linux-ext4 - Re: [PATCH 1/2] ext4: call WARN

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Message-ID: <20130125150948.GK28908@thunk.org>
Date:	Fri, 25 Jan 2013 10:09:48 -0500
From:	Theodore Ts'o <tytso@....edu>
To:	Lukáš Czerner <lczerner@...hat.com>
Cc:	linux-ext4@...r.kernel.org
Subject: Re: [PATCH 1/2] ext4: call WARN_ON after the debug message

On Fri, Jan 25, 2013 at 10:22:44AM +0100, Lukáš Czerner wrote:
> 
> we can get the EIO error from ext4_map_blocks not only in the case
> of hardware error. The extent tree might not be in consistent state,
> or we could even ask for blocks outside the file system itself (I
> believe I've seen this before) and I think that in those cases it
> might be worth to all WARN_ON.

Sure, but in those cases, the file system is corrupt, and we should
have thrown an ext4_error() in ext4_map_blocks().  The point is that a
WARN_ON is only useful if there is a potential programming bug.  If we
know for sure that it's caused by a file system corruption, then we
don't want to throw a WARN_ON.

Even if there is a kerneloops.org replacement --- in fact, especially
if there is kerneloops.org replacement --- we only want to throw
WARN_ON's in cases where it's just a pedestrian file system
corruption.  Otherwise we'll end up wasting a lot of time chasing down
something which was caused by a hardware error, and needing to calm
down users (and breathless, spectacularizing, irresponsible journalism
from web sites such as Phoronix).

					- Ted
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