[PATCH] tracing/workqueue: Get rid of searching last executed worklet in probe_worklet_complete()

[PATCH] tracing/workqueue: Get rid of searching last executed worklet in probe_worklet_complete()

[Zhaolei]

We don't need search workqueue's worklet list for worklet which was latest
executed, instead, we can use a pointer in cpu_workqueue_stats to remember
which worklet was just executed.

Thanks Oleg for pointing it out.

Signed-off-by: Zhao Lei <zhaolei@cn.fujitsu.com>
Reported-by: Oleg Nesterov <oleg@redhat.com>
---
 kernel/trace/trace_workqueue.c |   37 +++++++++++++------------------------
 1 files changed, 13 insertions(+), 24 deletions(-)

diff --git a/kernel/trace/trace_workqueue.c b/kernel/trace/trace_workqueue.c
index c67be60..d90f9ac 100644
--- a/kernel/trace/trace_workqueue.c
+++ b/kernel/trace/trace_workqueue.c
@@ -25,13 +25,6 @@ struct workfunc_stats {
 	unsigned int			inserted;
 	unsigned int			executed;
 
-	/*
-	 * save latest work_struct's pointer to use as identifier in
-	 * probe_worklet_complete, because we can't use work_struct->...
-	 * after worklet got executed
-	 */
-	void				*work;
-
 	/* save execution time temporarily for calculate executed time */
 	u64				start_time;
 	u64				max_executed_time;
@@ -46,10 +39,17 @@ struct cpu_workqueue_stats {
 	/* Protected by cpu workqueue lock */
 	unsigned int		inserted;
 	unsigned int		executed;
+
 	/* list of struct workfunc_stats in this workqueue */
 	struct list_head	workfunclist;
 
 	/*
+	 * pointer to last executed worklet's workfunc_stats in this workqueue,
+	 * used by probe_worklet_complete()
+	 */
+	struct workfunc_stats *last_workfunc;
+
+	/*
 	 * the task maybe destroyed when we read stat file
 	 * we define it to void * because we only use it as a identifier
 	 */
@@ -163,7 +163,7 @@ found_wq:
 		if (wfnode->func == work->func) {
 			wfnode->executed++;
 			wfnode->start_time = trace_clock_global();
-			wfnode->work = work;
+			node->last_workfunc = wfnode;
 			goto found_wf;
 		}
 	pr_debug("trace_workqueue: worklet not found\n");
@@ -180,7 +180,7 @@ probe_worklet_complete(struct task_struct *wq_thread, void *work)
 {
 	int cpu = cpumask_first(&wq_thread->cpus_allowed);
 	struct cpu_workqueue_stats *node;
-	struct workfunc_stats *wfnode;
+	u64 executed_time;
 	unsigned long flags;
 
 	spin_lock_irqsave(&workqueue_cpu_stat(cpu)->lock, flags);
@@ -192,22 +192,11 @@ probe_worklet_complete(struct task_struct *wq_thread, void *work)
 	goto end;
 
 found_wq:
-	list_for_each_entry(wfnode, &node->workfunclist, list) {
-		u64 executed_time;
+	executed_time = trace_clock_global() - node->last_workfunc->start_time;
+	node->last_workfunc->total_time += executed_time;
+	if (executed_time > node->last_workfunc->max_executed_time)
+		node->last_workfunc->max_executed_time = executed_time;
 
-		if (wfnode->work != work)
-			continue;
-
-		executed_time = trace_clock_global() - wfnode->start_time;
-		wfnode->total_time += executed_time;
-		if (executed_time > wfnode->max_executed_time)
-			wfnode->max_executed_time = executed_time;
-		goto found_wf;
-	}
-	pr_debug("trace_workqueue: worklet not found\n");
-	goto end;
-
-found_wf:
 end:
 	spin_unlock_irqrestore(&workqueue_cpu_stat(cpu)->lock, flags);
 }
-- 
1.5.5.3

Re: [PATCH] tracing/workqueue: Get rid of searching last executed worklet in probe_worklet_complete()

[Oleg Nesterov]

On 05/21, Zhaolei wrote:
>
> We don't need search workqueue's worklet list for worklet which was latest
> executed, instead, we can use a pointer in cpu_workqueue_stats to remember
> which worklet was just executed.

