Re: [PATCH 7/9] smb: client: block cache=ro and cache=singleclient on remount

Meetakshi Setiya
2026-04-13T13:40:59Z

Hey Rajasi,

I guess this is not handling remounts where cache=singleclient/ro is
not specified i.e. preserving previous behaviour.

To reproduce, mount with cache=ro and remount without providing cache=ro.

sudo mount -t cifs //server/winshare /mnt/mainshare -o
remount,username=demouser
mount error(22): Invalid argument

On Thu, Apr 9, 2026 at 3:07 AM <rajasimandalos@gmail.com> wrote:
>
> From: Rajasi Mandal <rajasimandal@microsoft.com>
>
> cache=ro and cache=singleclient are mount-time environment declarations
> where the admin promises that the share is read-only or exclusively
> accessed. The client bypasses server-based coherency (oplocks/leases)
> and caches aggressively based on this promise.
>
> These modes were intentionally excluded from smb3_update_mnt_flags()
> when it was introduced in commit 2d39f50c2b15 ("cifs: move update of
> flags into a separate function") — only cache=strict, cache=none and
> cache=loose were made reconfigurable. However, remount currently
> silently accepts cache=ro and cache=singleclient without actually
> applying them, which is confusing.
>
> Add explicit checks in smb3_verify_reconfigure_ctx() to reject
> attempts to change these options during remount with a clear error
> message.
>
> Signed-off-by: Rajasi Mandal <rajasimandal@microsoft.com>
> ---
> fs/smb/client/fs_context.c | 8 ++++++++
> 1 file changed, 8 insertions(+)
>
> diff --git a/fs/smb/client/fs_context.c b/fs/smb/client/fs_context.c
> index ce4842e778c4..2be72733ef2e 100644
> --- a/fs/smb/client/fs_context.c
> +++ b/fs/smb/client/fs_context.c
> @@ -1180,6 +1180,14 @@ static int smb3_verify_reconfigure_ctx(struct fs_context *fc,
> cifs_errorf(fc, "can not change rdma during remount\n");
> return -EINVAL;
> }
> + if (new_ctx->cache_ro != old_ctx->cache_ro) {
> + cifs_errorf(fc, "can not change cache=ro during remount\n");
> + return -EINVAL;
> + }
> + if (new_ctx->cache_rw != old_ctx->cache_rw) {
> + cifs_errorf(fc, "can not change cache=singleclient during remount\n");
> + return -EINVAL;
> + }
>
> return 0;
> }
> --
> 2.43.0
>
>