[dm-devel] [PATCH 8/8] multipathd: handle repeated udev retrigger failure

[Benjamin Marzinski]

On Wed, Oct 10, 2018 at 10:05:06PM +0200, Martin Wilck wrote:
> If a path was still not properly initialized after exhausting the
> retrigger tries, it used to remain in INIT_MISSING_UDEV state forever.
> get_uid() might fall back to non-udev-based methods to determine
> the WWID, but it would never be called for a path in this state any more.
> 
> This patch changes this behavior by resetting the path back to FAILED
> state if udev can't provide the WWID even after retriggering. Now, if
> the path ever happens to be in PATH_UP or PATH_GHOST state again,
> pathinfo(DI_ALL) will be called from check_path(), and there's at least
> some chance to obtain a WWID for it.

What you have seems reasonable, but looking at the code that calls
pathinfo() in this case, I do have some related suggestions.

Since check_path() always returns early if !pp->mpp and
pp->initialized != INIT_FAILED, we don't need the
pp->initialized != INIT_MISSING_UDEV check before doing the pathinfo
(although we might want to check pp->initialized == INIT_FAILED, in case
we add other pp->initialized states in the future).

Also, I don't think that checking if pathinfo returns PATHINFO_OK is the
right thing to do before calling ev_add_path(). pathinfo() will return
PATHINFO_OK even if we fail to get the wwid. I'm pretty sure this should
check if pp->initialized == INIT_OK instead.

Finally, if pp->initialized != INIT_OK after the call to pathinfo(),
would you object to setting pp->tick to max_checkint so that we don't
keep checking the path as often.  It is possible that this really is a
device that shouldn't be multipathed, and for which we will never be
able to get a wwid. It seems like after some many failures, we don't
need to be so proactive about rechecking an active path where we simply
aren't getting the wwid.

-Ben

> 
> Signed-off-by: Martin Wilck <mwilck at suse.com>
> ---
>  multipathd/main.c | 32 +++++++++++++++++++++++---------
>  1 file changed, 23 insertions(+), 9 deletions(-)
> 
> diff --git a/multipathd/main.c b/multipathd/main.c
> index 2d45d989..a9e1a4bd 100644
> --- a/multipathd/main.c
> +++ b/multipathd/main.c
> @@ -1828,15 +1828,29 @@ check_path (struct vectors * vecs, struct path * pp, int ticks)
>  	retrigger_tries = conf->retrigger_tries;
>  	checkint = conf->checkint;
>  	put_multipath_config(conf);
> -	if (!pp->mpp && pp->initialized == INIT_MISSING_UDEV &&
> -	    pp->retriggers < retrigger_tries) {
> -		condlog(2, "%s: triggering change event to reinitialize",
> -			pp->dev);
> -		pp->initialized = INIT_REQUESTED_UDEV;
> -		pp->retriggers++;
> -		sysfs_attr_set_value(pp->udev, "uevent", "change",
> -				     strlen("change"));
> -		return 0;
> +	if (!pp->mpp && pp->initialized == INIT_MISSING_UDEV) {
> +		if (pp->retriggers < retrigger_tries) {
> +			condlog(2, "%s: triggering change event to reinitialize",
> +				pp->dev);
> +			pp->initialized = INIT_REQUESTED_UDEV;
> +			pp->retriggers++;
> +			sysfs_attr_set_value(pp->udev, "uevent", "change",
> +					     strlen("change"));
> +			return 0;
> +		} else {
> +			condlog(1, "%s: not initialized after %d udev retriggers",
> +				pp->dev, retrigger_tries);
> +			/*
> +			 * Make sure that the "add missing path" code path
> +			 * below may reinstate the path later, if it ever
> +			 * comes up again.
> +			 * The WWID needs not be cleared; if it was set, the
> +			 * state hadn't been INIT_MISSING_UDEV in the first
> +			 * place.
> +			 */
> +			pp->initialized = INIT_FAILED;
> +			return 0;
> +		}
>  	}
>  
>  	/*
> -- 
> 2.19.0