Re: [PATCH, RFC] xfs: fix multi-AG deadlock in xfs_bunmapi

[Christoph Hellwig <hch@lst.de>]

On Tue, Jul 18, 2017 at 11:33:51AM -0700, Darrick J. Wong wrote:
> On Tue, Jul 18, 2017 at 09:27:43PM +0300, Nikolay Borisov wrote:
> > 
> > 
> > On 18.07.2017 21:15, Darrick J. Wong wrote:
> > > On Tue, Jul 18, 2017 at 07:25:45PM +0200, Christoph Hellwig wrote:
> > >> Just like in the allocator we must avoid touching multiple AGs out of
> > >> order when freeing blocks, as freeing still locks the AGF and can cause
> > >> the same AB-BA deadlocks as in the allocation path.
> > >>
> > >> Signed-off-by: Christoph Hellwig <hch@lst.de>
> > >> Reported-by: Nikolay Borisov <n.borisov.lkml@gmail.com>
> > > 
> > > Looks ok, though I wonder what the bug report looked like. :)
> > 
> > https://www.spinics.net/lists/linux-xfs/msg05918.html
> 
> Ah, ok.  That's what I suspected, so I'm glad to have confirmation.

Btw, I found a little bug when rebasing additional bunmapi work on
top of the patch - we need to add a !isrt to the conditional for
the AG check.  But I'll wait for test results from Nikolay before
resending it, as it should not affect normal non-RT setups.