From 4c274bc67b8104c6aff89b4176395e368e8c231c Mon Sep 17 00:00:00 2001 From: Liu Bo Date: Wed, 1 Nov 2017 17:19:27 -0600 Subject: [PATCH] Btrfs: document rules about bio async submit 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 Signed-off-by: David Sterba --- 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 c8a3e84d7114fa..f259d89804b25c 100644 --- a/fs/btrfs/inode.c +++ b/fs/btrfs/inode.c @@ -1951,7 +1951,21 @@ 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, @@ -8456,6 +8470,7 @@ __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);