Might be a good idea to cc Yafang on this ... On Fri, Dec 04, 2020 at 09:12:02AM +1100, Dave Chinner wrote: > On Thu, Dec 03, 2020 at 02:10:56PM +0000, David Howells wrote: > > Hi Christoph, > > > > We're having a problem making the fscache/cachefiles rewrite work with XFS, if > > you could have a look? Jeff Layton just tripped the attached warning from > > this: > > > > /* > > * Given that we do not allow direct reclaim to call us, we should > > * never be called in a recursive filesystem reclaim context. > > */ > > if (WARN_ON_ONCE(current->flags & PF_MEMALLOC_NOFS)) > > goto redirty; > > I've pointed out in other threads where issues like this have been > raised that this check is not correct and was broken some time ago > by the PF_FSTRANS removal. The "NOFS" case here was originally using > PF_FSTRANS to protect against recursion from within transaction > contexts, not recursion through memory reclaim. Doing writeback > from memory reclaim is caught by the preceeding PF_MEMALLOC check, > not this one. > > What it is supposed to be warning about is that writeback in XFS can > start new transactions and nesting transactions is a guaranteed way > to deadlock the journal. IOWs, doing writeback from an active > transaction context is a bug in XFS. > > IOWs, we are waiting on a new version of this patchset to be posted: > > https://lore.kernel.org/linux-xfs/20201103131754.94949-1-laoar.shao@xxxxxxxxx/ > > so that we can get rid of this from iomap and check the transaction > recursion case directly in the XFS code. Then your problem goes away > completely.... > > Cheers, > > Dave. > -- > Dave Chinner > david@xxxxxxxxxxxxx
