On Wed, 2018-03-28 at 12:18 -0400, Trond Myklebust wrote:
> Currently the knfsd replay cache appears to try to refuse replying to
> retries that come within 200ms of the cache entry being created. That
> makes limited sense in today's world of high speed TCP.
>
> Signed-off-by: Trond Myklebust <trond.myklebust@xxxxxxxxxxxxxxx>
> ---
> fs/nfsd/cache.h | 5 -----
> fs/nfsd/nfscache.c | 6 ++----
> 2 files changed, 2 insertions(+), 9 deletions(-)
>
> diff --git a/fs/nfsd/cache.h b/fs/nfsd/cache.h
> index 046b3f048757..b7559c6f2b97 100644
> --- a/fs/nfsd/cache.h
> +++ b/fs/nfsd/cache.h
> @@ -67,11 +67,6 @@ enum {
> RC_REPLBUFF,
> };
>
> -/*
> - * If requests are retransmitted within this interval, they're
> dropped.
> - */
> -#define RC_DELAY (HZ/5)
> -
> /* Cache entries expire after this time period */
> #define RC_EXPIRE (120 * HZ)
>
> diff --git a/fs/nfsd/nfscache.c b/fs/nfsd/nfscache.c
> index 334f2ad60704..637f87c39183 100644
> --- a/fs/nfsd/nfscache.c
> +++ b/fs/nfsd/nfscache.c
> @@ -394,7 +394,6 @@ nfsd_cache_lookup(struct svc_rqst *rqstp)
> __wsum csum;
> u32 hash = nfsd_cache_hash(xid);
> struct nfsd_drc_bucket *b = &drc_hashtbl[hash];
> - unsigned long age;
> int type = rqstp->rq_cachetype;
> int rtn = RC_DOIT;
>
> @@ -461,12 +460,11 @@ nfsd_cache_lookup(struct svc_rqst *rqstp)
> found_entry:
> nfsdstats.rchits++;
> /* We found a matching entry which is either in progress or
> done. */
> - age = jiffies - rp->c_timestamp;
> lru_put_end(b, rp);
>
> rtn = RC_DROPIT;
> - /* Request being processed or excessive rexmits */
> - if (rp->c_state == RC_INPROG || age < RC_DELAY)
> + /* Request being processed */
> + if (rp->c_state == RC_INPROG)
> goto out;
>
> /* From the hall of fame of impractical attacks:
That condition always looked a bit suspicious to me.
Acked-by: Jeff Layton <jlayton@xxxxxxxxxx>
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