sched: WARNING: at include/linux/cpumask.h:108 select_fallback_rq+0x241/0x280()

sched: WARNING: at include/linux/cpumask.h:108 select_fallback_rq+0x241/0x280()

[Sasha Levin]

(and now with lkml)

Hi all,

I got the following spew using trinity in a kvm tools guest on the
latest linux-next kernel.

This is the result of trying to offline CPU1. I'm not sure how to
reproduce it easily besides putting some pressure on the system and
shutting down CPUs until it happens.

[  317.238839] Cannot set affinity for irq 0
[  317.238839] ------------[ cut here ]------------
[  317.238839] WARNING: at include/linux/cpumask.h:108
select_fallback_rq+0x241/0x280()
[  317.238839] Pid: 13, comm: migration/1 Not tainted
3.3.0-next-20120329-sasha #4
[  317.238839] Call Trace:
[  317.238839]  [<ffffffff810b26b5>] warn_slowpath_common+0x75/0xb0
[  317.238839]  [<ffffffff810b2705>] warn_slowpath_null+0x15/0x20
[  317.238839]  [<ffffffff810e5991>] select_fallback_rq+0x241/0x280
[  317.238839]  [<ffffffff810f1a40>] ? dequeue_task_fair+0x100/0x100
[  317.238839]  [<ffffffff810f1a40>] ? dequeue_task_fair+0x100/0x100
[  317.238839]  [<ffffffff810ecd20>] migrate_tasks+0x80/0xf0
[  317.238839]  [<ffffffff826fe03a>] ? migration_call+0xae/0x16b
[  317.238839]  [<ffffffff826fe073>] migration_call+0xe7/0x16b
[  317.238839]  [<ffffffff810ddebf>] notifier_call_chain+0x5f/0x150
[  317.238839]  [<ffffffff810ddfb9>] __raw_notifier_call_chain+0x9/0x10
[  317.238839]  [<ffffffff810b489b>] __cpu_notify+0x1b/0x30
[  317.238839]  [<ffffffff826c3fbd>] take_cpu_down+0x2d/0x40
[  317.238839]  [<ffffffff811357fa>] stop_machine_cpu_stop+0xda/0x1a0
[  317.238839]  [<ffffffff81135720>] ? queue_stop_cpus_work+0x190/0x190
[  317.238839]  [<ffffffff811352ae>] cpu_stopper_thread+0xee/0x200
[  317.238839]  [<ffffffff82705c1a>] ? __schedule+0x49a/0x860
[  317.238839]  [<ffffffff811351c0>] ? res_counter_init+0x50/0x50
[  317.238839]  [<ffffffff810d715e>] kthread+0xbe/0xd0
[  317.238839]  [<ffffffff82709e74>] kernel_thread_helper+0x4/0x10
[  317.238839]  [<ffffffff810e3ee0>] ? finish_task_switch+0x80/0x110
[  317.238839]  [<ffffffff82708174>] ? retint_restore_args+0x13/0x13
[  317.238839]  [<ffffffff810d70a0>] ? __init_kthread_worker+0x70/0x70
[  317.238839]  [<ffffffff82709e70>] ? gs_change+0x13/0x13
[  317.238839] ---[ end trace 79079cf527253aab ]---
[  317.250645] [sched_delayed] process 2267 (trinity) no longer affine to cpu1
[  317.323711] CPU 1 is now offline
[  317.591059] [sched_delayed] process 1956 (trinity) no longer affine to cpu1
[  317.812110] [sched_delayed] process 2004 (trinity) no longer affine to cpu1
[  318.401016] [sched_delayed] process 2228 (trinity) no longer affine to cpu1
[  318.581015] [sched_delayed] process 2099 (trinity) no longer affine to cpu1

Re: sched: WARNING: at include/linux/cpumask.h:108 select_fallback_rq+0x241/0x280()

[Srivatsa S. Bhat]

On 03/30/2012 02:02 AM, Sasha Levin wrote:

