Re: [PATCH v10 07/12] task_isolation: add debug boot flag

[Chris Metcalf <cmetcalf@mellanox.com>]

On 3/2/2016 3:37 PM, Peter Zijlstra wrote:
> On Wed, Mar 02, 2016 at 03:09:31PM -0500, Chris Metcalf wrote:
>> +void task_isolation_debug(int cpu)
>> +{
>> +	struct task_struct *p;
>> +
>> +	if (!task_isolation_possible(cpu))
>> +		return;
>> +
>> +	rcu_read_lock();
>> +	p = cpu_curr(cpu);
>> +	get_task_struct(p);
> As I think Oleg keeps reminding me, this is not actually a safe thing to
> do.

So what's the right solution?  The fast path in task_isolation_debug_task basically
just uses the new "task_isolation_flags", and "pid" and "comm".  I would think those
would all have to be safe because of the get_task_struct().

The piece that might be problematic is the eventual call to send_sig_info() using the
task_struct pointer (called via task_isolation_debug_task -> task_isolation_interrupt).
Clearly this is safe at some level, since that's more or less what sys_kill() does and the
process could similarly evaporate half way through sending the signal.

Suggestions?  Thanks!

-- 
Chris Metcalf, Mellanox Technologies
http://www.mellanox.com