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

From: Pavel Machek
Date: Wed Mar 03 2010 - 16:51:18 EST


> > > 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

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:


Write previous block, write commit block, write more blocks

<hibernation powerdown, restart>

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


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.
(cesky, pictures)
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