inet: frag: use seqlock for hash rebuild
rehash is rare operation, don't force readers to take
the read-side rwlock.
Instead, we only have to detect the (rare) case where
the secret was altered while we are trying to insert
a new inetfrag queue into the table.
If it was changed, drop the bucket lock and recompute
the hash to get the 'new' chain bucket that we have to
insert into.
Joint work with Nikolay Aleksandrov.
Signed-off-by: Florian Westphal <fw@strlen.de>
Signed-off-by: Nikolay Aleksandrov <nikolay@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/include/net/inet_frag.h b/include/net/inet_frag.h
index d9cc5bb..6f4930a 100644
--- a/include/net/inet_frag.h
+++ b/include/net/inet_frag.h
@@ -53,11 +53,6 @@
struct inet_frags {
struct inet_frag_bucket hash[INETFRAGS_HASHSZ];
- /* This rwlock is a global lock (seperate per IPv4, IPv6 and
- * netfilter). Important to keep this on a seperate cacheline.
- * Its primarily a rebuild protection rwlock.
- */
- rwlock_t lock ____cacheline_aligned_in_smp;
struct work_struct frags_work;
unsigned int next_bucket;
@@ -66,8 +61,12 @@
/* The first call to hashfn is responsible to initialize
* rnd. This is best done with net_get_random_once.
+ *
+ * rnd_seqlock is used to let hash insertion detect
+ * when it needs to re-lookup the hash chain to use.
*/
u32 rnd;
+ seqlock_t rnd_seqlock;
int qsize;
unsigned int (*hashfn)(const struct inet_frag_queue *);
@@ -89,8 +88,8 @@
void inet_frag_kill(struct inet_frag_queue *q, struct inet_frags *f);
void inet_frag_destroy(struct inet_frag_queue *q, struct inet_frags *f);
struct inet_frag_queue *inet_frag_find(struct netns_frags *nf,
- struct inet_frags *f, void *key, unsigned int hash)
- __releases(&f->lock);
+ struct inet_frags *f, void *key, unsigned int hash);
+
void inet_frag_maybe_warn_overflow(struct inet_frag_queue *q,
const char *prefix);
diff --git a/net/ieee802154/reassembly.c b/net/ieee802154/reassembly.c
index 20d2196..8da635d 100644
--- a/net/ieee802154/reassembly.c
+++ b/net/ieee802154/reassembly.c
@@ -124,7 +124,6 @@
arg.src = src;
arg.dst = dst;
- read_lock(&lowpan_frags.lock);
hash = lowpan_hash_frag(frag_info->d_tag, frag_info->d_size, src, dst);
q = inet_frag_find(&ieee802154_lowpan->frags,
diff --git a/net/ipv4/inet_fragment.c b/net/ipv4/inet_fragment.c
index 58d4c38..62b1f73 100644
--- a/net/ipv4/inet_fragment.c
+++ b/net/ipv4/inet_fragment.c
@@ -68,8 +68,7 @@
{
int i;
- /* Per bucket lock NOT needed here, due to write lock protection */
- write_lock_bh(&f->lock);
+ write_seqlock_bh(&f->rnd_seqlock);
if (!inet_frag_may_rebuild(f))
goto out;
@@ -82,6 +81,8 @@
struct hlist_node *n;
hb = &f->hash[i];
+ spin_lock(&hb->chain_lock);
+
hlist_for_each_entry_safe(q, n, &hb->chain, list) {
unsigned int hval = inet_frag_hashfn(f, q);
@@ -92,15 +93,28 @@
/* Relink to new hash chain. */
hb_dest = &f->hash[hval];
+
+ /* This is the only place where we take
+ * another chain_lock while already holding
+ * one. As this will not run concurrently,
+ * we cannot deadlock on hb_dest lock below, if its
+ * already locked it will be released soon since
+ * other caller cannot be waiting for hb lock
+ * that we've taken above.
