errors during umount make SysRq fail

errors during umount make SysRq fail

[Carl-Daniel Hailfinger]

Hi,

having removed an USB disk while umount for it was still running (yes,
that was stupid) I noticed that umount for this device hangs forever in
D state. That would be ok (consequences for user error), however *all*
other umounts I attempt also hang in D state and SysRq-U also hangs,
resulting in a broken system on the next reboot.

I assume the locking against concurrent umount is there to protect
against non-trivial namespace problems and makes sense for normal
umounting, but IIRC SysRq-U is there to ensure consistent filesystems
on the next startup. Would it make sense to allow SysRq-U to break
these locks?

Similar problem exists with SysRq-S. If syncing of one device hangs,
it will never proceed to the next one in the list. I agree that one
is not trivial (stacked devices, loop et al), but can't we make a
best effort to sync at least the physical devices in the machine?
Please don't shoot me for talking about physical devices, I know
there are some really grey areas trying to define that.

Regards,
Carl-Daniel
-- 
http://www.hailfinger.org/

Re: errors during umount make SysRq fail

[Pavel Machek]

Hi!

> having removed an USB disk while umount for it was still running (yes,
> that was stupid) I noticed that umount for this device hangs forever in
> D state. That would be ok (consequences for user error), however

Actually, I do not think that is okay. USB disk removed while you are
unmounted it is quite simple case of disk error. umount should handle
it.
								Pavel
-- 
People were complaining that M$ turns users into beta-testers...
...jr ghea gurz vagb qrirybcref, naq gurl frrz gb yvxr vg gung jnl!

Re: errors during umount make SysRq fail

[Alan Cox]

On Iau, 2004-11-11 at 19:04, Pavel Machek wrote:
> Hi!
> 
> > having removed an USB disk while umount for it was still running (yes,
> > that was stupid) I noticed that umount for this device hangs forever in
> > D state. That would be ok (consequences for user error), however
> 
> Actually, I do not think that is okay. USB disk removed while you are
> unmounted it is quite simple case of disk error. umount should handle
> it.

Nice theory but 2.6.9 has refcount errors in the eh thread and some
other problems that mean this doesn't happen. It ought to be ok in 10rc1
providing all the patches are merged now