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Date:	Thu, 19 Jun 2014 21:15:36 +0200
From:	Daniel Vetter <>
To:	Greg KH <>
Cc:	Rob Clark <>,
	Maarten Lankhorst <>,,
	Thomas Hellstrom <>,
	Linux Kernel Mailing List <>,
	"" <>,
	"" <>,
	Thierry Reding <>,
	Colin Cross <>,
	Sumit Semwal <>,
	"" <>
Subject: Re: [REPOST PATCH 1/8] fence: dma-buf cross-device synchronization (v17)

On Thu, Jun 19, 2014 at 7:00 PM, Greg KH <> 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.


Cheers, Daniel
Daniel Vetter
Software Engineer, Intel Corporation
+41 (0) 79 365 57 48 -
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