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

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Message-ID: <Z9TX7vadBvxcrbf9@lappy>
Date: Fri, 14 Mar 2025 21:29:18 -0400
From: Sasha Levin <sashal@...nel.org>
To: Johannes Berg <johannes@...solutions.net>
Cc: linux-kernel@...r.kernel.org, stable@...r.kernel.org,
	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 Wed, Feb 19, 2025 at 08:42:01AM +0100, Johannes Berg wrote:
>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 :)

I'll drop it, thanks!

-- 
Thanks,
Sasha