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

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Message-ID: <ZbE5tBBjlhz3JN5+@gmail.com>
Date: Wed, 24 Jan 2024 08:24:20 -0800
From: Breno Leitao <leitao@...ian.org>
To: Marco Elver <elver@...gle.com>
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, Jan 24, 2024 at 03:21:26PM +0100, Marco Elver wrote:
> 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?

That is true. I will retest and let you know if it is still
reproducible.

Thanks.