Re: [PATCH 04/12] sunrpc/cache: recheck cache validity after cache_defer_req

J. Bruce Fields
2009-08-04T20:42:51Z

On Tue, Aug 04, 2009 at 03:22:38PM +1000, NeilBrown wrote:
> If cache_defer_req did not leave the request on a queue, then it could
> possibly have waited long enough that the cache became valid. So check the
> status after the call.
>
> Signed-off-by: NeilBrown <neilb@suse.de>
> ---
>
> net/sunrpc/cache.c | 53 ++++++++++++++++++++++++++++++++--------------------
> 1 files changed, 33 insertions(+), 20 deletions(-)
>
> diff --git a/net/sunrpc/cache.c b/net/sunrpc/cache.c
> index c1f897c..bff4baa 100644
> --- a/net/sunrpc/cache.c
> +++ b/net/sunrpc/cache.c
> @@ -173,6 +173,22 @@ struct cache_head *sunrpc_cache_update(struct cache_detail *detail,
> EXPORT_SYMBOL_GPL(sunrpc_cache_update);
>
> static int cache_make_upcall(struct cache_detail *detail, struct cache_head *h);
> +
> +static inline int cache_is_valid(struct cache_detail *detail, struct cache_head *h)
> +{
> + if (!test_bit(CACHE_VALID, &h->flags) ||
> + h->expiry_time < get_seconds())
> + return -EAGAIN;
> + else if (detail->flush_time > h->last_refresh)
> + return -EAGAIN;
> + else {
> + /* entry is valid */
> + if (test_bit(CACHE_NEGATIVE, &h->flags))
> + return -ENOENT;
> + else
> + return 0;
> + }
> +}
> /*
> * This is the generic cache management routine for all
> * the authentication caches.
> @@ -181,8 +197,10 @@ static int cache_make_upcall(struct cache_detail *detail, struct cache_head *h);
> *
> *
> * Returns 0 if the cache_head can be used, or cache_puts it and returns
> - * -EAGAIN if upcall is pending,
> - * -ETIMEDOUT if upcall failed and should be retried,
> + * -EAGAIN if upcall is pending and request has been queued
> + * -ETIMEDOUT if upcall failed or request could not be queue or

s/queue/queued/

> + * upcall completed but item is still invalid (implying that
> + * the cache item has been replaced with a newer one).
> * -ENOENT if cache entry was negative
> */
> int cache_check(struct cache_detail *detail,
> @@ -192,17 +210,7 @@ int cache_check(struct cache_detail *detail,
> long refresh_age, age;
>
> /* First decide return status as best we can */
> - if (!test_bit(CACHE_VALID, &h->flags) ||
> - h->expiry_time < get_seconds())
> - rv = -EAGAIN;
> - else if (detail->flush_time > h->last_refresh)
> - rv = -EAGAIN;
> - else {
> - /* entry is valid */
> - if (test_bit(CACHE_NEGATIVE, &h->flags))
> - rv = -ENOENT;
> - else rv = 0;
> - }
> + rv = cache_is_valid(detail, h);
>
> /* now see if we want to start an upcall */
> refresh_age = (h->expiry_time - h->last_refresh);
> @@ -235,10 +243,14 @@ int cache_check(struct cache_detail *detail,
> }
> }
>
> - if (rv == -EAGAIN)
> - if (cache_defer_req(rqstp, h) != 0)
> - rv = -ETIMEDOUT;
> -
> + if (rv == -EAGAIN) {
> + if (cache_defer_req(rqstp, h) == 0) {
> + /* Request is not deferred */

The code might be more self-explanatory if we wrote:

if (cache_defer_req(rqstp, h) == -ETIMEDOUT) {

Well, at least it would be obvious we're handling the "failure" case?
(Even if admittedly it's a "failure" that we may be able to handle).

It always takes me a little thought whenever I encounter a
boolean-returning function whose name doesn't have an obvious truth
value (list_empty, cache_is_valid).

No complaints otherwise.

--b.

> + rv = cache_is_valid(detail, h);
> + if (rv == -EAGAIN)
> + rv = -ETIMEDOUT;
> + }
> + }
> if (rv)
> cache_put(h, detail);
> return rv;
> @@ -557,11 +569,11 @@ static int cache_defer_req(struct cache_req *req, struct cache_head *item)
> * or continue and drop the oldest below
> */
> if (net_random()&1)
> - return -ETIMEDOUT;
> + return 0;
> }
> dreq = req->defer(req);
> if (dreq == NULL)
> - return -ETIMEDOUT;
> + return 0;
>
> dreq->item = item;
>
> @@ -591,8 +603,9 @@ static int cache_defer_req(struct cache_req *req, struct cache_head *item)
> if (!test_bit(CACHE_PENDING, &item->flags)) {
> /* must have just been validated... */
> cache_revisit_request(item);
> + return 0;
> }
> - return 0;
> + return 1;
> }
>
> static void cache_revisit_request(struct cache_head *item)
>
>