[PATCH bpf-next v7 07/17] bpf: Remove cgroup local storage percpu counter

[Amery Hung <ameryhung@gmail.com>]

The percpu counter in cgroup local storage is no longer needed as the
underlying bpf_local_storage can now handle deadlock with the help of
rqspinlock. Remove the percpu counter and related migrate_{disable,
enable}.

Signed-off-by: Amery Hung <ameryhung@gmail.com>
---
 kernel/bpf/bpf_cgrp_storage.c | 59 +++++------------------------------
 1 file changed, 8 insertions(+), 51 deletions(-)

diff --git a/kernel/bpf/bpf_cgrp_storage.c b/kernel/bpf/bpf_cgrp_storage.c
index 8fef24fcac68..4d84611d8222 100644
--- a/kernel/bpf/bpf_cgrp_storage.c
+++ b/kernel/bpf/bpf_cgrp_storage.c
@@ -11,29 +11,6 @@
 
 DEFINE_BPF_STORAGE_CACHE(cgroup_cache);
 
-static DEFINE_PER_CPU(int, bpf_cgrp_storage_busy);
-
-static void bpf_cgrp_storage_lock(void)
-{
-	cant_migrate();
-	this_cpu_inc(bpf_cgrp_storage_busy);
-}
-
-static void bpf_cgrp_storage_unlock(void)
-{
-	this_cpu_dec(bpf_cgrp_storage_busy);
-}
-
-static bool bpf_cgrp_storage_trylock(void)
-{
-	cant_migrate();
-	if (unlikely(this_cpu_inc_return(bpf_cgrp_storage_busy) != 1)) {
-		this_cpu_dec(bpf_cgrp_storage_busy);
-		return false;
-	}
-	return true;
-}
-
 static struct bpf_local_storage __rcu **cgroup_storage_ptr(void *owner)
 {
 	struct cgroup *cg = owner;
@@ -45,16 +22,14 @@ void bpf_cgrp_storage_free(struct cgroup *cgroup)
 {
 	struct bpf_local_storage *local_storage;
 
-	rcu_read_lock_dont_migrate();
+	rcu_read_lock();
 	local_storage = rcu_dereference(cgroup->bpf_cgrp_storage);
 	if (!local_storage)
 		goto out;
 
-	bpf_cgrp_storage_lock();
 	bpf_local_storage_destroy(local_storage);
-	bpf_cgrp_storage_unlock();
 out:
-	rcu_read_unlock_migrate();
+	rcu_read_unlock();
 }
 
 static struct bpf_local_storage_data *
@@ -83,9 +58,7 @@ static void *bpf_cgrp_storage_lookup_elem(struct bpf_map *map, void *key)
 	if (IS_ERR(cgroup))
 		return ERR_CAST(cgroup);
 
-	bpf_cgrp_storage_lock();
 	sdata = cgroup_storage_lookup(cgroup, map, true);
-	bpf_cgrp_storage_unlock();
 	cgroup_put(cgroup);
 	return sdata ? sdata->data : NULL;
 }
@@ -102,10 +75,8 @@ static long bpf_cgrp_storage_update_elem(struct bpf_map *map, void *key,
 	if (IS_ERR(cgroup))
 		return PTR_ERR(cgroup);
 
-	bpf_cgrp_storage_lock();
 	sdata = bpf_local_storage_update(cgroup, (struct bpf_local_storage_map *)map,
 					 value, map_flags, false, GFP_ATOMIC);
-	bpf_cgrp_storage_unlock();
 	cgroup_put(cgroup);
 	return PTR_ERR_OR_ZERO(sdata);
 }
@@ -131,9 +102,7 @@ static long bpf_cgrp_storage_delete_elem(struct bpf_map *map, void *key)
 	if (IS_ERR(cgroup))
 		return PTR_ERR(cgroup);
 
-	bpf_cgrp_storage_lock();
 	err = cgroup_storage_delete(cgroup, map);
-	bpf_cgrp_storage_unlock();
 	cgroup_put(cgroup);
 	return err;
 }
@@ -150,7 +119,7 @@ static struct bpf_map *cgroup_storage_map_alloc(union bpf_attr *attr)
 
 static void cgroup_storage_map_free(struct bpf_map *map)
 {
-	bpf_local_storage_map_free(map, &cgroup_cache, &bpf_cgrp_storage_busy);
+	bpf_local_storage_map_free(map, &cgroup_cache, NULL);
 }
 
 /* *gfp_flags* is a hidden argument provided by the verifier */
@@ -158,7 +127,6 @@ BPF_CALL_5(bpf_cgrp_storage_get, struct bpf_map *, map, struct cgroup *, cgroup,
 	   void *, value, u64, flags, gfp_t, gfp_flags)
 {
 	struct bpf_local_storage_data *sdata;
-	bool nobusy;
 
 	WARN_ON_ONCE(!bpf_rcu_lock_held());
 	if (flags & ~(BPF_LOCAL_STORAGE_GET_F_CREATE))
@@ -167,38 +135,27 @@ BPF_CALL_5(bpf_cgrp_storage_get, struct bpf_map *, map, struct cgroup *, cgroup,
 	if (!cgroup)
 		return (unsigned long)NULL;
 
-	nobusy = bpf_cgrp_storage_trylock();
-
-	sdata = cgroup_storage_lookup(cgroup, map, nobusy);
+	sdata = cgroup_storage_lookup(cgroup, map, true);
 	if (sdata)
-		goto unlock;
+		goto out;
 
 	/* only allocate new storage, when the cgroup is refcounted */
 	if (!percpu_ref_is_dying(&cgroup->self.refcnt) &&
-	    (flags & BPF_LOCAL_STORAGE_GET_F_CREATE) && nobusy)
+	    (flags & BPF_LOCAL_STORAGE_GET_F_CREATE))
 		sdata = bpf_local_storage_update(cgroup, (struct bpf_local_storage_map *)map,
 						 value, BPF_NOEXIST, false, gfp_flags);
 
-unlock:
-	if (nobusy)
-		bpf_cgrp_storage_unlock();
+out:
 	return IS_ERR_OR_NULL(sdata) ? (unsigned long)NULL : (unsigned long)sdata->data;
 }
 
 BPF_CALL_2(bpf_cgrp_storage_delete, struct bpf_map *, map, struct cgroup *, cgroup)
 {
-	int ret;
-
 	WARN_ON_ONCE(!bpf_rcu_lock_held());
 	if (!cgroup)
 		return -EINVAL;
 
-	if (!bpf_cgrp_storage_trylock())
-		return -EBUSY;
-
-	ret = cgroup_storage_delete(cgroup, map);
-	bpf_cgrp_storage_unlock();
-	return ret;
+	return cgroup_storage_delete(cgroup, map);
 }
 
 const struct bpf_map_ops cgrp_storage_map_ops = {
-- 
2.47.3