linux-kernel - Re: [PATCH] Silence 'ignoring return value' warnings in drivers/video/aty/radeon

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Date:	Wed, 07 May 2008 14:33:24 +1000
From:	Benjamin Herrenschmidt <benh@...nel.crashing.org>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	David Miller <davem@...emloft.net>, tony@...eyournoodle.com,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] Silence 'ignoring return value' warnings in
	drivers/video/aty/radeon_base.c


On Tue, 2008-05-06 at 18:20 -0700, Andrew Morton wrote:
> Look at the history of this.  A couple of years ago we were seeing a huge
> number of mysterious crashes and warnings in and around sysfs and driver
> code and we just didn't have a clue what was causing it, because those
> crashes were happening long, long after the buggy code had done its work.
> 
> So I went in there and found a tremendous amount of code in driver core,
> sysfs and in callers of both which was just ignoring error returns and
> blundering on.
> 
> It was a comnplete undebuggable unmaintainable mess.  And the reason why it
> was undebuggable was because the code was failing to detect errors *when
> they occurred*.  So we (me, Cornelia, Greg, others) set about fixing all of
> that.  And to support that effort we marked all the things which should be
> checked with __must_check.

You haven't read me properly. I'm not advocating completely ignoring
those errors. In fact, I'm all about keeping must check on things like
allocations. However, in cases like sysfs_create_file() like many
similar things where failure will -not- prevent proper operations of the
driver or subsystem, mostly only compromise the user ABI, I believe it's
a _LOT_ more efficient to put -one- printk in the function itself,
rather than all callers

> Now you come along and cherrypick a few callsites where you'd rather not
> bother checking and assert that the entire effort was wrong-headed.  Well
> sorry, no, it wasn't.  Sure, there's a little bit of undesirable fallout
> but the whole thing had.  to.  be.  done.

Of course the whole effort was not wrong headed. I'm really only
complaining about all those stupid sysfs_create_file() and maybe a
handful of similar ones.

Ben.


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