+ */
+ spin_lock_nested(&hb_dest->chain_lock,
+ SINGLE_DEPTH_NESTING);
hlist_add_head(&q->list, &hb_dest->chain);
+ spin_unlock(&hb_dest->chain_lock);
}
}
+ spin_unlock(&hb->chain_lock);
}
f->rebuild = false;
f->last_rebuild_jiffies = jiffies;
out:
- write_unlock_bh(&f->lock);
+ write_sequnlock_bh(&f->rnd_seqlock);
}
static bool inet_fragq_should_evict(const struct inet_frag_queue *q)
@@ -163,7 +177,7 @@
BUILD_BUG_ON(INETFRAGS_EVICT_BUCKETS >= INETFRAGS_HASHSZ);
- read_lock_bh(&f->lock);
+ local_bh_disable();
for (i = ACCESS_ONCE(f->next_bucket); budget; --budget) {
evicted += inet_evict_bucket(f, &f->hash[i]);
@@ -174,7 +188,8 @@
f->next_bucket = i;
- read_unlock_bh(&f->lock);
+ local_bh_enable();
+
if (f->rebuild && inet_frag_may_rebuild(f))
inet_frag_secret_rebuild(f);
}
@@ -197,7 +212,8 @@
spin_lock_init(&hb->chain_lock);
INIT_HLIST_HEAD(&hb->chain);
}
- rwlock_init(&f->lock);
+
+ seqlock_init(&f->rnd_seqlock);
f->last_rebuild_jiffies = 0;
}
EXPORT_SYMBOL(inet_frags_init);
@@ -216,35 +232,56 @@
void inet_frags_exit_net(struct netns_frags *nf, struct inet_frags *f)
{
+ unsigned int seq;
int i;
nf->low_thresh = 0;
+ local_bh_disable();
- read_lock_bh(&f->lock);
+evict_again:
+ seq = read_seqbegin(&f->rnd_seqlock);
for (i = 0; i < INETFRAGS_HASHSZ ; i++)
inet_evict_bucket(f, &f->hash[i]);
- read_unlock_bh(&f->lock);
+ if (read_seqretry(&f->rnd_seqlock, seq))
+ goto evict_again;
+
+ local_bh_enable();
percpu_counter_destroy(&nf->mem);
}
EXPORT_SYMBOL(inet_frags_exit_net);
-static inline void fq_unlink(struct inet_frag_queue *fq, struct inet_frags *f)
+static struct inet_frag_bucket *
+get_frag_bucket_locked(struct inet_frag_queue *fq, struct inet_frags *f)
+__acquires(hb->chain_lock)
{
struct inet_frag_bucket *hb;
- unsigned int hash;
+ unsigned int seq, hash;
- read_lock(&f->lock);
+ restart:
+ seq = read_seqbegin(&f->rnd_seqlock);
+
hash = inet_frag_hashfn(f, fq);
hb = &f->hash[hash];
spin_lock(&hb->chain_lock);
+ if (read_seqretry(&f->rnd_seqlock, seq)) {
+ spin_unlock(&hb->chain_lock);
+ goto restart;
+ }
+
+ return hb;
+}
+
+static inline void fq_unlink(struct inet_frag_queue *fq, struct inet_frags *f)
+{
+ struct inet_frag_bucket *hb;
+
+ hb = get_frag_bucket_locked(fq, f);
hlist_del(&fq->list);
spin_unlock(&hb->chain_lock);
-
- read_unlock(&f->lock);
}
void inet_frag_kill(struct inet_frag_queue *fq, struct inet_frags *f)
@@ -300,30 +337,18 @@
struct inet_frag_queue *qp_in, struct inet_frags *f,
void *arg)
{
- struct inet_frag_bucket *hb;
+ struct inet_frag_bucket *hb = get_frag_bucket_locked(qp_in, f);
struct inet_frag_queue *qp;
- unsigned int hash;
-
- read_lock(&f->lock); /* Protects against hash rebuild */
- /*
- * While we stayed w/o the lock other CPU could update
- * the rnd seed, so we need to re-calculate the hash
- * chain. Fortunatelly the qp_in can be used to get one.