> (and now with lkml)
> 
> Hi all,
> 
> I got the following spew using trinity in a kvm tools guest on the
> latest linux-next kernel.
> 
> This is the result of trying to offline CPU1. I'm not sure how to
> reproduce it easily besides putting some pressure on the system and
> shutting down CPUs until it happens.
> 
> [  317.238839] Cannot set affinity for irq 0
> [  317.238839] ------------[ cut here ]------------
> [  317.238839] WARNING: at include/linux/cpumask.h:108
> select_fallback_rq+0x241/0x280()
> [  317.238839] Pid: 13, comm: migration/1 Not tainted
> 3.3.0-next-20120329-sasha #4
> [  317.238839] Call Trace:
> [  317.238839]  [<ffffffff810b26b5>] warn_slowpath_common+0x75/0xb0
> [  317.238839]  [<ffffffff810b2705>] warn_slowpath_null+0x15/0x20
> [  317.238839]  [<ffffffff810e5991>] select_fallback_rq+0x241/0x280
> [  317.238839]  [<ffffffff810f1a40>] ? dequeue_task_fair+0x100/0x100
> [  317.238839]  [<ffffffff810f1a40>] ? dequeue_task_fair+0x100/0x100
> [  317.238839]  [<ffffffff810ecd20>] migrate_tasks+0x80/0xf0
> [  317.238839]  [<ffffffff826fe03a>] ? migration_call+0xae/0x16b
> [  317.238839]  [<ffffffff826fe073>] migration_call+0xe7/0x16b
> [  317.238839]  [<ffffffff810ddebf>] notifier_call_chain+0x5f/0x150
> [  317.238839]  [<ffffffff810ddfb9>] __raw_notifier_call_chain+0x9/0x10
> [  317.238839]  [<ffffffff810b489b>] __cpu_notify+0x1b/0x30
> [  317.238839]  [<ffffffff826c3fbd>] take_cpu_down+0x2d/0x40
> [  317.238839]  [<ffffffff811357fa>] stop_machine_cpu_stop+0xda/0x1a0
> [  317.238839]  [<ffffffff81135720>] ? queue_stop_cpus_work+0x190/0x190
> [  317.238839]  [<ffffffff811352ae>] cpu_stopper_thread+0xee/0x200
> [  317.238839]  [<ffffffff82705c1a>] ? __schedule+0x49a/0x860
> [  317.238839]  [<ffffffff811351c0>] ? res_counter_init+0x50/0x50
> [  317.238839]  [<ffffffff810d715e>] kthread+0xbe/0xd0
> [  317.238839]  [<ffffffff82709e74>] kernel_thread_helper+0x4/0x10
> [  317.238839]  [<ffffffff810e3ee0>] ? finish_task_switch+0x80/0x110
> [  317.238839]  [<ffffffff82708174>] ? retint_restore_args+0x13/0x13
> [  317.238839]  [<ffffffff810d70a0>] ? __init_kthread_worker+0x70/0x70
> [  317.238839]  [<ffffffff82709e70>] ? gs_change+0x13/0x13
> [  317.238839] ---[ end trace 79079cf527253aab ]---
> [  317.250645] [sched_delayed] process 2267 (trinity) no longer affine to cpu1
> [  317.323711] CPU 1 is now offline
> [  317.591059] [sched_delayed] process 1956 (trinity) no longer affine to cpu1
> [  317.812110] [sched_delayed] process 2004 (trinity) no longer affine to cpu1
> [  318.401016] [sched_delayed] process 2228 (trinity) no longer affine to cpu1
> [  318.581015] [sched_delayed] process 2099 (trinity) no longer affine to cpu1
> --



Does this patch help?

---

From: Srivatsa S. Bhat <srivatsa.bhat@linux.vnet.ibm.com>
Subject: sched: Fix incorrect usage of for_each_cpu_mask() in select_fallback_rq()

The function for_each_cpu_mask() expects a *pointer* to struct cpumask
as its second argument, whereas select_fallback_rq() passes the value
itself. And moreover, for_each_cpu_mask() has been marked as obselete
in include/linux/cpumask.h. So move to the more appropriate for_each_cpu()
variant.

Reported-by: Sasha Levin <levinsasha928@gmail.com>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Signed-off-by: Srivatsa S. Bhat <srivatsa.bhat@linux.vnet.ibm.com>
---

 kernel/sched/core.c |    4 ++--
 1 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index e3ed0ec..e85046d 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -1270,7 +1270,7 @@ static int select_fallback_rq(int cpu, struct task_struct *p)
 	int dest_cpu;
 
 	/* Look for allowed, online CPU in same node. */
-	for_each_cpu_mask(dest_cpu, *nodemask) {
+	for_each_cpu(dest_cpu, nodemask) {
 		if (!cpu_online(dest_cpu))
 			continue;
 		if (!cpu_active(dest_cpu))
@@ -1281,7 +1281,7 @@ static int select_fallback_rq(int cpu, struct task_struct *p)
 
 	for (;;) {
 		/* Any allowed, online CPU? */
-		for_each_cpu_mask(dest_cpu, *tsk_cpus_allowed(p)) {
+		for_each_cpu(dest_cpu, tsk_cpus_allowed(p)) {
 			if (!cpu_online(dest_cpu))
 				continue;
 			if (!cpu_active(dest_cpu))

