linux-kernel - Re: Bug#502583: scary messages in dmesg

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Date:	Tue, 21 Oct 2008 12:35:00 -0200
From:	Rogério Brito <rbrito@....usp.br>
To:	Theodore Tso <tytso@....edu>,
	Alexandre Lymberopoulos <lymber@...il.com>,
	502583@...s.debian.org, 502583-submitter@...s.debian.org,
	linux-kernel@...r.kernel.org, rafael@...ian.org
Subject: Re: Bug#502583: scary messages in dmesg

First of all, Thanks Theodore.

On Oct 21 2008, Theodore Tso wrote:
> On Tue, Oct 21, 2008 at 08:15:10AM -0200, Rogério Brito wrote:
> > Did you sync the device? From the message, it seems that some data were
> > to be written to the device, but the device was already gone by that
> > time, but I'm not a specialist on the filesystem subsystem and perhaps
> > others could say more about it.
> 
> A patch to suppress the WARN information will be in 2.6.28 when the
> user does something stupid (i.e., yank out a USB stick without
> unmounting the filesystem first).

Right. I will put a big, fat warning on the installation of usbmount and
tell the users about it. Besides that, depending on the filesystem, the
superblock may be marked as dirty.

> This was done mainly to suppress the "scary message" in dmesg, which on
> distributions that support uploading such messages to
> http://www.kerneloops.org for analysis, was cluttering the reports.

Right...

> > > > [39071.160167] Buffer I/O error on device sda1, logical block 1545
> > > > [39071.160170] lost page write due to I/O error on sda1
> > > > [39071.160184] Buffer I/O error on device sda1, logical block 1545
> > > > [39071.160187] lost page write due to I/O error on sda1
> 
> These errors you'd still get, since these messages are the sound of
> users' data being irretrivably being lost.

Good that not all messages will be going... BTW, this reminded me of a
patch that eliminated a whole lot of messages (BUG()'s) for embedded
devices... I didn't find it anymore...

Also, the same thing with the hash tables that could turn into linked lists
eventually...

But I'm drifting away from the main topic.

> > Well, it is a bug. It just needs more investigation to see where the bug
> > lies.
> 
> I don't know if you would call it a bug or not.  Fundamentally,
> yanking out a USB stick without unmounting it first is dangerous, and
> can lead to data loss.

At least sync'ing...

[snip]

> If you see "lost page write due to I/O error", then you will have lost
> data due to premature removal of the USB stick, and fundamentally
> *that* bug exists between the keyboard and the chair.

Ok, so I'm closing this bug in the next upload.


Thanks, Rogério Brito.

-- 
Rogério Brito : rbrito@...ckenzie,ime.usp}.br : GPG key 1024D/7C2CAEB8
http://www.ime.usp.br/~rbrito : http://meusite.mackenzie.com.br/rbrito
Projects: algorithms.berlios.de : lame.sf.net : vrms.alioth.debian.org
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