linux-kernel - Re: [PATCH v4] ceph: invalidate pages when doing direct/sync writes

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Date:   Fri, 8 Apr 2022 03:03:10 +0800
From:   Xiubo Li <xiubli@...hat.com>
To:     Luís Henriques <lhenriques@...e.de>,
        Jeff Layton <jlayton@...nel.org>,
        Ilya Dryomov <idryomov@...il.com>
Cc:     ceph-devel@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4] ceph: invalidate pages when doing direct/sync writes


On 4/7/22 11:15 PM, Luís Henriques wrote:
> When doing a direct/sync write, we need to invalidate the page cache in
> the range being written to.  If we don't do this, the cache will include
> invalid data as we just did a write that avoided the page cache.
>
> Signed-off-by: Luís Henriques <lhenriques@...e.de>
> ---
>   fs/ceph/file.c | 19 ++++++++++++++-----
>   1 file changed, 14 insertions(+), 5 deletions(-)
>
> Changes since v3:
> - Dropped initial call to invalidate_inode_pages2_range()
> - Added extra comment to document invalidation
>
> Changes since v2:
> - Invalidation needs to be done after a write
>
> Changes since v1:
> - Replaced truncate_inode_pages_range() by invalidate_inode_pages2_range
> - Call fscache_invalidate with FSCACHE_INVAL_DIO_WRITE if we're doing DIO
>
> diff --git a/fs/ceph/file.c b/fs/ceph/file.c
> index 5072570c2203..97f764b2fbdd 100644
> --- a/fs/ceph/file.c
> +++ b/fs/ceph/file.c
> @@ -1606,11 +1606,6 @@ ceph_sync_write(struct kiocb *iocb, struct iov_iter *from, loff_t pos,
>   		return ret;
>   
>   	ceph_fscache_invalidate(inode, false);
> -	ret = invalidate_inode_pages2_range(inode->i_mapping,
> -					    pos >> PAGE_SHIFT,
> -					    (pos + count - 1) >> PAGE_SHIFT);
> -	if (ret < 0)
> -		dout("invalidate_inode_pages2_range returned %d\n", ret);
>   
>   	while ((len = iov_iter_count(from)) > 0) {
>   		size_t left;
> @@ -1938,6 +1933,20 @@ ceph_sync_write(struct kiocb *iocb, struct iov_iter *from, loff_t pos,
>   			break;
>   		}
>   		ceph_clear_error_write(ci);
> +
> +		/*
> +		 * we need to invalidate the page cache here, otherwise the
> +		 * cache will include invalid data in direct/sync writes.
> +		 */
> +		ret = invalidate_inode_pages2_range(

IMO we'd better use truncate_inode_pages_range() after write. The above 
means it's possibly will write the dirty pagecache back, which will 
overwrite and corrupt the disk data just wrote.

Though it seems impossible that these pagecaches will be marked dirty, 
but this call is misleading ?

-- Xiubo

> +				inode->i_mapping,
> +				pos >> PAGE_SHIFT,
> +				(pos + len - 1) >> PAGE_SHIFT);
> +		if (ret < 0) {
> +			dout("invalidate_inode_pages2_range returned %d\n",
> +			     ret);
> +			ret = 0;
> +		}
>   		pos += len;
>   		written += len;
>   		dout("sync_write written %d\n", written);
>