net: sched: RCU cls_tcindex

Make cls_tcindex RCU safe.

This patch addds a new RCU routine rcu_dereference_bh_rtnl() to check
caller either holds the rcu read lock or RTNL. This is needed to
handle the case where tcindex_lookup() is being called in both cases.

Signed-off-by: John Fastabend <john.r.fastabend@intel.com>
Acked-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 154 insertions, 94 deletions

diff --git a/net/sched/cls_tcindex.c b/net/sched/cls_tcindex.c
index 3e9f76413b3b..a9f4279fbd69 100644
--- a/net/sched/cls_tcindex.c
+++ b/net/sched/cls_tcindex.c
@@ -32,19 +32,21 @@ struct tcindex_filter_result {
 struct tcindex_filter {
         u16 key;
         struct tcindex_filter_result result;
-        struct tcindex_filter *next;
+        struct tcindex_filter __rcu *next;
+        struct rcu_head rcu;
 };
 
 
 struct tcindex_data {
         struct tcindex_filter_result *perfect; /* perfect hash; NULL if none */
-        struct tcindex_filter **h; /* imperfect hash; only used if !perfect;
-                                      NULL if unused */
+        struct tcindex_filter __rcu **h; /* imperfect hash; */
+        struct tcf_proto *tp;
         u16 mask;               /* AND key with mask */
-        int shift;              /* shift ANDed key to the right */
-        int hash;               /* hash table size; 0 if undefined */
-        int alloc_hash;         /* allocated size */
-        int fall_through;       /* 0: only classify if explicit match */
+        u32 shift;              /* shift ANDed key to the right */
+        u32 hash;               /* hash table size; 0 if undefined */
+        u32 alloc_hash;         /* allocated size */
+        u32 fall_through;       /* 0: only classify if explicit match */
+        struct rcu_head rcu;
 };
 
 static inline int
@@ -56,13 +58,18 @@ tcindex_filter_is_set(struct tcindex_filter_result *r)
 static struct tcindex_filter_result *
 tcindex_lookup(struct tcindex_data *p, u16 key)
 {
-        struct tcindex_filter *f;
+        if (p->perfect) {
+                struct tcindex_filter_result *f = p->perfect + key;
+
+                return tcindex_filter_is_set(f) ? f : NULL;
+        } else if (p->h) {
+                struct tcindex_filter __rcu **fp;
+                struct tcindex_filter *f;
 
-        if (p->perfect)
-                return tcindex_filter_is_set(p->perfect + key) ?
-                        p->perfect + key : NULL;
-        else if (p->h) {
-                for (f = p->h[key % p->hash]; f; f = f->next)
+                fp = &p->h[key % p->hash];
+                for (f = rcu_dereference_bh_rtnl(*fp);
+                     f;
+                     fp = &f->next, f = rcu_dereference_bh_rtnl(*fp))
                         if (f->key == key)
                                 return &f->result;
         }
@@ -74,7 +81,7 @@ tcindex_lookup(struct tcindex_data *p, u16 key)
 static int tcindex_classify(struct sk_buff *skb, const struct tcf_proto *tp,
                             struct tcf_result *res)
 {
-        struct tcindex_data *p = tp->root;
+        struct tcindex_data *p = rcu_dereference(tp->root);
         struct tcindex_filter_result *f;
         int key = (skb->tc_index & p->mask) >> p->shift;
 
@@ -99,7 +106,7 @@ static int tcindex_classify(struct sk_buff *skb, const struct tcf_proto *tp,
 
 static unsigned long tcindex_get(struct tcf_proto *tp, u32 handle)
 {
-        struct tcindex_data *p = tp->root;
+        struct tcindex_data *p = rtnl_dereference(tp->root);
         struct tcindex_filter_result *r;
 
         pr_debug("tcindex_get(tp %p,handle 0x%08x)\n", tp, handle);
@@ -129,49 +136,59 @@ static int tcindex_init(struct tcf_proto *tp)
         p->hash = DEFAULT_HASH_SIZE;
         p->fall_through = 1;
 
