[PATCH v4 2/7] nvdimm: virtio_pmem: use GFP_NOIO for child flush bio

[Li Chen <me@linux.beauty>]

async_pmem_flush() can allocate a child flush bio from filesystem flush
and writeback paths. GFP_ATOMIC is unnecessarily restrictive there and can
make the allocation fail under pressure, which then propagates -ENOMEM to
the flush caller.

A local virtio-pmem mkfs sanity test hit a flush failure before this
change:

  wipefs: /dev/pmem0: cannot flush modified buffers: Input/output error
  mkfs.ext4: Input/output error while writing out and closing file system
  nd_region region0: dbg: nvdimm_flush rc=-5

The debug log showed async_pmem_flush() was entered and nvdimm_flush()
returned -EIO. With GFP_NOIO, the same test reached mkfs_rc=0, mount_rc=0,
and umount_rc=0.

Use GFP_NOIO instead. The path may sleep, but it must not recurse into
filesystem I/O reclaim while it is already servicing a flush request.

Signed-off-by: Li Chen <me@linux.beauty>
---
v3->v4:
- New patch.

 drivers/nvdimm/nd_virtio.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/nvdimm/nd_virtio.c b/drivers/nvdimm/nd_virtio.c
index 4176046627beb..081370aac6317 100644
--- a/drivers/nvdimm/nd_virtio.c
+++ b/drivers/nvdimm/nd_virtio.c
@@ -117,7 +117,7 @@ int async_pmem_flush(struct nd_region *nd_region, struct bio *bio)
 	if (bio && bio->bi_iter.bi_sector != -1) {
 		struct bio *child = bio_alloc(bio->bi_bdev, 0,
 					      REQ_OP_WRITE | REQ_PREFLUSH,
-					      GFP_ATOMIC);
+					      GFP_NOIO);
 
 		if (!child)
 			return -ENOMEM;
-- 
2.52.0