From ac5e666951507ceb1da2ed85c4f5c7bb88bec06e Mon Sep 17 00:00:00 2001 From: Filipe Manana Date: Mon, 4 Jul 2022 12:42:04 +0100 Subject: [PATCH] btrfs: don't fallback to buffered IO for NOWAIT direct IO writes Currently, for a direct IO write, if we need to fallback to buffered IO, either to satisfy the whole write operation or just a part of it, we do it in the current context even if it's a NOWAIT context. This is not ideal because we currently don't have support for NOWAIT semantics in the buffered IO path (we can block for several reasons), so we should instead return -EAGAIN to the caller, so that it knows it should retry (the whole operation or what's left of it) in a context where blocking is acceptable. Signed-off-by: Filipe Manana Reviewed-by: David Sterba Signed-off-by: David Sterba --- fs/btrfs/file.c | 16 +++++++++++++++- 1 file changed, 15 insertions(+), 1 deletion(-) diff --git a/fs/btrfs/file.c b/fs/btrfs/file.c index f406a662e942..687fb372093f 100644 --- a/fs/btrfs/file.c +++ b/fs/btrfs/file.c @@ -1971,11 +1971,25 @@ again: if (is_sync_write) iocb->ki_flags |= IOCB_DSYNC; - /* If 'err' is -ENOTBLK then it means we must fallback to buffered IO. */ + /* + * If 'err' is -ENOTBLK or we have not written all data, then it means + * we must fallback to buffered IO. + */ if ((err < 0 && err != -ENOTBLK) || !iov_iter_count(from)) goto out; buffered: + /* + * If we are in a NOWAIT context, then return -EAGAIN to signal the caller + * it must retry the operation in a context where blocking is acceptable, + * since we currently don't have NOWAIT semantics support for buffered IO + * and may block there for many reasons (reserving space for example). + */ + if (iocb->ki_flags & IOCB_NOWAIT) { + err = -EAGAIN; + goto out; + } + pos = iocb->ki_pos; written_buffered = btrfs_buffered_write(iocb, from); if (written_buffered < 0) { -- 2.20.1