-        tp->root = p;
+        rcu_assign_pointer(tp->root, p);
         return 0;
 }
 
-
 static int
-__tcindex_delete(struct tcf_proto *tp, unsigned long arg, int lock)
+tcindex_delete(struct tcf_proto *tp, unsigned long arg)
 {
-        struct tcindex_data *p = tp->root;
+        struct tcindex_data *p = rtnl_dereference(tp->root);
         struct tcindex_filter_result *r = (struct tcindex_filter_result *) arg;
+        struct tcindex_filter __rcu **walk;
         struct tcindex_filter *f = NULL;
 
-        pr_debug("tcindex_delete(tp %p,arg 0x%lx),p %p,f %p\n", tp, arg, p, f);
+        pr_debug("tcindex_delete(tp %p,arg 0x%lx),p %p\n", tp, arg, p);
         if (p->perfect) {
                 if (!r->res.class)
                         return -ENOENT;
         } else {
                 int i;
-                struct tcindex_filter **walk = NULL;
 
-                for (i = 0; i < p->hash; i++)
-                        for (walk = p->h+i; *walk; walk = &(*walk)->next)
-                                if (&(*walk)->result == r)
+                for (i = 0; i < p->hash; i++) {
+                        walk = p->h + i;
+                        for (f = rtnl_dereference(*walk); f;
+                             walk = &f->next, f = rtnl_dereference(*walk)) {
+                                if (&f->result == r)
                                         goto found;
+                        }
+                }
                 return -ENOENT;
 
 found:
-                f = *walk;
-                if (lock)
-                        tcf_tree_lock(tp);
-                *walk = f->next;
-                if (lock)
-                        tcf_tree_unlock(tp);
+                rcu_assign_pointer(*walk, rtnl_dereference(f->next));
         }
         tcf_unbind_filter(tp, &r->res);
         tcf_exts_destroy(tp, &r->exts);
-        kfree(f);
+        if (f)
+                kfree_rcu(f, rcu);
         return 0;
 }
 
-static int tcindex_delete(struct tcf_proto *tp, unsigned long arg)
+static int tcindex_destroy_element(struct tcf_proto *tp,
+                                   unsigned long arg,
+                                   struct tcf_walker *walker)
 {
-        return __tcindex_delete(tp, arg, 1);
+        return tcindex_delete(tp, arg);
+}
+
+static void __tcindex_destroy(struct rcu_head *head)
+{
+        struct tcindex_data *p = container_of(head, struct tcindex_data, rcu);
+
+        kfree(p->perfect);
+        kfree(p->h);
+        kfree(p);
 }
 
 static inline int
@@ -194,6 +211,14 @@ static void tcindex_filter_result_init(struct tcindex_filter_result *r)
         tcf_exts_init(&r->exts, TCA_TCINDEX_ACT, TCA_TCINDEX_POLICE);
 }
 
+static void __tcindex_partial_destroy(struct rcu_head *head)
+{
+        struct tcindex_data *p = container_of(head, struct tcindex_data, rcu);
+
+        kfree(p->perfect);
+        kfree(p);
+}
+
 static int
 tcindex_set_parms(struct net *net, struct tcf_proto *tp, unsigned long base,
                   u32 handle, struct tcindex_data *p,
@@ -203,7 +228,7 @@ tcindex_set_parms(struct net *net, struct tcf_proto *tp, unsigned long base,
         int err, balloc = 0;
         struct tcindex_filter_result new_filter_result, *old_r = r;
         struct tcindex_filter_result cr;
-        struct tcindex_data cp;
+        struct tcindex_data *cp, *oldp;
         struct tcindex_filter *f = NULL; /* make gcc behave */
         struct tcf_exts e;
 
@@ -212,84 +237,118 @@ tcindex_set_parms(struct net *net, struct tcf_proto *tp, unsigned long base,
         if (err < 0)
                 return err;
 