Re: sched: WARNING: at include/linux/cpumask.h:108 select_fallback_rq+0x241/0x280()

[Peter Zijlstra]

On Fri, 2012-03-30 at 19:40 +0530, Srivatsa S. Bhat wrote:

> From: Srivatsa S. Bhat <srivatsa.bhat@linux.vnet.ibm.com>
> Subject: sched: Fix incorrect usage of for_each_cpu_mask() in select_fallback_rq()
> 
> The function for_each_cpu_mask() expects a *pointer* to struct cpumask
> as its second argument, whereas select_fallback_rq() passes the value
> itself. And moreover, for_each_cpu_mask() has been marked as obselete
> in include/linux/cpumask.h. So move to the more appropriate for_each_cpu()
> variant.

Gah.. so why did it compile to begin with!?

> Reported-by: Sasha Levin <levinsasha928@gmail.com>
> Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
> Signed-off-by: Srivatsa S. Bhat <srivatsa.bhat@linux.vnet.ibm.com>
> ---
> 
>  kernel/sched/core.c |    4 ++--
>  1 files changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> index e3ed0ec..e85046d 100644
> --- a/kernel/sched/core.c
> +++ b/kernel/sched/core.c
> @@ -1270,7 +1270,7 @@ static int select_fallback_rq(int cpu, struct task_struct *p)
>  	int dest_cpu;
>  
>  	/* Look for allowed, online CPU in same node. */
> -	for_each_cpu_mask(dest_cpu, *nodemask) {
> +	for_each_cpu(dest_cpu, nodemask) {
>  		if (!cpu_online(dest_cpu))
>  			continue;
>  		if (!cpu_active(dest_cpu))
> @@ -1281,7 +1281,7 @@ static int select_fallback_rq(int cpu, struct task_struct *p)
>  
>  	for (;;) {
>  		/* Any allowed, online CPU? */
> -		for_each_cpu_mask(dest_cpu, *tsk_cpus_allowed(p)) {
> +		for_each_cpu(dest_cpu, tsk_cpus_allowed(p)) {
>  			if (!cpu_online(dest_cpu))
>  				continue;
>  			if (!cpu_active(dest_cpu))
> 
> 

Re: sched: WARNING: at include/linux/cpumask.h:108 select_fallback_rq+0x241/0x280()

[Sasha Levin]

