linux-kernel - Re: [PATCH] stackdepot: fix stack_depot_save

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Message-ID: <20241122173820.-gmDeqUQ@linutronix.de>
Date: Fri, 22 Nov 2024 18:38:20 +0100
From: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
To: Marco Elver <elver@...gle.com>
Cc: Andrew Morton <akpm@...ux-foundation.org>,
	Andrey Konovalov <andreyknvl@...il.com>,
	Alexander Potapenko <glider@...gle.com>,
	Dmitry Vyukov <dvyukov@...gle.com>,
	Vlastimil Babka <vbabka@...e.cz>,
	Oscar Salvador <osalvador@...e.de>, linux-kernel@...r.kernel.org,
	linux-mm@...ck.org, kasan-dev@...glegroups.com
Subject: Re: [PATCH] stackdepot: fix stack_depot_save_flags() in NMI context

On 2024-11-22 16:39:47 [+0100], Marco Elver wrote:
> Per documentation, stack_depot_save_flags() was meant to be usable from
> NMI context if STACK_DEPOT_FLAG_CAN_ALLOC is unset. However, it still
> would try to take the pool_lock in an attempt to save a stack trace in
> the current pool (if space is available).
> 
> This could result in deadlock if an NMI is handled while pool_lock is
> already held. To avoid deadlock, only try to take the lock in NMI
> context and give up if unsuccessful.
> 
> The documentation is fixed to clearly convey this.
> 
> Link: https://lkml.kernel.org/r/Z0CcyfbPqmxJ9uJH@elver.google.com
> Fixes: 4434a56ec209 ("stackdepot: make fast paths lock-less again")
> Reported-by: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
> Signed-off-by: Marco Elver <elver@...gle.com>

Reviewed-by: Sebastian Andrzej Siewior <bigeasy@...utronix.de>

Sebastian