linux-ext4 - Re: [PATCH 7/8] nowait aio: xfs

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Date:   Mon, 3 Apr 2017 23:52:11 -0700
From:   Christoph Hellwig <hch@...radead.org>
To:     Goldwyn Rodrigues <rgoldwyn@...e.de>
Cc:     linux-fsdevel@...r.kernel.org, jack@...e.com, hch@...radead.org,
        linux-block@...r.kernel.org, linux-btrfs@...r.kernel.org,
        linux-ext4@...r.kernel.org, linux-xfs@...r.kernel.org,
        sagi@...mberg.me, avi@...lladb.com, axboe@...nel.dk,
        linux-api@...r.kernel.org, willy@...radead.org,
        tom.leiming@...il.com, Goldwyn Rodrigues <rgoldwyn@...e.com>
Subject: Re: [PATCH 7/8] nowait aio: xfs

> +	if (unaligned_io) {
> +		/* If we are going to wait for other DIO to finish, bail */
> +		if ((iocb->ki_flags & IOCB_NOWAIT) &&
> +		     atomic_read(&inode->i_dio_count))
> +			return -EAGAIN;
>  		inode_dio_wait(inode);

This checks i_dio_count twice in the nowait case, I think it should be:

	if (iocb->ki_flags & IOCB_NOWAIT) {
		if (atomic_read(&inode->i_dio_count))
			return -EAGAIN;
	} else {
		inode_dio_wait(inode);
	}

>  	if ((flags & (IOMAP_WRITE | IOMAP_ZERO)) && xfs_is_reflink_inode(ip)) {
>  		if (flags & IOMAP_DIRECT) {
> +			/* A reflinked inode will result in CoW alloc */
> +			if (flags & IOMAP_NOWAIT) {
> +				error = -EAGAIN;
> +				goto out_unlock;
> +			}

This is a bit pessimistic - just because the inode has any shared
extents we could still write into unshared ones.  For now I think this
pessimistic check is fine, but the comment should be corrected.