-        memcpy(&cp, p, sizeof(cp));
-        tcindex_filter_result_init(&new_filter_result);
+        /* tcindex_data attributes must look atomic to classifier/lookup so
+         * allocate new tcindex data and RCU assign it onto root. Keeping
+         * perfect hash and hash pointers from old data.
+         */
+        cp = kzalloc(sizeof(cp), GFP_KERNEL);
+        if (!cp)
+                return -ENOMEM;
+
+        cp->mask = p->mask;
+        cp->shift = p->shift;
+        cp->hash = p->hash;
+        cp->alloc_hash = p->alloc_hash;
+        cp->fall_through = p->fall_through;
+        cp->tp = tp;
+
+        if (p->perfect) {
+                cp->perfect = kmemdup(p->perfect,
+                                      sizeof(*r) * cp->hash, GFP_KERNEL);
+                if (!cp->perfect)
+                        goto errout;
+        }
+        cp->h = p->h;
+
+        memset(&new_filter_result, 0, sizeof(new_filter_result));
+        tcf_exts_init(&new_filter_result.exts,
+                      TCA_TCINDEX_ACT, TCA_TCINDEX_POLICE);
 
         tcindex_filter_result_init(&cr);
         if (old_r)
                 cr.res = r->res;
 
         if (tb[TCA_TCINDEX_HASH])
-                cp.hash = nla_get_u32(tb[TCA_TCINDEX_HASH]);
+                cp->hash = nla_get_u32(tb[TCA_TCINDEX_HASH]);
 
         if (tb[TCA_TCINDEX_MASK])
-                cp.mask = nla_get_u16(tb[TCA_TCINDEX_MASK]);
+                cp->mask = nla_get_u16(tb[TCA_TCINDEX_MASK]);
 
         if (tb[TCA_TCINDEX_SHIFT])
-                cp.shift = nla_get_u32(tb[TCA_TCINDEX_SHIFT]);
+                cp->shift = nla_get_u32(tb[TCA_TCINDEX_SHIFT]);
 
         err = -EBUSY;
+
         /* Hash already allocated, make sure that we still meet the
          * requirements for the allocated hash.
          */
-        if (cp.perfect) {
-                if (!valid_perfect_hash(&cp) ||
-                    cp.hash > cp.alloc_hash)
+        if (cp->perfect) {
+                if (!valid_perfect_hash(cp) ||
+                    cp->hash > cp->alloc_hash)
                         goto errout;
-        } else if (cp.h && cp.hash != cp.alloc_hash)
+        } else if (cp->h && cp->hash != cp->alloc_hash) {
                 goto errout;
+        }
 
         err = -EINVAL;
         if (tb[TCA_TCINDEX_FALL_THROUGH])
-                cp.fall_through = nla_get_u32(tb[TCA_TCINDEX_FALL_THROUGH]);
+                cp->fall_through = nla_get_u32(tb[TCA_TCINDEX_FALL_THROUGH]);
 
-        if (!cp.hash) {
+        if (!cp->hash) {
                 /* Hash not specified, use perfect hash if the upper limit
                  * of the hashing index is below the threshold.
                  */
-                if ((cp.mask >> cp.shift) < PERFECT_HASH_THRESHOLD)
-                        cp.hash = (cp.mask >> cp.shift) + 1;
+                if ((cp->mask >> cp->shift) < PERFECT_HASH_THRESHOLD)
+                        cp->hash = (cp->mask >> cp->shift) + 1;
                 else
-                        cp.hash = DEFAULT_HASH_SIZE;
+                        cp->hash = DEFAULT_HASH_SIZE;
         }
 
-        if (!cp.perfect && !cp.h)
-                cp.alloc_hash = cp.hash;
+        if (!cp->perfect && cp->h)
+                cp->alloc_hash = cp->hash;
 
