linux-kernel - Re: [PATCH RFC v6 05/26] nova-core: mm: Add support to use PRAMIN windows to write to VRAM

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Message-Id: <DG0MXC1R8IRS.Y5X6XDUBOGR5@kernel.org>
Date: Thu, 29 Jan 2026 01:09:21 +0100
From: "Danilo Krummrich" <dakr@...nel.org>
To: "Joel Fernandes" <joelagnelf@...dia.com>
Cc: "Zhi Wang" <zhiw@...dia.com>, <linux-kernel@...r.kernel.org>, "Maarten
 Lankhorst" <maarten.lankhorst@...ux.intel.com>, "Maxime Ripard"
 <mripard@...nel.org>, "Thomas Zimmermann" <tzimmermann@...e.de>, "David
 Airlie" <airlied@...il.com>, "Simona Vetter" <simona@...ll.ch>, "Jonathan
 Corbet" <corbet@....net>, "Alex Deucher" <alexander.deucher@....com>,
 "Christian Koenig" <christian.koenig@....com>, "Jani Nikula"
 <jani.nikula@...ux.intel.com>, "Joonas Lahtinen"
 <joonas.lahtinen@...ux.intel.com>, "Rodrigo Vivi" <rodrigo.vivi@...el.com>,
 "Tvrtko Ursulin" <tursulin@...ulin.net>, "Huang Rui" <ray.huang@....com>,
 "Matthew Auld" <matthew.auld@...el.com>, "Matthew Brost"
 <matthew.brost@...el.com>, "Lucas De Marchi" <lucas.demarchi@...el.com>,
 "Thomas Hellstrom" <thomas.hellstrom@...ux.intel.com>, "Helge Deller"
 <deller@....de>, "Alice Ryhl" <aliceryhl@...gle.com>, "Miguel Ojeda"
 <ojeda@...nel.org>, "Alex Gaynor" <alex.gaynor@...il.com>, "Boqun Feng"
 <boqun.feng@...il.com>, "Gary Guo" <gary@...yguo.net>, "Bjorn Roy Baron"
 <bjorn3_gh@...tonmail.com>, "Benno Lossin" <lossin@...nel.org>, "Andreas
 Hindborg" <a.hindborg@...nel.org>, "Trevor Gross" <tmgross@...ch.edu>,
 "John Hubbard" <jhubbard@...dia.com>, "Alistair Popple"
 <apopple@...dia.com>, "Timur Tabi" <ttabi@...dia.com>, "Edwin Peer"
 <epeer@...dia.com>, "Alexandre Courbot" <acourbot@...dia.com>, "Andrea
 Righi" <arighi@...dia.com>, "Andy Ritger" <aritger@...dia.com>, "Alexey
 Ivanov" <alexeyi@...dia.com>, "Balbir Singh" <balbirs@...dia.com>, "Philipp
 Stanner" <phasta@...nel.org>, "Elle Rhumsaa" <elle@...thered-steel.dev>,
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 <nouveau@...ts.freedesktop.org>, <dri-devel@...ts.freedesktop.org>,
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 <intel-xe@...ts.freedesktop.org>, <linux-fbdev@...r.kernel.org>
Subject: Re: [PATCH RFC v6 05/26] nova-core: mm: Add support to use PRAMIN
 windows to write to VRAM

On Wed Jan 28, 2026 at 4:27 PM CET, Joel Fernandes wrote:
> I will go over these concerns, just to clarify - do you mean forbidding 
> *any* lock or do you mean only forbidding non-atomic locks? I believe we 
> can avoid non-atomic locks completely - actually I just wrote a patch 
> before I read this email to do just. If we are to forbid any locking at 
> all, that might require some careful redesign to handle the above race 
> afaics.

It's not about the locks themselves, sleeping locks are fine too. It's about
holding locks that are held elsewhere when doing memory allocations that can
call back into MMU notifiers or the shrinker.

I.e. if in the fence signalling critical path you wait for a mutex that is held
elsewhere while allocating memory and the memory allocation calls back into the
shrinker, you may end up waiting for your own DMA fence to be signaled, which
causes a deadlock.