linux-kernel - Re: [PATCH v2 2/8] fsdax: invalidate pages when CoW

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Date:   Thu, 1 Dec 2022 08:17:14 -0800
From:   "Darrick J. Wong" <djwong@...nel.org>
To:     Shiyang Ruan <ruansy.fnst@...itsu.com>
Cc:     linux-kernel@...r.kernel.org, linux-xfs@...r.kernel.org,
        nvdimm@...ts.linux.dev, linux-fsdevel@...r.kernel.org,
        david@...morbit.com, dan.j.williams@...el.com,
        akpm@...ux-foundation.org
Subject: Re: [PATCH v2 2/8] fsdax: invalidate pages when CoW

On Thu, Dec 01, 2022 at 03:28:52PM +0000, Shiyang Ruan wrote:
> CoW changes the share state of a dax page, but the share count of the
> page isn't updated.  The next time access this page, it should have been
> a newly accessed, but old association exists.  So, we need to clear the
> share state when CoW happens, in both dax_iomap_rw() and
> dax_zero_iter().
> 
> Signed-off-by: Shiyang Ruan <ruansy.fnst@...itsu.com>

Looks ok,
Reviewed-by: Darrick J. Wong <djwong@...nel.org>

--D

> ---
>  fs/dax.c | 17 +++++++++++++----
>  1 file changed, 13 insertions(+), 4 deletions(-)
> 
> diff --git a/fs/dax.c b/fs/dax.c
> index 85b81963ea31..482dda85ccaf 100644
> --- a/fs/dax.c
> +++ b/fs/dax.c
> @@ -1264,6 +1264,15 @@ static s64 dax_zero_iter(struct iomap_iter *iter, bool *did_zero)
>  	if (srcmap->type == IOMAP_HOLE || srcmap->type == IOMAP_UNWRITTEN)
>  		return length;
>  
> +	/*
> +	 * invalidate the pages whose sharing state is to be changed
> +	 * because of CoW.
> +	 */
> +	if (iomap->flags & IOMAP_F_SHARED)
> +		invalidate_inode_pages2_range(iter->inode->i_mapping,
> +					      pos >> PAGE_SHIFT,
> +					      (pos + length - 1) >> PAGE_SHIFT);
> +
>  	do {
>  		unsigned offset = offset_in_page(pos);
>  		unsigned size = min_t(u64, PAGE_SIZE - offset, length);
> @@ -1324,12 +1333,13 @@ static loff_t dax_iomap_iter(const struct iomap_iter *iomi,
>  		struct iov_iter *iter)
>  {
>  	const struct iomap *iomap = &iomi->iomap;
> -	const struct iomap *srcmap = &iomi->srcmap;
> +	const struct iomap *srcmap = iomap_iter_srcmap(iomi);
>  	loff_t length = iomap_length(iomi);
>  	loff_t pos = iomi->pos;
>  	struct dax_device *dax_dev = iomap->dax_dev;
>  	loff_t end = pos + length, done = 0;
>  	bool write = iov_iter_rw(iter) == WRITE;
> +	bool cow = write && iomap->flags & IOMAP_F_SHARED;
>  	ssize_t ret = 0;
>  	size_t xfer;
>  	int id;
> @@ -1356,7 +1366,7 @@ static loff_t dax_iomap_iter(const struct iomap_iter *iomi,
>  	 * into page tables. We have to tear down these mappings so that data
>  	 * written by write(2) is visible in mmap.
>  	 */
> -	if (iomap->flags & IOMAP_F_NEW) {
> +	if (iomap->flags & IOMAP_F_NEW || cow) {
>  		invalidate_inode_pages2_range(iomi->inode->i_mapping,
>  					      pos >> PAGE_SHIFT,
>  					      (end - 1) >> PAGE_SHIFT);
> @@ -1390,8 +1400,7 @@ static loff_t dax_iomap_iter(const struct iomap_iter *iomi,
>  			break;
>  		}
>  
> -		if (write &&
> -		    srcmap->type != IOMAP_HOLE && srcmap->addr != iomap->addr) {
> +		if (cow) {
>  			ret = dax_iomap_cow_copy(pos, length, PAGE_SIZE, srcmap,
>  						 kaddr);
>  			if (ret)
> -- 
> 2.38.1
>