linux-kernel - Re: [PATCH 1/4] add task handling notifier: base definitions

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Date:	Wed, 09 Jan 2008 09:46:25 +0000
From:	"Jan Beulich" <jbeulich@...ell.com>
To:	"Matthew Helsley" <matthltc@...ibm.com>
Cc:	"Paul Jackson" <pj@....com>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/4] add task handling notifier: base definitions

>> +BLOCKING_NOTIFIER_HEAD(task_notifier_list);
>> +EXPORT_SYMBOL_GPL(task_notifier_list);
>> +ATOMIC_NOTIFIER_HEAD(atomic_task_notifier_list);
>> +EXPORT_SYMBOL_GPL(atomic_task_notifier_list);
>> +
>
>When these global notifier lists were proposed years ago folks at SGI
>loudly objected with concerns over anticipated cache line bouncing on
>512+ cpu machines. Is that no longer a concern?

I can't see an alternative, since the serialization is unavoidable.

>> @@ -121,6 +127,9 @@ void __put_task_struct(struct task_struc
>>  	WARN_ON(atomic_read(&tsk->usage));
>>  	WARN_ON(tsk == current);
>> 
>> +	atomic_notifier_call_chain(&atomic_task_notifier_list,
>> +				   TASK_DELETE, tsk);
>> +
>>  	security_task_free(tsk);
>>  	free_uid(tsk->user);
>>  	put_group_info(tsk->group_info);
>
>Would the atomic notifier call chain be necessary if you hooked into an
>earlier section of do_exit() instead?

I'm afraid it is, as I was told that sleeping in the do_exit() path is not
generally possible.

Jan

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