Minor nit,

> @@ -192,22 +192,11 @@ probe_worklet_complete(struct task_struct *wq_thread, void *work)
>  	goto end;
>
>  found_wq:
> -	list_for_each_entry(wfnode, &node->workfunclist, list) {
> -		u64 executed_time;
> +	executed_time = trace_clock_global() - node->last_workfunc->start_time;
> +	node->last_workfunc->total_time += executed_time;

Suppose that "enqueue" handler fails to allocate the memory for the new
work_struct.

This means that the "execute" handler does not record ->last_workfunc.

In that case probe_worklet_complete() uses the wrong workfunc_stats or
we can even crash if ->last_workfunc == NULL.

I think _execute() should set ->last_workfunc = NULL first, then serach
for wfnode. _complete() should check ->last_workfunc != NULL and return
if it is NULL.

Oleg.

Re: [PATCH] tracing/workqueue: Get rid of searching last executedworklet in probe_worklet_complete()

[Zhaolei]

* From: "Oleg Nesterov" <oleg@redhat.com>
> On 05/21, Zhaolei wrote:
>>
>> We don't need search workqueue's worklet list for worklet which was latest
>> executed, instead, we can use a pointer in cpu_workqueue_stats to remember
>> which worklet was just executed.
> 
> Minor nit,
> 
>> @@ -192,22 +192,11 @@ probe_worklet_complete(struct task_struct *wq_thread, void *work)
>>  goto end;
>>
>>  found_wq:
>> - list_for_each_entry(wfnode, &node->workfunclist, list) {
>> - u64 executed_time;
>> + executed_time = trace_clock_global() - node->last_workfunc->start_time;
>> + node->last_workfunc->total_time += executed_time;
> 
> Suppose that "enqueue" handler fails to allocate the memory for the new
> work_struct.
> 
> This means that the "execute" handler does not record ->last_workfunc.
> 
> In that case probe_worklet_complete() uses the wrong workfunc_stats or
> we can even crash if ->last_workfunc == NULL.
> 
> I think _execute() should set ->last_workfunc = NULL first, then serach
> for wfnode. _complete() should check ->last_workfunc != NULL and return
> if it is NULL.
Hello, Oleg

Thanks!
You are right, I will send v2 to fix this.

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[PATCH v2] tracing/workqueue: Get rid of searching last executed worklet in probe_worklet_complete()

[Zhaolei]

We don't need search workqueue's worklet list for worklet which was latest
executed, instead, we can use a pointer in cpu_workqueue_stats to remember
which worklet was just executed.

Thanks Oleg for pointing it out.

Changelog:
v1->v2: Oleg pointed out that if searching executed workfunc_stats failed
in probe_worklet_execute(), for example, workfunc_stats's memory allocation
failed previously, cpu_workqueue_stats->last_workfunc is not set to correct
value, and it will cause wrong accessing in probe_worklet_complete().
This problem is fixed in v2.

Signed-off-by: Zhao Lei <zhaolei@cn.fujitsu.com>
Reported-by: Oleg Nesterov <oleg@redhat.com>
---
 kernel/trace/trace_workqueue.c |   39 ++++++++++++++++-----------------------
 1 files changed, 16 insertions(+), 23 deletions(-)

diff --git a/kernel/trace/trace_workqueue.c b/kernel/trace/trace_workqueue.c
index c67be60..740de3b 100644
--- a/kernel/trace/trace_workqueue.c
+++ b/kernel/trace/trace_workqueue.c
@@ -25,13 +25,6 @@ struct workfunc_stats {
 	unsigned int			inserted;
 	unsigned int			executed;
 
-	/*
-	 * save latest work_struct's pointer to use as identifier in
-	 * probe_worklet_complete, because we can't use work_struct->...
-	 * after worklet got executed
-	 */
-	void				*work;
-
 	/* save execution time temporarily for calculate executed time */
 	u64				start_time;
 	u64				max_executed_time;
@@ -46,10 +39,17 @@ struct cpu_workqueue_stats {
 	/* Protected by cpu workqueue lock */
 	unsigned int		inserted;
 	unsigned int		executed;
+
 	/* list of struct workfunc_stats in this workqueue */
 	struct list_head	workfunclist;
 