         /* Note: this could be as restrictive as if (handle & ~(mask >> shift))
          * but then, we'd fail handles that may become valid after some future
          * mask change. While this is extremely unlikely to ever matter,
          * the check below is safer (and also more backwards-compatible).
          */
-        if (cp.perfect || valid_perfect_hash(&cp))
-                if (handle >= cp.alloc_hash)
+        if (cp->perfect || valid_perfect_hash(cp))
+                if (handle >= cp->alloc_hash)
                         goto errout;
 
 
         err = -ENOMEM;
-        if (!cp.perfect && !cp.h) {
-                if (valid_perfect_hash(&cp)) {
+        if (!cp->perfect && !cp->h) {
+                if (valid_perfect_hash(cp)) {
                         int i;
 
-                        cp.perfect = kcalloc(cp.hash, sizeof(*r), GFP_KERNEL);
-                        if (!cp.perfect)
+                        cp->perfect = kcalloc(cp->hash, sizeof(*r), GFP_KERNEL);
+                        if (!cp->perfect)
                                 goto errout;
-                        for (i = 0; i < cp.hash; i++)
-                                tcf_exts_init(&cp.perfect[i].exts, TCA_TCINDEX_ACT,
+                        for (i = 0; i < cp->hash; i++)
+                                tcf_exts_init(&cp->perfect[i].exts,
+                                              TCA_TCINDEX_ACT,
                                               TCA_TCINDEX_POLICE);
                         balloc = 1;
                 } else {
-                        cp.h = kcalloc(cp.hash, sizeof(f), GFP_KERNEL);
-                        if (!cp.h)
+                        struct tcindex_filter __rcu **hash;
+
+                        hash = kcalloc(cp->hash,
+                                       sizeof(struct tcindex_filter *),
+                                       GFP_KERNEL);
+
+                        if (!hash)
                                 goto errout;
+
+                        cp->h = hash;
                         balloc = 2;
                 }
         }
 
-        if (cp.perfect)
-                r = cp.perfect + handle;
+        if (cp->perfect)
+                r = cp->perfect + handle;
         else
-                r = tcindex_lookup(&cp, handle) ? : &new_filter_result;
+                r = tcindex_lookup(cp, handle) ? : &new_filter_result;
 
         if (r == &new_filter_result) {
                 f = kzalloc(sizeof(*f), GFP_KERNEL);
@@ -307,33 +366,41 @@ tcindex_set_parms(struct net *net, struct tcf_proto *tp, unsigned long base,
         else
                 tcf_exts_change(tp, &cr.exts, &e);
 
-        tcf_tree_lock(tp);
         if (old_r && old_r != r)
                 tcindex_filter_result_init(old_r);
 
-        memcpy(p, &cp, sizeof(cp));
+        oldp = p;
         r->res = cr.res;
+        rcu_assign_pointer(tp->root, cp);
 
         if (r == &new_filter_result) {
-                struct tcindex_filter **fp;
+                struct tcindex_filter *nfp;
+                struct tcindex_filter __rcu **fp;
 
                 f->key = handle;
                 f->result = new_filter_result;
                 f->next = NULL;
-                for (fp = p->h+(handle % p->hash); *fp; fp = &(*fp)->next)
-                        /* nothing */;
-                *fp = f;
+
+                fp = p->h + (handle % p->hash);
+                for (nfp = rtnl_dereference(*fp);
+                     nfp;
+                     fp = &nfp->next, nfp = rtnl_dereference(*fp))
+                                ; /* nothing */
+
+                rcu_assign_pointer(*fp, f);
         }
-        tcf_tree_unlock(tp);
 
+        if (oldp)
+                call_rcu(&oldp->rcu, __tcindex_partial_destroy);
         return 0;
 
 errout_alloc:
         if (balloc == 1)
-                kfree(cp.perfect);
+                kfree(cp->perfect);
         else if (balloc == 2)
-                kfree(cp.h);
+                kfree(cp->h);
 errout:
+        kfree(cp);
         tcf_exts_destroy(tp, &e);
         return err;
 }
@@ -345,7 +412,7 @@ tcindex_change(struct net *net, struct sk_buff *in_skb,
 {
         struct nlattr *opt = tca[TCA_OPTIONS];
         struct nlattr *tb[TCA_TCINDEX_MAX + 1];
-        struct tcindex_data *p = tp->root;
+        struct tcindex_data *p = rtnl_dereference(tp->root);
         struct tcindex_filter_result *r = (struct tcindex_filter_result *) *arg;
         int err;
 
