linux-kernel - Re: [PATCH v4 12/22] lib/stackdepot: use read/write lock

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Message-ID: <ZZ_gssjTCyoWjjhP@tassilo>
Date: Thu, 11 Jan 2024 04:36:02 -0800
From: Andi Kleen <ak@...ux.intel.com>
To: Marco Elver <elver@...gle.com>
Cc: Oscar Salvador <osalvador@...e.de>, andrey.konovalov@...ux.dev,
	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>, kasan-dev@...glegroups.com,
	Evgenii Stepanov <eugenis@...gle.com>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org,
	Andrey Konovalov <andreyknvl@...gle.com>
Subject: Re: [PATCH v4 12/22] lib/stackdepot: use read/write lock

> stackdepot is severely limited in what kernel facilities it may use
> due to being used by such low level facilities as the allocator
> itself.

RCU can be done quite low level too (e.g. there is NMI safe RCU)

> 
> I've been suggesting percpu-rwsem here, but looking at it in more
> detail that doesn't work because percpu-rwsem wants to sleep, but
> stackdepot must work in non-sleepable contexts. :-/

Yes something per CPU would work too I suppose. We used to have
big reader spinlocks for this. 

-Andi