Re: Error handling: How to "lose" a transaction

[Chris Mason <chris.mason@oracle.com>]

On Fri, Dec 23, 2011 at 12:12:31AM -0500, Jeff Mahoney wrote:
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> On 12/21/2011 10:38 PM, Jeff Mahoney wrote:
> > On 12/21/2011 10:21 PM, Liu Bo wrote:
> >> On 12/22/2011 10:59 AM, Jeff Mahoney wrote: Sorry I haven't 
> >> responded to this yet. I started digging right in and I've
> >> started to have some good results. It turns out there's already a
> >>  btrfs_cleanup_transaction call that will tear down outstanding 
> >> transactions. It's not perfect and I've fixed a few bugs in
> >> there, but it saved me a bunch of effort. I just wished I noticed
> >> it a day before since I had it half implemented myself. :)
> > 
> > 
> >>> Hi Jeff,
> > 
> >>> Yes, it should be, and I wrote this cleanup_transaction where
> >>> I should notice you earlier... Anyway, thanks for your effort.
> > 
> >>> The error handling part has lots of corner cases, so I just
> >>> pick up a brute way to tear down the current transaction in
> >>> order to make the FS RO.
> > 
> > Oh, and it's worked great. The brute force method is a good start
> > and will address the most severe problems (and most cases) well.
> > I've decided to ignore most cases of -ENOMEM for now. The biggest
> > bug I ran into so far was calling mutex_lock while holding a
> > spinlock. It was a quick fix.
> > 
> > The method I've generally used is to mark the transaction aborted
> > and pass the error up as quickly as possible, cleaning up the
> > local allocations and locks as I go. The transaction gets
> > completed normally, returns an error, isn't committed, and then is
> > destroyed (with others, potentially) when called from in 
> > btrfs_commit_transaction. Btrfs makes this super easy since we can 
> > just skip all the CoW writes.
> 
> 
> Now, just out of curiosity, would it be ok if I printed this when we
> ran out memory in deep call paths?
> 
>      FAIL WHALE!
> 
> W     W      W
> W        W  W     W
>               '.  W
>   .-""-._     \ \.--|
>  /       "-..__) .-'
> |     _         /
> \'-.__,   .__.,'
>  `'----'._\--'
> VVVVVVVVVVVVVVVVVVVVV
> 
> 
> Happy Holidays ;)

I'll take any patch you put into the suse kernel ;)

-chris