linux-kernel - Re: [PATCH 0.5/3] livepatch: Convert stack entries array to percpu

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Date:   Tue, 14 Mar 2023 17:26:08 -0700
From:   Josh Poimboeuf <jpoimboe@...nel.org>
To:     Petr Mladek <pmladek@...e.com>
Cc:     live-patching@...r.kernel.org, linux-kernel@...r.kernel.org,
        Seth Forshee <sforshee@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Song Liu <song@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Joe Lawrence <joe.lawrence@...hat.com>,
        Miroslav Benes <mbenes@...e.cz>,
        Jiri Kosina <jikos@...nel.org>, Ingo Molnar <mingo@...hat.com>,
        Rik van Riel <riel@...riel.com>
Subject: Re: [PATCH 0.5/3] livepatch: Convert stack entries array to percpu

On Tue, Mar 14, 2023 at 11:50:21AM +0100, Petr Mladek wrote:
> >  static int klp_check_stack(struct task_struct *task, const char **oldname)
> >  {
> > -	static unsigned long entries[MAX_STACK_ENTRIES];
> > +	unsigned long *entries = this_cpu_ptr(klp_stack_entries);
> >  	struct klp_object *obj;
> >  	struct klp_func *func;
> >  	int ret, nr_entries;
> >  
> > -	ret = stack_trace_save_tsk_reliable(task, entries, ARRAY_SIZE(entries));
> > +	/* Protect 'klp_stack_entries' */
> > +	lockdep_assert_preemption_disabled();
> 
> I think about adding:
> 
> 	/*
> 	 * Stay on the safe side even when cond_resched() is called from
> 	 * an IRQ context by mistake.
> 	 */
> 	if (!in_task())
> 		return -EINVAL;
> 
> Or is this prevented another way, please?

An IRQ handler trying to schedule would be a pretty major bug, no?

I think there are already several different checks for that.  For
example, the __might_resched() call in cond_resched().

-- 
Josh