linux-kernel - Re: [PATCH 13/20] fuse, dax: Implement dax read/write operations

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Date:   Tue, 14 Apr 2020 08:54:11 -0400
From:   Vivek Goyal <vgoyal@...hat.com>
To:     Liu Bo <bo.liu@...ux.alibaba.com>
Cc:     linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-nvdimm@...ts.01.org, virtio-fs@...hat.com, miklos@...redi.hu,
        stefanha@...hat.com, dgilbert@...hat.com, mst@...hat.com,
        Miklos Szeredi <mszeredi@...hat.com>,
        Peng Tao <tao.peng@...ux.alibaba.com>
Subject: Re: [PATCH 13/20] fuse, dax: Implement dax read/write operations

On Sat, Apr 04, 2020 at 08:25:21AM +0800, Liu Bo wrote:

[..]
> > +static int iomap_begin_upgrade_mapping(struct inode *inode, loff_t pos,
> > +					 loff_t length, unsigned flags,
> > +					 struct iomap *iomap)
> > +{
> > +	struct fuse_inode *fi = get_fuse_inode(inode);
> > +	struct fuse_dax_mapping *dmap;
> > +	int ret;
> > +
> > +	/*
> > +	 * Take exclusive lock so that only one caller can try to setup
> > +	 * mapping and others wait.
> > +	 */
> > +	down_write(&fi->i_dmap_sem);
> > +	dmap = fuse_dax_interval_tree_iter_first(&fi->dmap_tree, pos, pos);
> > +
> > +	/* We are holding either inode lock or i_mmap_sem, and that should
> > +	 * ensure that dmap can't reclaimed or truncated and it should still
> > +	 * be there in tree despite the fact we dropped and re-acquired the
> > +	 * lock.
> > +	 */
> > +	ret = -EIO;
> > +	if (WARN_ON(!dmap))
> > +		goto out_err;
> > +
> > +	/* Maybe another thread already upgraded mapping while we were not
> > +	 * holding lock.
> > +	 */
> > +	if (dmap->writable)
> 
> oops, looks like it's still returning -EIO here, %ret should be zero.
> 

Good catch. Will fix it.

Vivek