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. > #14 [ffff88272f5af880] kmem_cache_alloc at ffffffff811f484b > #15 [ffff88272f5af8d0] do_blockdev_direct_IO at ffffffff812535b3 > #16 [ffff88272f5afb00] __blockdev_direct_IO at ffffffff81255dc3 > #17 [ffff88272f5afb30] xfs_vm_direct_IO at ffffffffa01fe3fc [xfs] > #18 [ffff88272f5afb90] generic_file_read_iter at ffffffff81198994 > #19 [ffff88272f5afc50] __dta_xfs_file_read_iter_2398 at ffffffffa020c970 [xfs] > #20 [ffff88272f5afcc0] lo_rw_aio at ffffffffa0377042 [loop] > #21 [ffff88272f5afd70] loop_queue_work at ffffffffa0377c3b [loop] > #22 [ffff88272f5afe60] kthread_worker_fn at ffffffff810a8a0c > #23 [ffff88272f5afec0] kthread at ffffffff810a8428 > #24 [ffff88272f5aff50] ret_from_fork at ffffffff81745242