@@ -364,10 +431,9 @@ tcindex_change(struct net *net, struct sk_buff *in_skb,
                                  tca[TCA_RATE], ovr);
 }
 
-
 static void tcindex_walk(struct tcf_proto *tp, struct tcf_walker *walker)
 {
-        struct tcindex_data *p = tp->root;
+        struct tcindex_data *p = rtnl_dereference(tp->root);
         struct tcindex_filter *f, *next;
         int i;
 
@@ -390,8 +456,8 @@ static void tcindex_walk(struct tcf_proto *tp, struct tcf_walker *walker)
         if (!p->h)
                 return;
         for (i = 0; i < p->hash; i++) {
-                for (f = p->h[i]; f; f = next) {
-                        next = f->next;
+                for (f = rtnl_dereference(p->h[i]); f; f = next) {
+                        next = rtnl_dereference(f->next);
                         if (walker->count >= walker->skip) {
                                 if (walker->fn(tp, (unsigned long) &f->result,
                                     walker) < 0) {
@@ -404,17 +470,9 @@ static void tcindex_walk(struct tcf_proto *tp, struct tcf_walker *walker)
         }
 }
 
-
-static int tcindex_destroy_element(struct tcf_proto *tp,
-    unsigned long arg, struct tcf_walker *walker)
-{
-        return __tcindex_delete(tp, arg, 0);
-}
-
-
 static void tcindex_destroy(struct tcf_proto *tp)
 {
-        struct tcindex_data *p = tp->root;
+        struct tcindex_data *p = rtnl_dereference(tp->root);
         struct tcf_walker walker;
 
         pr_debug("tcindex_destroy(tp %p),p %p\n", tp, p);
@@ -422,17 +480,16 @@ static void tcindex_destroy(struct tcf_proto *tp)
         walker.skip = 0;
         walker.fn = tcindex_destroy_element;
         tcindex_walk(tp, &walker);
-        kfree(p->perfect);
-        kfree(p->h);
-        kfree(p);
-        tp->root = NULL;
+
+        RCU_INIT_POINTER(tp->root, NULL);
+        call_rcu(&p->rcu, __tcindex_destroy);
 }
 
 
 static int tcindex_dump(struct net *net, struct tcf_proto *tp, unsigned long fh,
     struct sk_buff *skb, struct tcmsg *t)
 {
-        struct tcindex_data *p = tp->root;
+        struct tcindex_data *p = rtnl_dereference(tp->root);
         struct tcindex_filter_result *r = (struct tcindex_filter_result *) fh;
         unsigned char *b = skb_tail_pointer(skb);
         struct nlattr *nest;
@@ -455,15 +512,18 @@ static int tcindex_dump(struct net *net, struct tcf_proto *tp, unsigned long fh,
                 nla_nest_end(skb, nest);
         } else {
                 if (p->perfect) {
-                        t->tcm_handle = r-p->perfect;
+                        t->tcm_handle = r - p->perfect;
                 } else {
                         struct tcindex_filter *f;
+                        struct tcindex_filter __rcu **fp;
                         int i;
 
                         t->tcm_handle = 0;
                         for (i = 0; !t->tcm_handle && i < p->hash; i++) {
-                                for (f = p->h[i]; !t->tcm_handle && f;
-                                     f = f->next) {
+                                fp = &p->h[i];
+                                for (f = rtnl_dereference(*fp);
+                                     !t->tcm_handle && f;
+                                     fp = &f->next, f = rtnl_dereference(*fp)) {
                                         if (&f->result == r)
                                                 t->tcm_handle = f->key;
                                 }