[PATCH] xfs: fix bogus space reservation in xfs_iomap_write_allocate

[Christoph Hellwig]

On Fri, Aug 05, 2016 at 10:03:54AM +1000, Dave Chinner wrote:
> I don't think this part of the fix is correct. nres feeds into
> args->total which is then used during the AGFL fixup checks. If this
> is not set correctly, then we'll select AGs we have enough space in
> the AG to fix up the AGFL, but not enough space to allocate all the
> BMBT blocks we require. That then leads to ABBA deadlocks on AGF
> locks near ENOSPC - see commit dbd5c8c ("xfs: pass total block
> res. as total xfs_bmapi_write() parameter") for the full details.

I've been going forth and back between both versions and both have
tested fine - I couldn't really convince me which one is more correct.

> I've been testing a local version of this fix since you pointed out
> the problem that still passed nres into xfs_bmapi_write() and I
> haven't seen any problems, so I think it is correct to keep nres
> here. I'm going to drop this hunk from this patch for the moment in
> my tree.

Ok, sounds fine.  If you want a real resend let me know.