[Devel] [PATCH rh7] ploop: io_direct must fsync after fallocate

[Maxim Patlasov]

While handling fallocate(), ext4 firstly calls ext4_update_inode_size(),
then ext4_mark_inode_dirty().  Both update only in-core state. After
fallocate(), ploop updates BAT bypassing vfs layer (submit bio to
underlying block device). Hence, it's possible that BAT is already
updated, but i_size in now written to the disk yet. If a crash happens
in the middle, BAT points beyond end-of-file, i.e. ploop image is
corrupted.

The patch fixes the problem by ordinary fsync(). This is OK because
we fallocate relatively seldom (PLOOP_MAX_PREALLOC=128MB) and also
because no dirty pages to sync (all I/O is direct).

https://jira.sw.ru/browse/PSBM-45326

Signed-off-by: Maxim Patlasov <mpatlasov at virtuozzo.com>
---
 drivers/block/ploop/io_direct.c |    6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/drivers/block/ploop/io_direct.c b/drivers/block/ploop/io_direct.c
index 0c7e0c4..8032999 100644
--- a/drivers/block/ploop/io_direct.c
+++ b/drivers/block/ploop/io_direct.c
@@ -376,6 +376,7 @@ cached_submit(struct ploop_io *io, iblock_t iblk, struct ploop_request * preq,
 	loff_t new_size;
 	loff_t used_pos;
 	bool may_fallocate = io->files.file->f_op->fallocate &&
+		io->files.file->f_op->fsync &&
 		io->files.flags & EXT4_EXTENTS_FL;
 
 	trace_cached_submit(preq);
@@ -404,6 +405,11 @@ try_again:
 				}
 			}
 
+			/* flush new i_size to disk */
+			err = io->files.file->f_op->FOP_FSYNC(io->files.file, 0);
+			if (err)
+				goto end_write;
+
 			io->prealloced_size = prealloc;
 		}