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

[Qiang Yu]

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@xxxxxxxxxxx>
> >
> > 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].