On Fri, Mar 30, 2012 at 5:10 PM, Srivatsa S. Bhat
<srivatsa.bhat@linux.vnet.ibm.com> wrote:
> On 03/30/2012 02:02 AM, Sasha Levin wrote:
>
>> (and now with lkml)
>>
>> Hi all,
>>
>> I got the following spew using trinity in a kvm tools guest on the
>> latest linux-next kernel.
>>
>> This is the result of trying to offline CPU1. I'm not sure how to
>> reproduce it easily besides putting some pressure on the system and
>> shutting down CPUs until it happens.
>>
>> [  317.238839] Cannot set affinity for irq 0
>> [  317.238839] ------------[ cut here ]------------
>> [  317.238839] WARNING: at include/linux/cpumask.h:108
>> select_fallback_rq+0x241/0x280()
>> [  317.238839] Pid: 13, comm: migration/1 Not tainted
>> 3.3.0-next-20120329-sasha #4
>> [  317.238839] Call Trace:
>> [  317.238839]  [<ffffffff810b26b5>] warn_slowpath_common+0x75/0xb0
>> [  317.238839]  [<ffffffff810b2705>] warn_slowpath_null+0x15/0x20
>> [  317.238839]  [<ffffffff810e5991>] select_fallback_rq+0x241/0x280
>> [  317.238839]  [<ffffffff810f1a40>] ? dequeue_task_fair+0x100/0x100
>> [  317.238839]  [<ffffffff810f1a40>] ? dequeue_task_fair+0x100/0x100
>> [  317.238839]  [<ffffffff810ecd20>] migrate_tasks+0x80/0xf0
>> [  317.238839]  [<ffffffff826fe03a>] ? migration_call+0xae/0x16b
>> [  317.238839]  [<ffffffff826fe073>] migration_call+0xe7/0x16b
>> [  317.238839]  [<ffffffff810ddebf>] notifier_call_chain+0x5f/0x150
>> [  317.238839]  [<ffffffff810ddfb9>] __raw_notifier_call_chain+0x9/0x10
>> [  317.238839]  [<ffffffff810b489b>] __cpu_notify+0x1b/0x30
>> [  317.238839]  [<ffffffff826c3fbd>] take_cpu_down+0x2d/0x40
>> [  317.238839]  [<ffffffff811357fa>] stop_machine_cpu_stop+0xda/0x1a0
>> [  317.238839]  [<ffffffff81135720>] ? queue_stop_cpus_work+0x190/0x190
>> [  317.238839]  [<ffffffff811352ae>] cpu_stopper_thread+0xee/0x200
>> [  317.238839]  [<ffffffff82705c1a>] ? __schedule+0x49a/0x860
>> [  317.238839]  [<ffffffff811351c0>] ? res_counter_init+0x50/0x50
>> [  317.238839]  [<ffffffff810d715e>] kthread+0xbe/0xd0
>> [  317.238839]  [<ffffffff82709e74>] kernel_thread_helper+0x4/0x10
>> [  317.238839]  [<ffffffff810e3ee0>] ? finish_task_switch+0x80/0x110
>> [  317.238839]  [<ffffffff82708174>] ? retint_restore_args+0x13/0x13
>> [  317.238839]  [<ffffffff810d70a0>] ? __init_kthread_worker+0x70/0x70
>> [  317.238839]  [<ffffffff82709e70>] ? gs_change+0x13/0x13
>> [  317.238839] ---[ end trace 79079cf527253aab ]---
>> [  317.250645] [sched_delayed] process 2267 (trinity) no longer affine to cpu1
>> [  317.323711] CPU 1 is now offline
>> [  317.591059] [sched_delayed] process 1956 (trinity) no longer affine to cpu1
>> [  317.812110] [sched_delayed] process 2004 (trinity) no longer affine to cpu1
>> [  318.401016] [sched_delayed] process 2228 (trinity) no longer affine to cpu1
>> [  318.581015] [sched_delayed] process 2099 (trinity) no longer affine to cpu1
>> --
>
>
>
> Does this patch help?
>
> ---
>
> From: Srivatsa S. Bhat <srivatsa.bhat@linux.vnet.ibm.com>
> Subject: sched: Fix incorrect usage of for_each_cpu_mask() in select_fallback_rq()
>
> The function for_each_cpu_mask() expects a *pointer* to struct cpumask
> as its second argument, whereas select_fallback_rq() passes the value
> itself. And moreover, for_each_cpu_mask() has been marked as obselete
> in include/linux/cpumask.h. So move to the more appropriate for_each_cpu()
> variant.
>
> Reported-by: Sasha Levin <levinsasha928@gmail.com>
> Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
> Signed-off-by: Srivatsa S. Bhat <srivatsa.bhat@linux.vnet.ibm.com>
> ---

Works for me.

Tested-by: Sasha Levin <levinsasha928@gmail.com>

Re: sched: WARNING: at include/linux/cpumask.h:108 select_fallback_rq+0x241/0x280()

[Srivatsa S. Bhat]

On 03/30/2012 08:15 PM, Peter Zijlstra wrote:

> On Fri, 2012-03-30 at 19:40 +0530, Srivatsa S. Bhat wrote:
> 
>> From: Srivatsa S. Bhat <srivatsa.bhat@linux.vnet.ibm.com>
>> Subject: sched: Fix incorrect usage of for_each_cpu_mask() in select_fallback_rq()
>>
>> The function for_each_cpu_mask() expects a *pointer* to struct cpumask
>> as its second argument, whereas select_fallback_rq() passes the value
>> itself. And moreover, for_each_cpu_mask() has been marked as obselete
>> in include/linux/cpumask.h. So move to the more appropriate for_each_cpu()
>> variant.
> 
> Gah.. so why did it compile to begin with!?


