linux-kernel - Re: [PATCH] kasan: Remove kasan_record_aux_stack

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Message-ID: <20241122152905.iyjG97GS@linutronix.de>
Date: Fri, 22 Nov 2024 16:29:05 +0100
From: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
To: Marco Elver <elver@...gle.com>
Cc: Andrey Konovalov <andreyknvl@...il.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Vlastimil Babka <vbabka@...e.cz>,
	syzbot <syzbot+39f85d612b7c20d8db48@...kaller.appspotmail.com>,
	Liam.Howlett@...cle.com, akpm@...ux-foundation.org,
	jannh@...gle.com, linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	lorenzo.stoakes@...cle.com, syzkaller-bugs@...glegroups.com,
	kasan-dev <kasan-dev@...glegroups.com>,
	Andrey Ryabinin <ryabinin.a.a@...il.com>,
	Alexander Potapenko <glider@...gle.com>,
	Waiman Long <longman@...hat.com>, dvyukov@...gle.com,
	vincenzo.frascino@....com, paulmck@...nel.org, frederic@...nel.org,
	neeraj.upadhyay@...nel.org, joel@...lfernandes.org,
	josh@...htriplett.org, boqun.feng@...il.com, urezki@...il.com,
	rostedt@...dmis.org, mathieu.desnoyers@...icios.com,
	jiangshanlai@...il.com, qiang.zhang1211@...il.com, mingo@...hat.com,
	juri.lelli@...hat.com, vincent.guittot@...aro.org,
	dietmar.eggemann@....com, bsegall@...gle.com, mgorman@...e.de,
	vschneid@...hat.com, tj@...nel.org, cl@...ux.com,
	penberg@...nel.org, rientjes@...gle.com, iamjoonsoo.kim@....com,
	Thomas Gleixner <tglx@...utronix.de>, roman.gushchin@...ux.dev,
	42.hyeyoo@...il.com, rcu@...r.kernel.org
Subject: Re: [PATCH] kasan: Remove kasan_record_aux_stack_noalloc().

On 2024-11-22 16:01:29 [+0100], Marco Elver wrote:
> > Do we need to update the comment saying that it must not be used from
> > NMI or do we make it jump over the locked section in the NMI case?
> 
> Good point. It was meant to also be usable from NMI, because it's very
> likely to succeed, and should just take the lock-less fast path once the
> stack is in the depot.
> 
> But I think we need a fix like this for initial saving of a stack trace:
> 
> 
> diff --git a/lib/stackdepot.c b/lib/stackdepot.c
> index 5ed34cc963fc..245d5b416699 100644
> --- a/lib/stackdepot.c
> +++ b/lib/stackdepot.c
> @@ -630,7 +630,15 @@ depot_stack_handle_t stack_depot_save_flags(unsigned long *entries,
>  			prealloc = page_address(page);
>  	}
>  
> -	raw_spin_lock_irqsave(&pool_lock, flags);
> +	if (in_nmi()) {
> +		/* We can never allocate in NMI context. */
> +		WARN_ON_ONCE(can_alloc);
> +		/* Best effort; bail if we fail to take the lock. */
> +		if (!raw_spin_trylock_irqsave(&pool_lock, flags))
> +			goto exit;
> +	} else {
> +		raw_spin_lock_irqsave(&pool_lock, flags);
> +	}
>  	printk_deferred_enter();
>  
>  	/* Try to find again, to avoid concurrently inserting duplicates. */
> 
> 
> If that looks reasonable, I'll turn it into a patch.

Yes, looks reasonable.

Sebastian