linux-kernel - Re: [PATCH AUTOSEL 6.6 14/17] um: virt-pci: don't use kmalloc()

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Message-ID: <c993aa3a8e86e429d2135974929283a33d0f34ca.camel@sipsolutions.net>
Date: Wed, 19 Feb 2025 08:42:01 +0100
From: Johannes Berg <johannes@...solutions.net>
To: Sasha Levin <sashal@...nel.org>, linux-kernel@...r.kernel.org, 
	stable@...r.kernel.org
Cc: Richard Weinberger <richard@....at>, anton.ivanov@...bridgegreys.com, 
	mst@...hat.com, jiri@...nulli.us, tglx@...utronix.de,
 viro@...iv.linux.org.uk, 	krzysztof.kozlowski@...aro.org,
 herve.codina@...tlin.com, 	linux-um@...ts.infradead.org
Subject: Re: [PATCH AUTOSEL 6.6 14/17] um: virt-pci: don't use kmalloc()

On Tue, 2025-02-18 at 15:27 -0500, Sasha Levin wrote:
> From: Johannes Berg <johannes.berg@...el.com>
> 
> [ Upstream commit 5b166b782d327f4b66190cc43afd3be36f2b3b7a ]
> 
> This code can be called deep in the IRQ handling, for
> example, and then cannot normally use kmalloc(). Have
> its own pre-allocated memory and use from there instead
> so this doesn't occur. Only in the (very rare) case of
> memcpy_toio() we'd still need to allocate memory.

I don't believe this patch, "um: convert irq_lock to raw spinlock" and
"um: virtio_uml: use raw spinlock", are relevant to anything older than
6.12. I don't see how applying them would _hurt_, but I didn't have them
before 6.12 and had no lockdep complaints about it; I believe some other
internal IRQ rework caused the issues to pop up.

Never mind that we (Intel WiFi stuff) are probably the only ones ever
running this virtio_uml/virt-pci with lockdep :)

johannes