linux-kernel - Re: [PATCH] devres: Freeing the drs after all release() are called

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Date:	Wed, 6 Nov 2013 17:56:46 -0800
From:	Greg KH <gregkh@...uxfoundation.org>
To:	"Liu, Chuansheng" <chuansheng.liu@...el.com>
Cc:	"tj@...nel.org" <tj@...nel.org>,
	"dmitry.torokhov@...il.com" <dmitry.torokhov@...il.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] devres: Freeing the drs after all release() are called

On Thu, Nov 07, 2013 at 01:18:54AM +0000, Liu, Chuansheng wrote:
> Hello,
> 
> > -----Original Message-----
> > From: Tejun Heo [mailto:htejun@...il.com] On Behalf Of tj@...nel.org
> > Sent: Thursday, November 07, 2013 8:52 AM
> > To: Liu, Chuansheng
> > Cc: Greg KH; dmitry.torokhov@...il.com; linux-kernel@...r.kernel.org
> > Subject: Re: [PATCH] devres: Freeing the drs after all release() are called
> > 
> > Hello,
> > 
> > On Thu, Nov 07, 2013 at 12:36:56AM +0000, Liu, Chuansheng wrote:
> > > Yes, I knew I can put the code always like below:
> > > A = devm_kzalloc();
> > > C = devm_kzalloc();
> > > ...
> > > B= devm_request_threaded_irq(isr_handler);
> > >
> > > But, the above is just one simple coding prototype, if there are many calling:
> > > E -- > F -- > D -- >... then to devm_kzalloc().
> > >
> > > To be honest, it will make code too hard to always adapt the rule?
> > > And I trying to find out every potential devm_kzalloc() before irq requesting.
> > 
> > It isn't a good idea to paper over existing bugs from upper layer.
> > You realize that the above code sequence is already buggy during init
> > unless there's something explicitly blocking generation of irqs until
> > init is complete, right?  The right thing to do would be either
> > reordering the operations or wrapping the operation which unblocks irq
> > at the end of init with devres so that irq gets blocked before the
> > rest of release proceeds.
> > 
> > What we must *NOT* do is working around existing bugs in a half-assed
> > way from midlayer.  
> 
> Yes, doing the right order initialization is always right thing.
> But normally when we hit the panic during shutdown/reboot like below:
> PAGE FAULT XXX 0x12345678
> 
> It is really difficult to debug.
> So at least, could we have method to expose these hidden issues?

Have you enabled timer debugging?  I think there's an irq debugging
option as well.

We aren't going to paper over driver bugs by changing the kernel core,
sorry.  Consider this patch dropped.

greg k-h
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