local_bh_disable();
 		rhp->func(rhp);
@@ -235,6 +237,8 @@ static void srcu_gp_start_if_needed(struct srcu_struct *ssp)
  * Also called by __srcu_defer_drain() to re-issue a deferred callback, so it
  * must not re-check the deferral condition.
  */
+static void srcu_leak_callback(struct rcu_head *rhp) { }
+
 static void srcu_do_enqueue(struct srcu_struct *ssp, struct rcu_head *rhp,
 			    rcu_callback_t func)
 {
@@ -272,6 +276,8 @@ static void __srcu_defer_drain(struct srcu_struct *ssp)
 	llist_for_each_safe(node, next, llist_del_all(&ssp->defer_cbs)) {
 		struct rcu_head *rhp = (struct rcu_head *)node;
 
+		/* Bounds a node self-linked by a double call_srcu(). */
+		rhp->next = NULL;
 		srcu_do_enqueue(ssp, rhp, rhp->func);
 	}
 	local_irq_restore(flags);
@@ -291,6 +297,8 @@ EXPORT_SYMBOL_GPL(srcu_defer_drain);
 void call_srcu(struct srcu_struct *ssp, struct rcu_head *rhp,
 	       rcu_callback_t func)
 {
+	static atomic_t doublefrees;
+
 	/* Misaligned rcu_head! */
 	WARN_ON_ONCE((unsigned long)rhp & (sizeof(void *) - 1));
 
@@ -298,6 +306,16 @@ void call_srcu(struct srcu_struct *ssp, struct rcu_head *rhp,
 	if (WARN_ON_ONCE(!func))
 		return;
 
+	if (debug_rcu_head_queue(rhp)) {
+		if (atomic_inc_return(&doublefrees) < 4) {
+			pr_err("%s(): Duplicate call_srcu() CB %p->%pS()\n",
+			       __func__, rhp, rhp->func);
+			mem_dump_obj(rhp);
+		}
+		WRITE_ONCE(rhp->func, srcu_leak_callback);
+		return;
+	}
+
 	/* Record the caller: the irq_work's stack says nothing about it. */
 	kasan_record_aux_stack(rhp);
 
@@ -306,6 +324,7 @@ void call_srcu(struct srcu_struct *ssp, struct rcu_head *rhp,
 		if (READ_ONCE(srcu_defer_draining) && !in_nmi()) {
 			WARN_ONCE(IS_ENABLED(CONFIG_PROVE_RCU),
 				  "call_srcu() re-entered during callback drain; leaking callback\n");
+			debug_rcu_head_unqueue(rhp);
 			return;
 		}
 		rhp->func = func;
-- 
2.43.0

Re: [PATCH 8/9] srcutiny: Detect duplicate callback enqueue

[Paul E. McKenney]

On Fri, Oct 23, 2026 at 06:18:40PM +0800, Kunwu Chan wrote:
> Detect duplicate callback enqueue attempts at call_srcu()
> entry, before the deferred list can be corrupted.
> 
> Signed-off-by: Kunwu Chan <chentao@kylinos.cn>

Same questions as for the previous patch.  ;-)

