linux-kernel - Re: [PATCH v2 2/2] bus: mhi: host: Take irqsave lock after TRE is generated

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Message-ID: <6b396b1a-58a7-bf7c-f644-f1bf298a31e0@quicinc.com>
Date:   Fri, 29 Sep 2023 09:25:51 -0600
From:   Jeffrey Hugo <quic_jhugo@...cinc.com>
To:     Qiang Yu <quic_qianyu@...cinc.com>, <mani@...nel.org>
CC:     <mhi@...ts.linux.dev>, <linux-arm-msm@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>, <quic_cang@...cinc.com>,
        <quic_mrana@...cinc.com>, Hemant Kumar <quic_hemantk@...cinc.com>,
        "Lazarus Motha" <quic_lmotha@...cinc.com>
Subject: Re: [PATCH v2 2/2] bus: mhi: host: Take irqsave lock after TRE is
 generated

On 9/24/2023 10:08 PM, Qiang Yu wrote:
> 
> On 9/22/2023 10:50 PM, Jeffrey Hugo wrote:
>> On 9/13/2023 2:47 AM, Qiang Yu wrote:
>>> From: Hemant Kumar <quic_hemantk@...cinc.com>
>>>
>>> Take irqsave lock after TRE is generated to avoid deadlock due to core
>>> getting interrupts enabled as local_bh_enable must not be called with
>>> irqs disabled based on upstream patch.
>>
>> Where is local_bh_enable() being called?  What patch?  What is 
>> upstream of the codebase you submitted this to?  Why is it safe to 
>> call mhi_gen_tre() without the lock?
> 
> This patch is to fix the issue included by  "[PATCH v2 1/2] bus: mhi: 
> host: Add spinlock to protect WP access when queueing TREs". In that 
> patch, we add write_lock_bh/write_unlock_bh in mhi_gen_tre().
> 
> However, before mhi_gen_tre() is invoked, mhi_cntrl->pm_lock is getted, 
> line 1125, and it is a spin lock. So it becomes we want to get and 
> release bh lock after spin lock.  __local_bh_enable_ip is called as part 
> of write_unlock_bh
> 
> and local_bh_enable. When CONFIG_TRACE_IRQFLAGS is enabled, irq will be 
> enabled once __local_bh_enable_ip is called. The commit message is not 
> clear and confusing, will change it in [patch v3].
> 

In addition to clarifying the commit message, I recommend looking at 
adding this to the other patch.  It seems very odd to review a series 
where one patch introduces a known issue, and a following patch corrects 
that issue.  It would be better to not introduce the issue in the first 
place.