linux-kernel - Re: [PATCH] ceph: truncate page cache when doing DIO in encrypted inodes

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Message-ID: <0f781fa1b2bec48d40729d8306a2ed8b19209734.camel@kernel.org>
Date:   Fri, 01 Apr 2022 07:56:23 -0400
From:   Jeff Layton <jlayton@...nel.org>
To:     Luís Henriques <lhenriques@...e.de>,
        Xiubo Li <xiubli@...hat.com>, Ilya Dryomov <idryomov@...il.com>
Cc:     ceph-devel@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] ceph: truncate page cache when doing DIO in encrypted
 inodes

On Fri, 2022-04-01 at 12:38 +0100, Luís Henriques wrote:
> When doing DIO on an encrypted node, we need to truncate the page cache in
> the range being written to, otherwise the cache will include invalid data.
> 
> Signed-off-by: Luís Henriques <lhenriques@...e.de>
> ---
>  fs/ceph/file.c | 5 +++++
>  1 file changed, 5 insertions(+)
> 
> This patch should fix generic/647 fstest when run with test_dummy_encryption.
> 
> diff --git a/fs/ceph/file.c b/fs/ceph/file.c
> index 5072570c2203..0f31c4d352a4 100644
> --- a/fs/ceph/file.c
> +++ b/fs/ceph/file.c
> @@ -1895,6 +1895,11 @@ ceph_sync_write(struct kiocb *iocb, struct iov_iter *from, loff_t pos,
>  		req->r_inode = inode;
>  		req->r_mtime = mtime;
>  
> +		if (IS_ENCRYPTED(inode) && (iocb->ki_flags & IOCB_DIRECT))
> +			truncate_inode_pages_range(
> +				inode->i_mapping, write_pos,
> +				PAGE_ALIGN(write_pos + write_len) - 1);
> +
>  		/* Set up the assertion */
>  		if (rmw) {
>  			/*

Truncating the pagecache like this could cause dirty data to be
discarded. I know we're planning to overwrite this range, but you are
having to invalidate more than the written range here. We could
potentially lose a write to that region.

Have you tried using something like invalidate_inode_pages2_range ?
That's more of what we'd want here, as it's a bit more cautious about
tossing out dirty pages. I see too that that is what
ceph_direct_read_write calls in the write case as well.
-- 
Jeff Layton <jlayton@...nel.org>