 	/*
+	 * pointer to last executed worklet's workfunc_stats in this workqueue,
+	 * used by probe_worklet_complete()
+	 */
+	struct workfunc_stats *last_workfunc;
+
+	/*
 	 * the task maybe destroyed when we read stat file
 	 * we define it to void * because we only use it as a identifier
 	 */
@@ -163,9 +163,10 @@ found_wq:
 		if (wfnode->func == work->func) {
 			wfnode->executed++;
 			wfnode->start_time = trace_clock_global();
-			wfnode->work = work;
+			node->last_workfunc = wfnode;
 			goto found_wf;
 		}
+	node->last_workfunc = NULL;
 	pr_debug("trace_workqueue: worklet not found\n");
 	goto end;
 
@@ -180,7 +181,7 @@ probe_worklet_complete(struct task_struct *wq_thread, void *work)
 {
 	int cpu = cpumask_first(&wq_thread->cpus_allowed);
 	struct cpu_workqueue_stats *node;
-	struct workfunc_stats *wfnode;
+	u64 executed_time;
 	unsigned long flags;
 
 	spin_lock_irqsave(&workqueue_cpu_stat(cpu)->lock, flags);
@@ -192,22 +193,14 @@ probe_worklet_complete(struct task_struct *wq_thread, void *work)
 	goto end;
 
 found_wq:
-	list_for_each_entry(wfnode, &node->workfunclist, list) {
-		u64 executed_time;
+	if (!node->last_workfunc)
+		goto end;
 
-		if (wfnode->work != work)
-			continue;
+	executed_time = trace_clock_global() - node->last_workfunc->start_time;
+	node->last_workfunc->total_time += executed_time;
+	if (executed_time > node->last_workfunc->max_executed_time)
+		node->last_workfunc->max_executed_time = executed_time;
 
-		executed_time = trace_clock_global() - wfnode->start_time;
-		wfnode->total_time += executed_time;
-		if (executed_time > wfnode->max_executed_time)
-			wfnode->max_executed_time = executed_time;
-		goto found_wf;
-	}
-	pr_debug("trace_workqueue: worklet not found\n");
-	goto end;
-
-found_wf:
 end:
 	spin_unlock_irqrestore(&workqueue_cpu_stat(cpu)->lock, flags);
 }
-- 
1.5.5.3

Re: [PATCH v2] tracing/workqueue: Get rid of searching last executed worklet in probe_worklet_complete()

[Oleg Nesterov]

On 05/22, Zhaolei wrote:
>
> We don't need search workqueue's worklet list for worklet which was latest
> executed, instead, we can use a pointer in cpu_workqueue_stats to remember
> which worklet was just executed.

Thanks Zhao, I think this is correct.

Oleg.

Re: [PATCH v2] tracing/workqueue: Get rid of searching last executed worklet in probe_worklet_complete()

[Frederic Weisbecker]

On Fri, May 22, 2009 at 08:37:39PM +0200, Oleg Nesterov wrote:
> On 05/22, Zhaolei wrote:
> >
> > We don't need search workqueue's worklet list for worklet which was latest
> > executed, instead, we can use a pointer in cpu_workqueue_stats to remember
> > which worklet was just executed.
> 
> Thanks Zhao, I think this is correct.
> 
> Oleg.


May I add your Acked-by then?

Thanks. 

Re: [PATCH v2] tracing/workqueue: Get rid of searching last executed worklet in probe_worklet_complete()

[Oleg Nesterov]

On 05/26, Frederic Weisbecker wrote:
>
> On Fri, May 22, 2009 at 08:37:39PM +0200, Oleg Nesterov wrote:
> > On 05/22, Zhaolei wrote:
> > >
> > > We don't need search workqueue's worklet list for worklet which was latest
> > > executed, instead, we can use a pointer in cpu_workqueue_stats to remember
> > > which worklet was just executed.
> >
> > Thanks Zhao, I think this is correct.
> >
> > Oleg.
>
> May I add your Acked-by then?

Yes, please feel free. Or reviewed-by, whatever you think more right.

Oleg.

