Re: [PATCH] Revert "Btrfs: race free update of commit root for ro snapshots"

[Chris Mason <clm@fb.com>]

On Wed, Oct 15, 2014 at 2:37 PM, Filipe Manana <fdmanana@gmail.com> 
wrote:
> This reverts commit 9c3b306e1c9e6be4be09e99a8fe2227d1005effc.
> 
> Switching only one commit root during a transaction is wrong because 
> it leads
> the fs into an inconsistent state. All commit roots should be 
> switched at once,
> at transaction commit time, otherwise backref walking can often miss 
> important
> references that were only accessible through the old commit root.
> Plus, the root item for the snapshot's root wasn't getting updated 
> and preventing
> the next transaction commit to do it.
> 
> This made several users get into random corruption issues after 
> creation of
> readonly snapshots.

Thanks Filipe and everyone else that helped nail this down.  I 
convinced myself that working on readonly roots made the original 
commit ok, but clearly I was horribly wrong.  Sorry guys, I'll get this 
off to Linus as soon as I do a quick cook here.

-chris