One of the perils of using macros instead of true function calls :-(


Regards,
Srivatsa S. Bhat

> 
>> Reported-by: Sasha Levin <levinsasha928@gmail.com>
>> Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
>> Signed-off-by: Srivatsa S. Bhat <srivatsa.bhat@linux.vnet.ibm.com>
>> ---
>>
>>  kernel/sched/core.c |    4 ++--
>>  1 files changed, 2 insertions(+), 2 deletions(-)
>>
>> diff --git a/kernel/sched/core.c b/kernel/sched/core.c
>> index e3ed0ec..e85046d 100644
>> --- a/kernel/sched/core.c
>> +++ b/kernel/sched/core.c
>> @@ -1270,7 +1270,7 @@ static int select_fallback_rq(int cpu, struct task_struct *p)
>>  	int dest_cpu;
>>  
>>  	/* Look for allowed, online CPU in same node. */
>> -	for_each_cpu_mask(dest_cpu, *nodemask) {
>> +	for_each_cpu(dest_cpu, nodemask) {
>>  		if (!cpu_online(dest_cpu))
>>  			continue;
>>  		if (!cpu_active(dest_cpu))
>> @@ -1281,7 +1281,7 @@ static int select_fallback_rq(int cpu, struct task_struct *p)
>>  
>>  	for (;;) {
>>  		/* Any allowed, online CPU? */
>> -		for_each_cpu_mask(dest_cpu, *tsk_cpus_allowed(p)) {
>> +		for_each_cpu(dest_cpu, tsk_cpus_allowed(p)) {
>>  			if (!cpu_online(dest_cpu))
>>  				continue;
>>  			if (!cpu_active(dest_cpu))
>>
>>
> 
> 
> 

[tip:sched/urgent] sched: Fix incorrect usage of for_each_cpu_mask () in select_fallback_rq()

[tip-bot for Srivatsa S. Bhat]

Commit-ID:  e3831edd59edf57ca11fc289f08961b20baf5146
Gitweb:     http://git.kernel.org/tip/e3831edd59edf57ca11fc289f08961b20baf5146
Author:     Srivatsa S. Bhat <srivatsa.bhat@linux.vnet.ibm.com>
AuthorDate: Fri, 30 Mar 2012 19:40:28 +0530
Committer:  Ingo Molnar <mingo@kernel.org>
CommitDate: Sat, 31 Mar 2012 10:43:36 +0200

sched: Fix incorrect usage of for_each_cpu_mask() in select_fallback_rq()

The function for_each_cpu_mask() expects a *pointer* to struct
cpumask as its second argument, whereas select_fallback_rq()
passes the value itself.

And moreover, for_each_cpu_mask() has been marked as obselete
in include/linux/cpumask.h. So move to the more appropriate
for_each_cpu() variant.

Reported-by: Sasha Levin <levinsasha928@gmail.com>
Signed-off-by: Srivatsa S. Bhat <srivatsa.bhat@linux.vnet.ibm.com>
Acked-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Dave Jones <davej@redhat.com>
Cc: Liu Chuansheng <chuansheng.liu@intel.com>
Cc: vapier@gentoo.org
Cc: rusty@rustcorp.com.au
Link: http://lkml.kernel.org/r/4F75BED4.9050005@linux.vnet.ibm.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
---
 kernel/sched/core.c |    4 ++--
 1 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 985f6e5..8773176 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -1268,7 +1268,7 @@ static int select_fallback_rq(int cpu, struct task_struct *p)
 	int dest_cpu;
 
 	/* Look for allowed, online CPU in same node. */
-	for_each_cpu_mask(dest_cpu, *nodemask) {
+	for_each_cpu(dest_cpu, nodemask) {
 		if (!cpu_online(dest_cpu))
 			continue;
 		if (!cpu_active(dest_cpu))
@@ -1279,7 +1279,7 @@ static int select_fallback_rq(int cpu, struct task_struct *p)
 
 	for (;;) {
 		/* Any allowed, online CPU? */
-		for_each_cpu_mask(dest_cpu, *tsk_cpus_allowed(p)) {
+		for_each_cpu(dest_cpu, tsk_cpus_allowed(p)) {
 			if (!cpu_online(dest_cpu))
 				continue;
 			if (!cpu_active(dest_cpu))

Re: sched: WARNING: at include/linux/cpumask.h:108 select_fallback_rq+0x241/0x280()

[Peter Zijlstra]

On Sat, 2012-03-31 at 13:22 +0530, Srivatsa S. Bhat wrote:
> 
> One of the perils of using macros instead of true function calls :-(
> 
You can do type checking in macros too, its not pretty, but there's
several such things already, see min()/max() for example.

Re: sched: WARNING: at include/linux/cpumask.h:108 select_fallback_rq+0x241/0x280()

[Sasha Levin]

On Sat, Apr 14, 2012 at 11:17 AM, Peter Zijlstra <peterz@infradead.org> wrote:
> On Sat, 2012-03-31 at 13:22 +0530, Srivatsa S. Bhat wrote:
>>
>> One of the perils of using macros instead of true function calls :-(
>>
> You can do type checking in macros too, its not pretty, but there's
> several such things already, see min()/max() for example.

