linux-kernel - RE: [PATCH v2] acpi/ghes: Prevent sleeping with spinlock held

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Date: Wed, 21 Feb 2024 11:57:44 -0800
From: Dan Williams <dan.j.williams@...el.com>
To: Ira Weiny <ira.weiny@...el.com>, Dan Williams <dan.j.williams@...el.com>,
	"Rafael J. Wysocki" <rafael@...nel.org>, Jonathan Cameron
	<jonathan.cameron@...wei.com>, Smita Koralahalli
	<Smita.KoralahalliChannabasappa@....com>
CC: <linux-acpi@...r.kernel.org>, <linux-cxl@...r.kernel.org>,
	<linux-kernel@...r.kernel.org>, Dan Carpenter <dan.carpenter@...aro.org>,
	"Ira Weiny" <ira.weiny@...el.com>
Subject: RE: [PATCH v2] acpi/ghes: Prevent sleeping with spinlock held

Ira Weiny wrote:
> Dan Williams wrote:
> > Ira Weiny wrote:
> 
> [snip]
> 
> > >  
> > > -	guard(rwsem_read)(&cxl_cper_rw_sem);
> > > -	if (cper_callback)
> > > -		cper_callback(event_type, rec);
> > 
> > Given a work function can be set atomically there is no need to create /
> > manage a registration lock. Set a 'struct work' instance to a CXL
> > provided routine on cxl_pci module load and restore it to a nop function
> > + cancel_work_sync() on cxl_pci module exit.
> 
> Ok I'll look into this.
> 
> > 
> > > +	wi = kmalloc(sizeof(*wi), GFP_ATOMIC);
> > 
> > The system is already under distress trying to report an error it should
> > not dip into emergency memory reserves to report errors. Use a kfifo()
> > similar to how memory_failure_queue() avoids memory allocation in the
> > error reporting path.
> 
> I have a question on ghes_proc() [ghes_do_proc()].  Can they be called by
> 2 threads at the same time?  It seems like there could be multiple
> platform devices which end up queueing into the single kfifo.

Yes, that is already the case for memory_failure_queue() and
aer_recover_queue().

> there needs to be a kfifo per device or synchronization with multiple
> writers.

Yes, follow the other _queue() examples. kfifo_in_spinlocked() looks
useful for this purpose.

I expect no lock needed on the read side since the reader is only the
single workqueue context.