							Thanx, Paul

> ---
>  kernel/rcu/srcutiny.c | 19 +++++++++++++++++++
>  1 file changed, 19 insertions(+)
> 
> diff --git a/kernel/rcu/srcutiny.c b/kernel/rcu/srcutiny.c
> index 98864977bed2..4400fd2b41b7 100644
> --- a/kernel/rcu/srcutiny.c
> +++ b/kernel/rcu/srcutiny.c
> @@ -12,6 +12,7 @@
>  #include <linux/irq_work.h>
>  #include <linux/kasan.h>
>  #include <linux/llist.h>
> +#include <linux/mm.h>
>  #include <linux/mutex.h>
>  #include <linux/preempt.h>
>  #include <linux/rcupdate_wait.h>
> @@ -178,6 +179,7 @@ void srcu_drive_gp(struct work_struct *wp)
>  	while (lh) {
>  		rhp = lh;
>  		lh = lh->next;
> +		debug_rcu_head_unqueue(rhp);
>  		debug_rcu_head_callback(rhp);
>  		local_bh_disable();
>  		rhp->func(rhp);
> @@ -235,6 +237,8 @@ static void srcu_gp_start_if_needed(struct srcu_struct *ssp)
>   * Also called by __srcu_defer_drain() to re-issue a deferred callback, so it
>   * must not re-check the deferral condition.
>   */
> +static void srcu_leak_callback(struct rcu_head *rhp) { }
> +
>  static void srcu_do_enqueue(struct srcu_struct *ssp, struct rcu_head *rhp,
>  			    rcu_callback_t func)
>  {
> @@ -272,6 +276,8 @@ static void __srcu_defer_drain(struct srcu_struct *ssp)
>  	llist_for_each_safe(node, next, llist_del_all(&ssp->defer_cbs)) {
>  		struct rcu_head *rhp = (struct rcu_head *)node;
>  
> +		/* Bounds a node self-linked by a double call_srcu(). */
> +		rhp->next = NULL;
>  		srcu_do_enqueue(ssp, rhp, rhp->func);
>  	}
>  	local_irq_restore(flags);
> @@ -291,6 +297,8 @@ EXPORT_SYMBOL_GPL(srcu_defer_drain);
>  void call_srcu(struct srcu_struct *ssp, struct rcu_head *rhp,
>  	       rcu_callback_t func)
>  {
> +	static atomic_t doublefrees;
> +
>  	/* Misaligned rcu_head! */
>  	WARN_ON_ONCE((unsigned long)rhp & (sizeof(void *) - 1));
>  
> @@ -298,6 +306,16 @@ void call_srcu(struct srcu_struct *ssp, struct rcu_head *rhp,
>  	if (WARN_ON_ONCE(!func))
>  		return;
>  
> +	if (debug_rcu_head_queue(rhp)) {
> +		if (atomic_inc_return(&doublefrees) < 4) {
> +			pr_err("%s(): Duplicate call_srcu() CB %p->%pS()\n",
> +			       __func__, rhp, rhp->func);
> +			mem_dump_obj(rhp);
> +		}
> +		WRITE_ONCE(rhp->func, srcu_leak_callback);
> +		return;
> +	}
> +
>  	/* Record the caller: the irq_work's stack says nothing about it. */
>  	kasan_record_aux_stack(rhp);
>  
> @@ -306,6 +324,7 @@ void call_srcu(struct srcu_struct *ssp, struct rcu_head *rhp,
>  		if (READ_ONCE(srcu_defer_draining) && !in_nmi()) {
>  			WARN_ONCE(IS_ENABLED(CONFIG_PROVE_RCU),
>  				  "call_srcu() re-entered during callback drain; leaking callback\n");
> +			debug_rcu_head_unqueue(rhp);
>  			return;
>  		}
>  		rhp->func = func;
> -- 
> 2.43.0
> 

[PATCH 9/9] rcu-tasks: Detect duplicate callback enqueue

[Kunwu Chan]

Detect duplicate callback enqueue attempts in the generic
RCU Tasks callback registration path.

Signed-off-by: Kunwu Chan <chentao@kylinos.cn>
---
 kernel/rcu/tasks.h | 15 +++++++++++++++
 1 file changed, 15 insertions(+)

diff --git a/kernel/rcu/tasks.h b/kernel/rcu/tasks.h
index 5d7f234795b4..49b716feb31d 100644
--- a/kernel/rcu/tasks.h
+++ b/kernel/rcu/tasks.h
@@ -6,6 +6,7 @@
  */
 
 #ifdef CONFIG_TASKS_RCU_GENERIC
+#include <linux/mm.h>
 #include "rcu_segcblist.h"
 
 ////////////////////////////////////////////////////////////////////////
@@ -339,9 +340,12 @@ static void call_rcu_tasks_iw_wakeup(struct irq_work *iwp)
 }
 
 // Enqueue a callback for the specified flavor of Tasks RCU.
+static void rcu_tasks_leak_callback(struct rcu_head *rhp) { }
+
 static void call_rcu_tasks_generic(struct rcu_head *rhp, rcu_callback_t func,
 				   struct rcu_tasks *rtp)
 {
+	static atomic_t doublefrees;
 	int chosen_cpu;
 	unsigned long flags;
 	bool havekthread = smp_load_acquire(&rtp->kthread_ptr);
@@ -358,6 +362,16 @@ static void call_rcu_tasks_generic(struct rcu_head *rhp, rcu_callback_t func,
 	if (WARN_ON_ONCE(!func))
 		return;
 
