linux-ext4 - Re: [PATCH 2/2] ext4: handle layout changes to pinned DAX mappings

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Message-ID: <20180622082533.biejwdtrn4tymiy4@quack2.suse.cz>
Date:   Fri, 22 Jun 2018 10:25:33 +0200
From:   Jan Kara <jack@...e.cz>
To:     Ross Zwisler <ross.zwisler@...ux.intel.com>
Cc:     Jan Kara <jack@...e.cz>, Dan Williams <dan.j.williams@...el.com>,
        Dave Chinner <david@...morbit.com>,
        Christoph Hellwig <hch@....de>, linux-nvdimm@...ts.01.org,
        Jeff Moyer <jmoyer@...hat.com>, linux-ext4@...r.kernel.org
Subject: Re: [PATCH 2/2] ext4: handle layout changes to pinned DAX mappings

On Wed 20-06-18 16:15:03, Ross Zwisler wrote:
> diff --git a/fs/ext4/truncate.h b/fs/ext4/truncate.h
> index 0cb13badf473..a3b78241e9f6 100644
> --- a/fs/ext4/truncate.h
> +++ b/fs/ext4/truncate.h
> @@ -12,6 +12,7 @@
>  static inline void ext4_truncate_failed_write(struct inode *inode)
>  {
>  	down_write(&EXT4_I(inode)->i_mmap_sem);
> +	ext4_break_layouts(inode);
>  	truncate_inode_pages(inode->i_mapping, inode->i_size);
>  	ext4_truncate(inode);
>  	up_write(&EXT4_I(inode)->i_mmap_sem);

One comment here: I don't think ext4_break_layouts() is necessary here.
ext4_truncate_failed_write() exists to truncate blocks beyond EOF. As such
these blocks could never be even mmaped, let alone pinned by GUP. Maybe
just add a comment that blocks we are truncating here were never visible to
userspace and so we don't need ext4_break_layouts() protection.

								Honza
-- 
Jan Kara <jack@...e.com>
SUSE Labs, CR