[lustre-devel] [PATCH/RFC] lustre: changelog_cdev need to find obd on each access.

[quentin.bouget at cea.fr]

Le 07/11/2018 à 02:09, NeilBrown a écrit :
> A changelog cdev can be held open indefinitely, and obd structures can
> come and go while it is open.  So it isn't safe to choose and obd
> at open time, and continue to use it.
>
> Instead, we need to choose and obd on each access that needs it, and
> hold the chlg_registered_dev_lock mutex while using the obd.  This
> prevents the obd from being freed.
`struct llog_ctxt' has a reference on that obd (and `struct llog_handle' 
has a reference on a `struct llog_ctxt').
I don't think letting the obd go away is safe.

> @@ -193,11 +204,17 @@ static void enq_record_delete(struct chlg_rec_entry *rec)
>   static int chlg_load(void *args)
>   {
>   	struct chlg_reader_state *crs = args;
> -	struct obd_device *obd = crs->crs_obd;
> +	struct obd_device *obd;
>   	struct llog_ctxt *ctx = NULL;
>   	struct llog_handle *llh = NULL;
>   	int rc;
>   
> +	mutex_lock(&chlg_registered_dev_lock);
> +	obd = chlg_obd_get(crs->crs_dev);
> +	if (!obd) {
> +		rc = -ENOENT;
> +		goto err_out;
> +	}
>   	ctx = llog_get_context(obd, LLOG_CHANGELOG_REPL_CTXT);
 From there the obd is irrevocably referenced. I suspect it is used for 
more than just its name.
Maybe trying to unmount the (wrong) mountpoint will fail after that, but 
I am not confident.

Quentin