+	if (debug_rcu_head_queue(rhp)) {
+		if (atomic_inc_return(&doublefrees) < 4) {
+			pr_err("%s(): Duplicate call_rcu_%s() CB %p->%pS()\n",
+			       __func__, rtp->name, rhp, rhp->func);
+			mem_dump_obj(rhp);
+		}
+		WRITE_ONCE(rhp->func, rcu_tasks_leak_callback);
+		return;
+	}
+
 	rhp->next = NULL;
 	rhp->func = func;
 	local_irq_save(flags);
@@ -586,6 +600,7 @@ static void rcu_tasks_invoke_cbs(struct rcu_tasks *rtp, struct rcu_tasks_percpu
 	raw_spin_unlock_irqrestore_rcu_node(rtpcp, flags);
 	len = rcl.len;
 	for (rhp = rcu_cblist_dequeue(&rcl); rhp; rhp = rcu_cblist_dequeue(&rcl)) {
+		debug_rcu_head_unqueue(rhp);
 		debug_rcu_head_callback(rhp);
 		local_bh_disable();
 		rhp->func(rhp);
-- 
2.43.0

Re: [PATCH 9/9] rcu-tasks: Detect duplicate callback enqueue

[Paul E. McKenney]

On Fri, Oct 23, 2026 at 06:18:41PM +0800, Kunwu Chan wrote:
> Detect duplicate callback enqueue attempts in the generic
> RCU Tasks callback registration path.
> 
> Signed-off-by: Kunwu Chan <chentao@kylinos.cn>

And the same questions for this patch as well.  ;-)

							Thanx, Paul

> ---
>  kernel/rcu/tasks.h | 15 +++++++++++++++
>  1 file changed, 15 insertions(+)
> 
> diff --git a/kernel/rcu/tasks.h b/kernel/rcu/tasks.h
> index 5d7f234795b4..49b716feb31d 100644
> --- a/kernel/rcu/tasks.h
> +++ b/kernel/rcu/tasks.h
> @@ -6,6 +6,7 @@
>   */
>  
>  #ifdef CONFIG_TASKS_RCU_GENERIC
> +#include <linux/mm.h>
>  #include "rcu_segcblist.h"
>  
>  ////////////////////////////////////////////////////////////////////////
> @@ -339,9 +340,12 @@ static void call_rcu_tasks_iw_wakeup(struct irq_work *iwp)
>  }
>  
>  // Enqueue a callback for the specified flavor of Tasks RCU.
> +static void rcu_tasks_leak_callback(struct rcu_head *rhp) { }
> +
>  static void call_rcu_tasks_generic(struct rcu_head *rhp, rcu_callback_t func,
>  				   struct rcu_tasks *rtp)
>  {
> +	static atomic_t doublefrees;
>  	int chosen_cpu;
>  	unsigned long flags;
>  	bool havekthread = smp_load_acquire(&rtp->kthread_ptr);
> @@ -358,6 +362,16 @@ static void call_rcu_tasks_generic(struct rcu_head *rhp, rcu_callback_t func,
>  	if (WARN_ON_ONCE(!func))
>  		return;
>  
> +	if (debug_rcu_head_queue(rhp)) {
> +		if (atomic_inc_return(&doublefrees) < 4) {
> +			pr_err("%s(): Duplicate call_rcu_%s() CB %p->%pS()\n",
> +			       __func__, rtp->name, rhp, rhp->func);
> +			mem_dump_obj(rhp);
> +		}
> +		WRITE_ONCE(rhp->func, rcu_tasks_leak_callback);
> +		return;
> +	}
> +
>  	rhp->next = NULL;
>  	rhp->func = func;
>  	local_irq_save(flags);
> @@ -586,6 +600,7 @@ static void rcu_tasks_invoke_cbs(struct rcu_tasks *rtp, struct rcu_tasks_percpu
>  	raw_spin_unlock_irqrestore_rcu_node(rtpcp, flags);
>  	len = rcl.len;
>  	for (rhp = rcu_cblist_dequeue(&rcl); rhp; rhp = rcu_cblist_dequeue(&rcl)) {
> +		debug_rcu_head_unqueue(rhp);
>  		debug_rcu_head_callback(rhp);
>  		local_bh_disable();
>  		rhp->func(rhp);
> -- 
> 2.43.0
>