2021-12-17 20:23 GMT+09:00, Vasily Averin <vvs@xxxxxxxxxxxxx>:
> Like nfsd and lockd, ksmbd can cause deadlock if the exported
> file system does not support asynchronous processing of blocking locks:
> if all ksmbd worker threads handles such requests,
> they can never finish and the server will not be able to handle
> any other incoming requests.
>
> Any filesystem that leaves ->lock NULL will use posix_lock_file(), which
> does the right thing. Simplest is just to assume that any filesystem
> that defines its own ->lock is not safe to request a blocking lock from.
>
> To work around the problem we need to drop fl->fl_flag FL_SLEEP before
> vfs_lock_file() execution, it forces affected functions to avoid blocking.
>
> Signed-off-by: Vasily Averin <vvs@xxxxxxxxxxxxx>
Acked-by: Namjae Jeon <linkinjeon@xxxxxxxxxx>
Thanks!
> ---
> fs/ksmbd/smb2pdu.c | 6 ++++++
> 1 file changed, 6 insertions(+)
>
> diff --git a/fs/ksmbd/smb2pdu.c b/fs/ksmbd/smb2pdu.c
> index 121f8e8c70ac..f2225491af02 100644
> --- a/fs/ksmbd/smb2pdu.c
> +++ b/fs/ksmbd/smb2pdu.c
> @@ -6634,6 +6634,12 @@ static int smb2_set_flock_flags(struct file_lock
> *flock, int flags)
> {
> int cmd = -EINVAL;
>
> + if ((flock->fl_file->f_op->lock) &&
> + ((flags == SMB2_LOCKFLAG_SHARED) ||
> + (flags == SMB2_LOCKFLAG_EXCLUSIVE))) {
> + ksmbd_debug(SMB, "force fail immediately request\n");
> + flags |= SMB2_LOCKFLAG_FAIL_IMMEDIATELY;
> + }
> /* Checking for wrong flag combination during lock request*/
> switch (flags) {
> case SMB2_LOCKFLAG_SHARED:
> --
> 2.25.1
>
>
