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

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Date: Wed, 24 Jan 2024 15:21:26 +0100
From: Marco Elver <elver@...gle.com>
To: Breno Leitao <leitao@...ian.org>
Cc: 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>, Oscar Salvador <osalvador@...e.de>, 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

On Wed, 24 Jan 2024 at 15:16, Breno Leitao <leitao@...ian.org> wrote:
>
> Hello Andrey,
>
> On Mon, Nov 20, 2023 at 06:47:10PM +0100, andrey.konovalov@...ux.dev wrote:
> > From: Andrey Konovalov <andreyknvl@...gle.com>
> >
> > Currently, stack depot uses the following locking scheme:
> >
> > 1. Lock-free accesses when looking up a stack record, which allows to
> >    have multiple users to look up records in parallel;
> > 2. Spinlock for protecting the stack depot pools and the hash table
> >    when adding a new record.
> >
> > For implementing the eviction of stack traces from stack depot, the
> > lock-free approach is not going to work anymore, as we will need to be
> > able to also remove records from the hash table.
> >
> > Convert the spinlock into a read/write lock, and drop the atomic accesses,
> > as they are no longer required.
> >
> > Looking up stack traces is now protected by the read lock and adding new
> > records - by the write lock. One of the following patches will add a new
> > function for evicting stack records, which will be protected by the write
> > lock as well.
> >
> > With this change, multiple users can still look up records in parallel.
> >
> > This is preparatory patch for implementing the eviction of stack records
> > from the stack depot.
>
> I am testing quite recent "debug" kernel (with KASAN, Lockdep, etc
> enabled). This kernel is based on
> 9f8413c4a66f2fb776d3dc3c9ed20bf435eb305e, and I found the following

This version predates this series, as far as I can tell. Can you try linux-next?

Thanks,
-- Marco