Re: [PATCH] cifs: destage dirty pages before re-reading them for cache=none

[Tom Talpey <tom@talpey.com>]

On 9/19/2022 5:37 PM, Ronnie Sahlberg wrote:
> This is the opposite case of kernel bugzilla 216301.
> If we mmap a file using cache=none and then proceed to update the mmapped
> area these updates are not reflected in a later pread() of that part of the
> file.
> To fix this we must first destage any dirty pages in the range before
> we allow the pread() to proceed.
> 
> Reviewed-by: Paulo Alcantara (SUSE) <pc@cjr.nz>
> Reviewed-by: Enzo Matsumiya <ematsumiya@suse.de>
> Signed-off-by: Ronnie Sahlberg <lsahlber@redhat.com>
> ---
>   fs/cifs/file.c | 9 +++++++++
>   1 file changed, 9 insertions(+)
> 
> diff --git a/fs/cifs/file.c b/fs/cifs/file.c
> index 6f38b134a346..1f3eb97ef4ab 100644
> --- a/fs/cifs/file.c
> +++ b/fs/cifs/file.c
> @@ -4271,6 +4271,15 @@ static ssize_t __cifs_readv(
>   		len = ctx->len;
>   	}
>   
> +	if (direct) {
> +		rc = filemap_write_and_wait_range(file->f_inode->i_mapping,
> +						  offset, offset + len - 1);
> +		if (rc) {
> +			kref_put(&ctx->refcount, cifs_aio_ctx_release);
> +			return rc;

Are the possible return values from filemap_write_and_wait_range() also
valid for returning from __cifs_readv()? It seems a bit odd to return
write errors here.

If not, then perhaps a more generic failure rc would be safer/more POSIX
compliant?

Tom.

> +		}
> +	}
> +
>   	/* grab a lock here due to read response handlers can access ctx */
>   	mutex_lock(&ctx->aio_mutex);
>