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
