Re: [xfs-masters] Re: freeze vs freezer

[Jeremy Fitzhardinge]

Dave Chinner wrote:
> On Mon, Jun 30, 2008 at 01:22:47AM +0200, Rafael J. Wysocki wrote:
>   
> > On Monday, 30 of June 2008, Dave Chinner wrote:
> >     
> > > On Thu, Jun 26, 2008 at 05:09:10PM +0200, Pavel Machek wrote:
> > >       
> > > > > > Is this the same thing the per-device IO-queue-freeze patches for
> > > > > > HDAPS also
> > > > > > need to do?  If so, you may want to talk to Elias Oltmanns
> > > > > > <eo@xxxxxxxxxxxxxx> about it.  Added to CC.
> > > > > >             
> > > > > Thanks for the heads up Henrique. Even though these issues seem to be
> > > > > related up to a certain degree, there probably are some important
> > > > > differences. When suspending a system, the emphasis is on leaving the
> > > > > system in a consistent state (think of journalled file systems), whereas
> > > > > disk shock protection is mainly concerned with stopping I/O as soon as
> > > > > possible. As yet, I cannot possibly say to what extend these two
> > > > > concepts can be reconciled in the sense of sharing some common code.
> > > > >           
> > > > Actually, I believe requirements are same.
> > > >
> > > > 'don't do i/o in dangerous period'.
> > > >
> > > > swsusp will just do sync() before entering dangerous period. That
> > > > provides consistent-enough state...
> > > >         
> > > As I've said many times before - if the requirement is "don't do
> > > I/O" then you have to freeze the filesystem. In no way does 'sync'
> > > prevent filesystems from doing I/O.....
> > >       
> > Well, it seems we can handle this on the block layer level, by temporarily
> > replacing the elevator with something that will selectively prevent fs I/O
> > from reaching the layers below it.
> >     
>
> Why? What part of freeze_bdev() doesn't work for you?

Well, my original problem - which is still an issue - is that a process 
writing to a frozen XFS filesystem is stuck in D state, and therefore 
cannot be frozen as part of suspend.

   J

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