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: <20260130015901.GA301119@joelbox2>
Date: Thu, 29 Jan 2026 20:59:01 -0500
From: Joel Fernandes <joelagnelf@...dia.com>
To: John Hubbard <jhubbard@...dia.com>
Cc: Danilo Krummrich <dakr@...nel.org>, Zhi Wang <zhiw@...dia.com>,
	linux-kernel@...r.kernel.org,
	Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
	Maxime Ripard <mripard@...nel.org>,
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	Joonas Lahtinen <joonas.lahtinen@...ux.intel.com>,
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	Tvrtko Ursulin <tursulin@...ulin.net>,
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Subject: Re: [PATCH RFC v6 05/26] nova-core: mm: Add support to use PRAMIN
 windows to write to VRAM

On 1/29/26 8:12 PM, John Hubbard wrote:
> On 1/29/26 4:26 PM, Joel Fernandes wrote:
>> Based on the below discussion and research, I came up with some deadlock
>> scenarios that we need to handle in the v6 series of these patches.
>> [...]
>> memory allocations under locks that we need in the dma-fence signaling
>> critical path (when doing the virtual memory map/unmap)
> 
> unmap? Are you seeing any allocations happening during unmap? I don't
> immediately see any, but that sounds surprising.

Not allocations but we are acquiring locks during unmap. My understanding
is (at least some) unmaps have to also be done in the dma fence signaling
critical path (the run stage), but Danilo/you can correct me if I am wrong
on that. We cannot avoid all locking but those same locks cannot be held in
any other paths which do a memory allocation (as mentioned in one of the
deadlock scenarios), that is probably the main thing to check for unmap.

Thanks,
-- 
Joel Fernandes