Re: [linux-pm] Is it supposed to be ok to call del_gendisk whileuserspace is frozen?

[Pavel Machek]

Hi!

> > > The reason for freezing those tasks is to avoid writebacks at random
> > > times during a system sleep transition, when the underlying device may
> > > already be suspended, right?
> > 
> > It is also there to avoid inconsistency between in-filesystem data and
> > snapshot in hibernation image.
> 
> A good point, although in this case I think it won't matter.  Writing
> out a dirty page twice (once right after taking the snapshot and then
> again after resuming from hibernation) will leave the disk in a correct
> state.

No, I don't think so. Have you considered all the various journalling
systems?

Definitely not in presence of I/O errors. Commit block can only be
written after previous blocks are successfully writen to the journal.

So lets see:

<snapshot>

Write previous block, write commit block, write more blocks

<hibernation powerdown, restart>

Error writing previous block (block now contains garbage), leading to
kernel panic

<restart>

journalling assumptions broken: commit block is there, but previous
blocks are not intact. Data loss.

...and that was the first I could think about. Lets not do
 this. Barriers were invented for a reason.
								Pavel
-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
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