Re: [PATCH v2] tracing/workqueue: Get rid of searching last executed worklet in probe_worklet_complete()

[Frederic Weisbecker]

On Fri, May 22, 2009 at 10:40:54AM +0800, Zhaolei wrote:
> We don't need search workqueue's worklet list for worklet which was latest
> executed, instead, we can use a pointer in cpu_workqueue_stats to remember
> which worklet was just executed.
> 
> Thanks Oleg for pointing it out.
> 
> Changelog:
> v1->v2: Oleg pointed out that if searching executed workfunc_stats failed
> in probe_worklet_execute(), for example, workfunc_stats's memory allocation
> failed previously, cpu_workqueue_stats->last_workfunc is not set to correct
> value, and it will cause wrong accessing in probe_worklet_complete().
> This problem is fixed in v2.
> 
> Signed-off-by: Zhao Lei <zhaolei@cn.fujitsu.com>
> Reported-by: Oleg Nesterov <oleg@redhat.com>

Looks good, thanks!

Acked-by: Frederic Weisbecker <fweisbec@gmail.com>

Frederic.


> ---
>  kernel/trace/trace_workqueue.c |   39 ++++++++++++++++-----------------------
>  1 files changed, 16 insertions(+), 23 deletions(-)
> 
> diff --git a/kernel/trace/trace_workqueue.c b/kernel/trace/trace_workqueue.c
> index c67be60..740de3b 100644
> --- a/kernel/trace/trace_workqueue.c
> +++ b/kernel/trace/trace_workqueue.c
> @@ -25,13 +25,6 @@ struct workfunc_stats {
>  	unsigned int			inserted;
>  	unsigned int			executed;
>  
> -	/*
> -	 * save latest work_struct's pointer to use as identifier in
> -	 * probe_worklet_complete, because we can't use work_struct->...
> -	 * after worklet got executed
> -	 */
> -	void				*work;
> -
>  	/* save execution time temporarily for calculate executed time */
>  	u64				start_time;
>  	u64				max_executed_time;
> @@ -46,10 +39,17 @@ struct cpu_workqueue_stats {
>  	/* Protected by cpu workqueue lock */
>  	unsigned int		inserted;
>  	unsigned int		executed;
> +
>  	/* list of struct workfunc_stats in this workqueue */
>  	struct list_head	workfunclist;
>  
>  	/*
> +	 * pointer to last executed worklet's workfunc_stats in this workqueue,
> +	 * used by probe_worklet_complete()
> +	 */
> +	struct workfunc_stats *last_workfunc;
> +
> +	/*
>  	 * the task maybe destroyed when we read stat file
>  	 * we define it to void * because we only use it as a identifier
>  	 */
> @@ -163,9 +163,10 @@ found_wq:
>  		if (wfnode->func == work->func) {
>  			wfnode->executed++;
>  			wfnode->start_time = trace_clock_global();
> -			wfnode->work = work;
> +			node->last_workfunc = wfnode;
>  			goto found_wf;
>  		}
> +	node->last_workfunc = NULL;
>  	pr_debug("trace_workqueue: worklet not found\n");
>  	goto end;
>  
> @@ -180,7 +181,7 @@ probe_worklet_complete(struct task_struct *wq_thread, void *work)
>  {
>  	int cpu = cpumask_first(&wq_thread->cpus_allowed);
>  	struct cpu_workqueue_stats *node;
> -	struct workfunc_stats *wfnode;
> +	u64 executed_time;
>  	unsigned long flags;
>  
>  	spin_lock_irqsave(&workqueue_cpu_stat(cpu)->lock, flags);
> @@ -192,22 +193,14 @@ probe_worklet_complete(struct task_struct *wq_thread, void *work)
>  	goto end;
>  
>  found_wq:
> -	list_for_each_entry(wfnode, &node->workfunclist, list) {
> -		u64 executed_time;
> +	if (!node->last_workfunc)
> +		goto end;
>  
> -		if (wfnode->work != work)
> -			continue;
> +	executed_time = trace_clock_global() - node->last_workfunc->start_time;
> +	node->last_workfunc->total_time += executed_time;
> +	if (executed_time > node->last_workfunc->max_executed_time)
> +		node->last_workfunc->max_executed_time = executed_time;
>  
> -		executed_time = trace_clock_global() - wfnode->start_time;
> -		wfnode->total_time += executed_time;
> -		if (executed_time > wfnode->max_executed_time)
> -			wfnode->max_executed_time = executed_time;
> -		goto found_wf;
> -	}
> -	pr_debug("trace_workqueue: worklet not found\n");
> -	goto end;
> -
> -found_wf:
>  end:
>  	spin_unlock_irqrestore(&workqueue_cpu_stat(cpu)->lock, flags);
>  }
> -- 
> 1.5.5.3
> 
>