linux-kernel - Re: [REPOST PATCH 1/8] fence: dma-buf cross-device synchronization (v17)

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Message-ID: <53A366B3.8020808@zytor.com>
Date:	Thu, 19 Jun 2014 15:39:47 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Greg KH <gregkh@...uxfoundation.org>,
	Daniel Vetter <daniel@...ll.ch>
CC:	Rob Clark <robdclark@...il.com>,
	Maarten Lankhorst <maarten.lankhorst@...onical.com>,
	linux-arch@...r.kernel.org,
	Thomas Hellstrom <thellstrom@...are.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	"dri-devel@...ts.freedesktop.org" <dri-devel@...ts.freedesktop.org>,
	"linaro-mm-sig@...ts.linaro.org" <linaro-mm-sig@...ts.linaro.org>,
	Thierry Reding <thierry.reding@...il.com>,
	Colin Cross <ccross@...gle.com>,
	Sumit Semwal <sumit.semwal@...aro.org>,
	"linux-media@...r.kernel.org" <linux-media@...r.kernel.org>
Subject: Re: [REPOST PATCH 1/8] fence: dma-buf cross-device synchronization
 (v17)

On 06/19/2014 01:01 PM, Greg KH wrote:
> On Thu, Jun 19, 2014 at 09:15:36PM +0200, Daniel Vetter wrote:
>> On Thu, Jun 19, 2014 at 7:00 PM, Greg KH <gregkh@...uxfoundation.org> wrote:
>>>>>> +     BUG_ON(f1->context != f2->context);
>>>>>
>>>>> Nice, you just crashed the kernel, making it impossible to debug or
>>>>> recover :(
>>>>
>>>> agreed, that should probably be 'if (WARN_ON(...)) return NULL;'
>>>>
>>>> (but at least I wouldn't expect to hit that under console_lock so you
>>>> should at least see the last N lines of the backtrace on the screen
>>>> ;-))
>>>
>>> Lots of devices don't have console screens :)
>>
>> Aside: This is a pet peeve of mine and recently I've switched to
>> rejecting all patch that have a BUG_ON, period.
> 
> Please do, I have been for a few years now as well for the same reasons
> you cite.
> 

I'm actually concerned about this trend.  Downgrading things to WARN_ON
can allow a security bug in the kernel to continue to exist, for
example, or make the error message disappear.

I am wondering if the right thing here isn't to have a user (command
line?) settable policy as to how to proceed on an assert violation,
instead of hardcoding it at compile time.

	-hpa


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