Would it make sense to somehow standardize type checking in kernel
macros? Possibly a set of wrappers that would make type checking easy
to get into new and existing macros?

Re: sched: WARNING: at include/linux/cpumask.h:108 select_fallback_rq+0x241/0x280()

[Peter Zijlstra]

On Sat, 2012-04-14 at 13:40 +0200, Sasha Levin wrote:
> On Sat, Apr 14, 2012 at 11:17 AM, Peter Zijlstra <peterz@infradead.org> wrote:
> > On Sat, 2012-03-31 at 13:22 +0530, Srivatsa S. Bhat wrote:
> >>
> >> One of the perils of using macros instead of true function calls :-(
> >>
> > You can do type checking in macros too, its not pretty, but there's
> > several such things already, see min()/max() for example.
> 
> Would it make sense to somehow standardize type checking in kernel
> macros? Possibly a set of wrappers that would make type checking easy
> to get into new and existing macros?


I had a quick go with the below and that doesn't quite work for no
obvious reasons as of yet.. Also, that call out to cpumask_next() should
already do type validation for us, so still no clue why my earlier code
compiled at all.

---
 include/linux/cpumask.h |    1 +
 include/linux/kernel.h  |   10 ++++++++++
 2 files changed, 11 insertions(+), 0 deletions(-)

diff --git a/include/linux/cpumask.h b/include/linux/cpumask.h
index a2c819d..aec8355 100644
--- a/include/linux/cpumask.h
+++ b/include/linux/cpumask.h
@@ -201,6 +201,7 @@ int cpumask_any_but(const struct cpumask *mask, unsigned int cpu);
  * After the loop, cpu is >= nr_cpu_ids.
  */
 #define for_each_cpu(cpu, mask)				\
+	match_type(const struct cpumask *, (mask));	\
 	for ((cpu) = -1;				\
 		(cpu) = cpumask_next((cpu), (mask)),	\
 		(cpu) < nr_cpu_ids;)
diff --git a/include/linux/kernel.h b/include/linux/kernel.h
index 645231c..bcb7da3 100644
--- a/include/linux/kernel.h
+++ b/include/linux/kernel.h
@@ -549,6 +549,16 @@ ftrace_vprintk(const char *fmt, va_list ap)
 static inline void ftrace_dump(enum ftrace_dump_mode oops_dump_mode) { }
 #endif /* CONFIG_TRACING */
 
+#define match_type_type(t1, t2)			\
+do {						\
+	t1 uninitialized_var(____t1);		\
+	t2 uninitialized_var(____t2);		\
+	(void) (&____t1 == &____t2);		\
+} while (0)
+
+#define match_type(t, v)			\
+	match_type_type(t, typeof(v))
+
 /*
  * min()/max()/clamp() macros that also do
  * strict type-checking.. See the

Re: sched: WARNING: at include/linux/cpumask.h:108 select_fallback_rq+0x241/0x280()

[Sasha Levin]

On Sat, Apr 14, 2012 at 8:12 PM, Peter Zijlstra <peterz@infradead.org> wrote:
> On Sat, 2012-04-14 at 13:40 +0200, Sasha Levin wrote:
>> On Sat, Apr 14, 2012 at 11:17 AM, Peter Zijlstra <peterz@infradead.org> wrote:
>> > On Sat, 2012-03-31 at 13:22 +0530, Srivatsa S. Bhat wrote:
>> >>
>> >> One of the perils of using macros instead of true function calls :-(
>> >>
>> > You can do type checking in macros too, its not pretty, but there's
>> > several such things already, see min()/max() for example.
>>
>> Would it make sense to somehow standardize type checking in kernel
>> macros? Possibly a set of wrappers that would make type checking easy
>> to get into new and existing macros?
>
>
> I had a quick go with the below and that doesn't quite work for no
> obvious reasons as of yet.. Also, that call out to cpumask_next() should
> already do type validation for us, so still no clue why my earlier code
> compiled at all.

I've also started working on it, I have something that looks pretty
good and detects the bug which has caused this discussion.

I want to apply it on several more macros around the kernel and I'll
send a RFC. Basically I want to deal with the cpumask thing, update
min()/max()/etc to use it and convert the list or rbtree macros to use
it as well. It'll give us a good look on how something like that would
look around the kernel.