[dm-devel] [PATCH] direct-io: use GFP_NOIO to avoid deadlock

[Mikulas Patocka]

On Thu, 8 Aug 2019, Matthew Wilcox wrote:

> On Thu, Aug 08, 2019 at 05:50:10AM -0400, Mikulas Patocka wrote:
> > A deadlock with this stacktrace was observed.
> > 
> > The obvious problem here is that in the call chain 
> > xfs_vm_direct_IO->__blockdev_direct_IO->do_blockdev_direct_IO->kmem_cache_alloc 
> > we do a GFP_KERNEL allocation while we are in a filesystem driver and in a 
> > block device driver.
> 
> But that's not the problem.  The problem is the loop driver calls into the
> filesystem without calling memalloc_noio_save() / memalloc_noio_restore().
> There are dozens of places in XFS which use GFP_KERNEL allocations and
> all can trigger this same problem if called from the loop driver.

OK. I'll send a new patch that sets PF_MEMALLOC_NOIO in the loop driver.

Mikulas