- */
- hash = inet_frag_hashfn(f, qp_in);
- hb = &f->hash[hash];
- spin_lock(&hb->chain_lock);
#ifdef CONFIG_SMP
/* With SMP race we have to recheck hash table, because
- * such entry could be created on other cpu, while we
- * released the hash bucket lock.
+ * such entry could have been created on other cpu before
+ * we acquired hash bucket lock.
*/
hlist_for_each_entry(qp, &hb->chain, list) {
if (qp->net == nf && f->match(qp, arg)) {
atomic_inc(&qp->refcnt);
spin_unlock(&hb->chain_lock);
- read_unlock(&f->lock);
qp_in->last_in |= INET_FRAG_COMPLETE;
inet_frag_put(qp_in, f);
return qp;
@@ -338,7 +363,6 @@
hlist_add_head(&qp->list, &hb->chain);
spin_unlock(&hb->chain_lock);
- read_unlock(&f->lock);
return qp;
}
@@ -382,7 +406,6 @@
struct inet_frag_queue *inet_frag_find(struct netns_frags *nf,
struct inet_frags *f, void *key, unsigned int hash)
- __releases(&f->lock)
{
struct inet_frag_bucket *hb;
struct inet_frag_queue *q;
@@ -399,19 +422,18 @@
if (q->net == nf && f->match(q, key)) {
atomic_inc(&q->refcnt);
spin_unlock(&hb->chain_lock);
- read_unlock(&f->lock);
return q;
}
depth++;
}
spin_unlock(&hb->chain_lock);
- read_unlock(&f->lock);
if (depth <= INETFRAGS_MAXDEPTH)
return inet_frag_create(nf, f, key);
if (inet_frag_may_rebuild(f)) {
- f->rebuild = true;
+ if (!f->rebuild)
+ f->rebuild = true;
inet_frag_schedule_worker(f);
}
diff --git a/net/ipv4/ip_fragment.c b/net/ipv4/ip_fragment.c
index 44e591a..ccee68d 100644
--- a/net/ipv4/ip_fragment.c
+++ b/net/ipv4/ip_fragment.c
@@ -244,7 +244,6 @@
arg.iph = iph;
arg.user = user;
- read_lock(&ip4_frags.lock);
hash = ipqhashfn(iph->id, iph->saddr, iph->daddr, iph->protocol);
q = inet_frag_find(&net->ipv4.frags, &ip4_frags, &arg, hash);
diff --git a/net/ipv6/netfilter/nf_conntrack_reasm.c b/net/ipv6/netfilter/nf_conntrack_reasm.c
index 3b3ef97..4d9da1e 100644
--- a/net/ipv6/netfilter/nf_conntrack_reasm.c
+++ b/net/ipv6/netfilter/nf_conntrack_reasm.c
@@ -193,7 +193,7 @@
arg.dst = dst;
arg.ecn = ecn;
- read_lock_bh(&nf_frags.lock);
+ local_bh_disable();
hash = nf_hash_frag(id, src, dst);
q = inet_frag_find(&net->nf_frag.frags, &nf_frags, &arg, hash);
diff --git a/net/ipv6/reassembly.c b/net/ipv6/reassembly.c
index 987fea4..57a9707 100644
--- a/net/ipv6/reassembly.c
+++ b/net/ipv6/reassembly.c
@@ -190,7 +190,6 @@
arg.dst = dst;
arg.ecn = ecn;
- read_lock(&ip6_frags.lock);
hash = inet6_hash_frag(id, src, dst);
q = inet_frag_find(&net->ipv6.frags, &ip6_frags, &arg, hash);
