[PATCH][OPROFILE] disable preempt when calling smp_processor_id()

[PATCH][OPROFILE] disable preempt when calling smp_processor_id()

[Chris Wright]

Oprofile is hitting many of the below BUG messages.

BUG: using smp_processor_id() in preemptible [00000001] code: sleep/4892
caller is task_exit_notify+0x9/0x17
Call Trace: <ffffffff802ac70f>{smp_processor_id+191}
	    <ffffffff803ff219>{task_exit_notify+9}
	    <ffffffff8014a930>{notifier_call_chain+32}
	    <ffffffff8013d181>{profile_task_exit+49}
	    <ffffffff8013eb22>{do_exit+34}
	    <ffffffff80146490>{process_timeout+0}
	    <ffffffff8013f8c8>{do_group_exit+264}
	    <ffffffff801106b6>{system_call+126}

smp_processor_id() is called w/out preempt disabled.  Use
get_cpu()/put_cpu() instead.  Should this be put_cpu_no_resched()?

Signed-off-by: Chris Wright <chrisw@osdl.org>

--- linux-2.6.10-rc1-mm3-smp_processor_id/drivers/oprofile/buffer_sync.c~orig	2004-11-05 15:21:21.551984200 -0800
+++ linux-2.6.10-rc1-mm3-smp_processor_id/drivers/oprofile/buffer_sync.c	2004-11-05 15:23:29.000000000 -0800
@@ -62,7 +62,8 @@
 	/* To avoid latency problems, we only process the current CPU,
 	 * hoping that most samples for the task are on this CPU
 	 */
-	sync_buffer(smp_processor_id());
+	sync_buffer(get_cpu());
+	put_cpu();
   	return 0;
 }
 
@@ -86,7 +87,8 @@
 		/* To avoid latency problems, we only process the current CPU,
 		 * hoping that most samples for the task are on this CPU
 		 */
-		sync_buffer(smp_processor_id());
+		sync_buffer(get_cpu());
+		put_cpu();
 		return 0;
 	}
 

Re: [PATCH][OPROFILE] disable preempt when calling smp_processor_id()

[John Levon]

On Fri, Nov 05, 2004 at 04:32:21PM -0800, Chris Wright wrote:

> smp_processor_id() is called w/out preempt disabled.  Use
> get_cpu()/put_cpu() instead.  Should this be put_cpu_no_resched()?

No, the patch below looks fine

regards
john

> Signed-off-by: Chris Wright <chrisw@osdl.org>
> 
> --- linux-2.6.10-rc1-mm3-smp_processor_id/drivers/oprofile/buffer_sync.c~orig	2004-11-05 15:21:21.551984200 -0800
> +++ linux-2.6.10-rc1-mm3-smp_processor_id/drivers/oprofile/buffer_sync.c	2004-11-05 15:23:29.000000000 -0800
> @@ -62,7 +62,8 @@
>  	/* To avoid latency problems, we only process the current CPU,
>  	 * hoping that most samples for the task are on this CPU
>  	 */
> -	sync_buffer(smp_processor_id());
> +	sync_buffer(get_cpu());
> +	put_cpu();
>    	return 0;
>  }
>  
> @@ -86,7 +87,8 @@
>  		/* To avoid latency problems, we only process the current CPU,
>  		 * hoping that most samples for the task are on this CPU
>  		 */
> -		sync_buffer(smp_processor_id());
> +		sync_buffer(get_cpu());
> +		put_cpu();
>  		return 0;
>  	}
>  

Re: [PATCH][OPROFILE] disable preempt when calling smp_processor_id()

[Chris Wright]

* John Levon (levon@movementarian.org) wrote:
> On Fri, Nov 05, 2004 at 04:32:21PM -0800, Chris Wright wrote:
> > smp_processor_id() is called w/out preempt disabled.  Use
> > get_cpu()/put_cpu() instead.  Should this be put_cpu_no_resched()?
> 
> No, the patch below looks fine

I realized over the weekend that it's still broken.  And Cliff hit it
in some tests he ran here.  The sync_buffer() function can sleep, and
while the unprotected call to smp_processor_id() is no longer a problem,
scheduling with preempt disabled is.

thanks,
-chris
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