Return-Path: linux-nfs-owner@vger.kernel.org Received: from fieldses.org ([174.143.236.118]:38636 "EHLO fieldses.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754185Ab3BDPyV (ORCPT ); Mon, 4 Feb 2013 10:54:21 -0500 Date: Mon, 4 Feb 2013 10:54:20 -0500 From: "J. Bruce Fields" To: Jeff Layton Cc: linux-nfs@vger.kernel.org Subject: Re: [PATCH v2 8/8] nfsd: keep a checksum of the first 256 bytes of request Message-ID: <20130204155420.GB815@fieldses.org> References: <1359983887-28535-1-git-send-email-jlayton@redhat.com> <1359983887-28535-9-git-send-email-jlayton@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii In-Reply-To: <1359983887-28535-9-git-send-email-jlayton@redhat.com> Sender: linux-nfs-owner@vger.kernel.org List-ID: On Mon, Feb 04, 2013 at 08:18:07AM -0500, Jeff Layton wrote: > Now that we're allowing more DRC entries, it becomes a lot easier to hit > problems with XID collisions. In order to mitigate those, calculate the > crc32 of up to the first 256 bytes of each request coming in and store > that in the cache entry, along with the total length of the request. > > Signed-off-by: Jeff Layton > --- > fs/nfsd/cache.h | 5 +++++ > fs/nfsd/nfscache.c | 44 ++++++++++++++++++++++++++++++++++++++++---- > 2 files changed, 45 insertions(+), 4 deletions(-) > > diff --git a/fs/nfsd/cache.h b/fs/nfsd/cache.h > index 9c7232b..4822db3 100644 > --- a/fs/nfsd/cache.h > +++ b/fs/nfsd/cache.h > @@ -29,6 +29,8 @@ struct svc_cacherep { > u32 c_prot; > u32 c_proc; > u32 c_vers; > + unsigned int c_len; > + u32 c_crc; > unsigned long c_timestamp; > union { > struct kvec u_vec; > @@ -73,6 +75,9 @@ enum { > /* Cache entries expire after this time period */ > #define RC_EXPIRE (120 * HZ) > > +/* Checksum this amount of the request */ > +#define RC_CSUMLEN (256U) > + > int nfsd_reply_cache_init(void); > void nfsd_reply_cache_shutdown(void); > int nfsd_cache_lookup(struct svc_rqst *); > diff --git a/fs/nfsd/nfscache.c b/fs/nfsd/nfscache.c > index d16a5d6..cb655f3 100644 > --- a/fs/nfsd/nfscache.c > +++ b/fs/nfsd/nfscache.c > @@ -11,6 +11,7 @@ > #include > #include > #include > +#include > > #include "nfsd.h" > #include "cache.h" > @@ -24,6 +25,7 @@ static struct list_head lru_head; > static struct kmem_cache *drc_slab; > static unsigned int num_drc_entries; > static unsigned int max_drc_entries; > +static u32 crc_seed; > > /* > * Calculate the hash index from an XID. > @@ -130,6 +132,9 @@ int nfsd_reply_cache_init(void) > INIT_LIST_HEAD(&lru_head); > max_drc_entries = nfsd_cache_size_limit(); > num_drc_entries = 0; > + > + /* Is a random seed any better than some well-defined constant? */ > + get_random_bytes(&crc_seed, sizeof(crc_seed)); > return 0; > out_nomem: > printk(KERN_ERR "nfsd: failed to allocate reply cache\n"); > @@ -238,12 +243,37 @@ nfsd_reply_cache_shrink(struct shrinker *shrink, struct shrink_control *sc) > } > > /* > + * Walk an xdr_buf and get a CRC for at most the first RC_CSUMLEN bytes > + */ > +static u32 > +nfsd_cache_crc(struct xdr_buf *buf) > +{ > + u32 crc; > + const unsigned char *p = buf->head[0].iov_base; > + size_t csum_len = min_t(size_t, buf->head[0].iov_len + buf->page_len, > + RC_CSUMLEN); > + size_t len = min(buf->head[0].iov_len, csum_len); > + > + /* rq_arg.head first */ > + crc = crc32(crc_seed, p, len); > + csum_len -= len; > + > + /* Nothing left */ > + if (!csum_len) > + return crc; > + > + /* checksum the rest from the page_array */ > + p = page_address(buf->pages[0]) + buf->page_base; If buf->page_base is large (close to PAGE_SIZE), then reads past the end of the page when it should be continuing to the next page. In practice page_base is always 0 here, and I think it's unlikely that will change. But it would be worth a comment. (Or maybe even a WARN_ON_ONCE(buf->page_base).) > + return crc32(crc, p, csum_len); > +} > + > +/* > * Search the request hash for an entry that matches the given rqstp. > * Must be called with cache_lock held. Returns the found entry or > * NULL on failure. > */ > static struct svc_cacherep * > -nfsd_cache_search(struct svc_rqst *rqstp) > +nfsd_cache_search(struct svc_rqst *rqstp, u32 crc) > { > struct svc_cacherep *rp; > struct hlist_node *hn; > @@ -257,6 +287,7 @@ nfsd_cache_search(struct svc_rqst *rqstp) > hlist_for_each_entry(rp, hn, rh, c_hash) { > if (xid == rp->c_xid && proc == rp->c_proc && > proto == rp->c_prot && vers == rp->c_vers && > + rqstp->rq_arg.len == rp->c_len && crc == rp->c_crc && > rpc_cmp_addr(svc_addr(rqstp), (struct sockaddr *)&rp->c_addr) && > rpc_get_port(svc_addr(rqstp)) == rpc_get_port((struct sockaddr *)&rp->c_addr)) > return rp; > @@ -276,7 +307,8 @@ nfsd_cache_lookup(struct svc_rqst *rqstp) > __be32 xid = rqstp->rq_xid; > u32 proto = rqstp->rq_prot, > vers = rqstp->rq_vers, > - proc = rqstp->rq_proc; > + proc = rqstp->rq_proc, > + crc; > unsigned long age; > int type = rqstp->rq_cachetype; > int rtn; > @@ -287,10 +319,12 @@ nfsd_cache_lookup(struct svc_rqst *rqstp) > return RC_DOIT; > } > > + crc = nfsd_cache_crc(&rqstp->rq_arg); > + For a moment I was wondering whether we should delay calculating that till we need it--but of course we need it in all cases but allocation failure (either to match an existing entry or populate a new one). OK! Looks fine.--b. > spin_lock(&cache_lock); > rtn = RC_DOIT; > > - rp = nfsd_cache_search(rqstp); > + rp = nfsd_cache_search(rqstp, crc); > if (rp) > goto found_entry; > > @@ -318,7 +352,7 @@ nfsd_cache_lookup(struct svc_rqst *rqstp) > * Must search again just in case someone inserted one > * after we dropped the lock above. > */ > - found = nfsd_cache_search(rqstp); > + found = nfsd_cache_search(rqstp, crc); > if (found) { > nfsd_reply_cache_free_locked(rp); > rp = found; > @@ -344,6 +378,8 @@ setup_entry: > rpc_set_port((struct sockaddr *)&rp->c_addr, rpc_get_port(svc_addr(rqstp))); > rp->c_prot = proto; > rp->c_vers = vers; > + rp->c_len = rqstp->rq_arg.len; > + rp->c_crc = crc; > > hash_refile(rp); > lru_put_end(rp); > -- > 1.7.11.7 >