linux-kernel - Re: [PATCH v3 3/4] uaccess: Check no rescheduling function is called in unsafe region

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Message-ID: <20190213103553.GO32494@hirez.programming.kicks-ass.net>
Date:   Wed, 13 Feb 2019 11:35:53 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Julien Thierry <julien.thierry@....com>
Cc:     Ingo Molnar <mingo@...nel.org>, linux-kernel@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, mingo@...hat.com,
        catalin.marinas@....com, will.deacon@....com, james.morse@....com,
        hpa@...or.com, valentin.schneider@....com
Subject: Re: [PATCH v3 3/4] uaccess: Check no rescheduling function is called
 in unsafe region

On Tue, Feb 12, 2019 at 09:15:13AM +0000, Julien Thierry wrote:

> >>> diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> >>> index a674c7db..b1bb7e9 100644
> >>> --- a/kernel/sched/core.c
> >>> +++ b/kernel/sched/core.c
> >>> @@ -3289,6 +3289,14 @@ static inline void schedule_debug(struct task_struct *prev)
> >>>  		__schedule_bug(prev);
> >>>  		preempt_count_set(PREEMPT_DISABLED);
> >>>  	}
> >>> +
> >>> +	if (IS_ENABLED(CONFIG_DEBUG_UACCESS_SLEEP) &&
> >>> +	    unlikely(unsafe_user_region_active())) {
> >>> +		printk(KERN_ERR "BUG: scheduling while user_access enabled: %s/%d/0x%08x\n",
> >>> +		       prev->comm, prev->pid, preempt_count());
> >>> +		dump_stack();
> >>> +	}
> >>> +
> >>>  	rcu_sleep_check();
> >>>
> >>>  	profile_hit(SCHED_PROFILING, __builtin_return_address(0));

> I guess I'll drop the might_resched() part of this patch if that sounds
> alright.

I'm still confused by the schedule_debug() part. How is that not broken?