These rules have been hidden in several if-else and are not
straightforward to follow, for example, dio submit hook's nocsum case
has a bug , i.e. doing async submit instead of sync submit, which has
been fixed recently.
This is documenting the rules for reference.
Signed-off-by: Liu Bo <bo.li....@oracle.com>
---
fs/btrfs/inode.c | 17 ++++++++++++++++-
1 file changed, 16 insertions(+), 1 deletion(-)
diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
index e9a827b..9a2bdd9 100644
--- a/fs/btrfs/inode.c
+++ b/fs/btrfs/inode.c
@@ -1962,7 +1962,21 @@ static blk_status_t __btrfs_submit_bio_done(void
*private_data, struct bio *bio,
/*
* extent_io.c submission hook. This does the right thing for csum calculation
- * on write, or reading the csums from the tree before a read
+ * on write, or reading the csums from the tree before a read.
+ *
+ * Rules about async/sync submit,
+ * a) read: sync submit
+ *
+ * b) write without checksum: sync submit
+ *
+ * c) write with checksum:
+ * c-1) if bio is issued by fsync: sync submit
+ * (sync_writers != 0)
+ *
+ * c-2) if root is reloc root: sync submit
+ * (only in case of buffered IO)
+ *
+ * c-3) otherwise: async submit
*/
static blk_status_t btrfs_submit_bio_hook(void *private_data, struct bio *bio,
int mirror_num, unsigned long bio_flags,
@@ -8549,6 +8563,7 @@ __btrfs_submit_dio_bio(struct bio *bio, struct inode
*inode, u64 file_offset,
bool write = bio_op(bio) == REQ_OP_WRITE;
blk_status_t ret;
+ /* Check btrfs_submit_bio_hook() for rules about async submit. */
if (async_submit)
async_submit = !atomic_read(&BTRFS_I(inode)->sync_writers);
--
2.9.4
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