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

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Message-ID: <CAKMK7uFa57YjeJCFQhWFr_5cRTTpWxBdJ1qtb5Ojnu-KZpe-Lw@mail.gmail.com>
Date:	Thu, 19 Jun 2014 21:15:36 +0200
From:	Daniel Vetter <daniel@...ll.ch>
To:	Greg KH <gregkh@...uxfoundation.org>
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 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. Except when you can
prove that the kernel will die in the next few lines and there's
nothing you can do about it a WARN_ON is always better - I've wasted
_way_ too much time debugging hard hangs because such a "benign"
BUG_ON ended up eating my irq handler or a spinlock required by such.
Or some other nonsense that makes debugging a royal pita, especially
if your remote debugger consists of a frustrated users staring at a
hung machine.

</rant>

Cheers, Daniel
-- 
Daniel Vetter
Software Engineer, Intel Corporation
+41 (0) 79 365 57 48 - http://blog.ffwll.ch
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