linux-ext4 - Re: Weird I/O errors with USB hard drive not remounting filesystem readonly

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Date:	Mon, 23 Nov 2009 15:06:05 -0500
From:	tmhikaru@...il.com
To:	Jan Kara <jack@...e.cz>
Cc:	linux-kernel@...r.kernel.org, linux-usb@...r.kernel.org,
	Jens Axboe <axboe@...nel.dk>, linux-scsi@...r.kernel.org,
	linux-ext4@...r.kernel.org
Subject: Re: Weird I/O errors with USB hard drive not remounting filesystem readonly

On Mon, Nov 23, 2009 at 02:50:22PM -0500, tm@ wrote:
> On Mon, Nov 23, 2009 at 07:54:50PM +0100, Jan Kara wrote:
> > On Mon 23-11-09 13:20:26, Alan Stern wrote:
> > > On Mon, 23 Nov 2009, Jan Kara wrote:
> > > 
> > > > On Mon 23-11-09 10:06:03, Alan Stern wrote:
> > > > > On Mon, 23 Nov 2009, Jan Kara wrote:
> > > > > 
> > > > > >   Yeah, from what you write, it looks like USB enclosure is at fault (or it
> > > > > > could still be your USB controller but I doubt it).  It's still a bit
> > > > > > bothering that the error reported by the drive was not properly propagated
> > > > > > up to VFS. Either it's some block layer retry/ignore magic that I missed or
> > > > > > we ignore errors from block layer in some place.
> > > > > 
> > > > > Is there any interest in tracking this down?  It's not hard to find out
> > > > > what low-level errors are being reported and to generate them on demand
> > > > > with an emulated USB disk drive.
> > > >   Well, if you could provide me with the patch, I could try to track down
> > > > why the errors aren't propagated... It would be interesting because if it's
> > > > not some retry logic in block layer, it's a bug in VFS ;).
> > > 
> > > I can't provide a patch without first knowing what the errors are.  The 
> > > way to find out is to use usbmon.  See Documentation/usb/usbmon.txt for 
> > > instructions.
> >   Ah, OK. The problem manifests itself as an error in SATA communication
> > (which in fact somehow happens over USB, but I don't really know the
> > details of mass storage over USB) so debugging USB would become actual only
> > if we found out it's really some bug in an usb stack. But so far the most
> > probable is just an error somewhere between the USB controller in the
> > enclosure and the drive itself. BTW: Is the data transferred over USB
> > checksummed?
> > 
> > 									Honza
> 	Mind that this is an ide hard drive in a usb enclosure, not sata.
> The error reported is bizzare. I don't know if I'll be able to get the
> enclosure to cause the error on demand, but before I try supergluing it,
> I'll try to do whatever I need to do with usbmon so we can get the error
> that's actually happening so you can do whatever you need to do to track it
> down :)
> 
> Tim McGrath
Uhh, this could be a problem. CONFIG_USB_MON=y is set in my .config BUT,
although I followed the directions and debugfs is mounted,

root@...l:/home/tm# mount
/dev/root on / type ext4 (rw,relatime,barrier=1,data=ordered,data_err=abort)
proc on /proc type proc (rw)
sysfs on /sys type sysfs (rw)
usbfs on /proc/bus/usb type usbfs (rw)
none_debugs on /sys/kernel/debug type debugfs (rw)

I receive this message when I test if usbmon's directory exists:

root@...l:/home/tm# ls /sys/kernel/debug/usbmon
ls: cannot access /sys/kernel/debug/usbmon: No such file or directory

According to the kernel documentation usbmon should be loaded already. Help?

Timothy McGrath
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