linux-kernel - Re: [RFC][PATCH 3/7] sched,livepatch: Use task_try

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Date:   Thu, 23 Sep 2021 15:17:17 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Petr Mladek <pmladek@...e.com>
Cc:     gor@...ux.ibm.com, jpoimboe@...hat.com, jikos@...nel.org,
        mbenes@...e.cz, mingo@...nel.org, linux-kernel@...r.kernel.org,
        joe.lawrence@...hat.com, fweisbec@...il.com, tglx@...utronix.de,
        hca@...ux.ibm.com, svens@...ux.ibm.com, sumanthk@...ux.ibm.com,
        live-patching@...r.kernel.org, paulmck@...nel.org
Subject: Re: [RFC][PATCH 3/7] sched,livepatch: Use task_try_func()

On Thu, Sep 23, 2021 at 02:05:00PM +0200, Petr Mladek wrote:
> On Wed 2021-09-22 13:05:09, Peter Zijlstra wrote:

> > +static int klp_check_task(struct task_struct *task, void *arg)
> 
> Please, call this klp_check_and_switch_task() to make it clear
> that it actually does the switch.

Sure.


> > +	ret = task_try_func(task, klp_check_task, &old_name);
> > +	switch (ret) {
> > +	case -EBUSY:
> > +		pr_debug("%s: %s:%d is running\n",
> > +			 __func__, task->comm, task->pid);
> > +		break;
> > +	case -EINVAL:
> > +		pr_debug("%s: %s:%d has an unreliable stack\n",
> > +			 __func__, task->comm, task->pid);
> > +		break;
> > +	case -EADDRINUSE:
> > +		pr_debug("%s: %s:%d is sleeping on function %s\n",
> > +			 __func__, task->comm, task->pid, old_name);
> > +		break;
> 
> I would prefer to be on the safe side and catch error codes that might
> eventually appear in the future.
> 
> 	case 0:
> 		/* success */
> 		break;

	case -EAGAIN:
		/* task_try_func() raced */
		break;

> 	default:
> 		pr_debug("%s: Unknown error code (%d) when trying to switch %s:%d\n",
> 			 __func__, ret, task->comm, task->pid);
> 
> >  	}

Done.