From: Filipe Manana Date: Mon, 4 Jul 2022 11:42:04 +0000 (+0100) Subject: btrfs: don't fallback to buffered IO for NOWAIT direct IO writes X-Git-Url: http://git.maquefel.me/?a=commitdiff_plain;h=ac5e666951507ceb1da2ed85c4f5c7bb88bec06e;p=linux.git 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 --- diff --git a/fs/btrfs/file.c b/fs/btrfs/file.c index f406a662e9429..687fb372093fa 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) {