linux-kernel - Re: [PATCH v2] bus: mhi: host: don't free bhie tables during suspend/hibernation

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Message-ID: <cfb3sntvqhupyhm2m5tevpsl77r6mzl2aqzr3wtxvr22bezmp3@qjh7ftr2kdjy>
Date: Fri, 25 Apr 2025 13:02:51 +0530
From: Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>
To: Muhammad Usama Anjum <usama.anjum@...labora.com>
Cc: Johannes Berg <johannes@...solutions.net>, 
	Jeff Johnson <jjohnson@...nel.org>, Jeffrey Hugo <quic_jhugo@...cinc.com>, 
	Yan Zhen <yanzhen@...o.com>, Youssef Samir <quic_yabdulra@...cinc.com>, 
	Qiang Yu <quic_qianyu@...cinc.com>, Alex Elder <elder@...nel.org>, 
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>, Kunwu Chan <chentao@...inos.cn>, kernel@...labora.com, 
	mhi@...ts.linux.dev, linux-arm-msm@...r.kernel.org, linux-kernel@...r.kernel.org, 
	linux-wireless@...r.kernel.org, ath11k@...ts.infradead.org
Subject: Re: [PATCH v2] bus: mhi: host: don't free bhie tables during
 suspend/hibernation

On Fri, Apr 25, 2025 at 12:14:39PM +0500, Muhammad Usama Anjum wrote:
> On 4/25/25 12:04 PM, Manivannan Sadhasivam wrote:
> > On Thu, Apr 10, 2025 at 07:56:54PM +0500, Muhammad Usama Anjum wrote:
> >> Fix dma_direct_alloc() failure at resume time during bhie_table
> >> allocation. There is a crash report where at resume time, the memory
> >> from the dma doesn't get allocated and MHI fails to re-initialize.
> >> There may be fragmentation of some kind which fails the allocation
> >> call.
> >>
> > 
> > If dma_direct_alloc() fails, then it is a platform limitation/issue. We cannot
> > workaround that in the device drivers. What is the guarantee that other drivers
> > will also continue to work? Will you go ahead and patch all of them which
> > release memory during suspend?
> > 
> > Please investigate why the allocation fails. Even this is not a device issue, so
> > we cannot add quirks :/
> This isn't a platform specific quirk. We are only hitting it because
> there is high memory pressure during suspend/resume. This dma allocation
> failure can happen with memory pressure on any device.
> 

Yes.

> The purpose of this patch is just to make driver more robust to memory
> pressure during resume.
> 
> I'm not sure about MHI. But other drivers already have such patches as
> dma_direct_alloc() is susceptible to failures when memory pressure is
> high. This patch was motivated from ath12k [1] and ath11k [2].
> 

Even if we patch the MHI driver, the issue is going to trip some other driver.
How does the DMA memory goes low during resume? So some other driver is
consuming more than it did during probe()?

> [1]
> https://lore.kernel.org/all/20240419034034.2842-1-quic_bqiang@quicinc.com/
> [2]
> https://lore.kernel.org/all/20220506141448.10340-1-quic_akolli@quicinc.com/
> 
> What do you think can be the way forward for this patch?
> 

Let's try first to analyze why the memory pressure happens during suspend. As I
can see, even if we fix the MHI driver, you are likely to hit this issue
somewhere else.

- Mani

> > 

[...]

> > Did you intend to leak this information? If not, please remove it from
> > stacktrace.
> The device isn't private. Its fine.
> 

Okay.

- Mani

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