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Fri, 30 Jan 2026 21:09:34 -0800 (PST) Received: from localhost ([2a03:2880:ff:7::]) by smtp.gmail.com with ESMTPSA id d9443c01a7336-2a88b7f32bfsm94863945ad.96.2026.01.30.21.09.33 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 30 Jan 2026 21:09:34 -0800 (PST) From: Amery Hung To: bpf@vger.kernel.org Cc: netdev@vger.kernel.org, alexei.starovoitov@gmail.com, andrii@kernel.org, daniel@iogearbox.net, memxor@gmail.com, martin.lau@kernel.org, kpsingh@kernel.org, yonghong.song@linux.dev, song@kernel.org, haoluo@google.com, ameryhung@gmail.com, kernel-team@meta.com Subject: [PATCH bpf-next v4 11/16] bpf: Switch to bpf_selem_unlink_nofail in bpf_local_storage_{map_free, destroy} Date: Fri, 30 Jan 2026 21:09:14 -0800 Message-ID: <20260131050920.2574084-12-ameryhung@gmail.com> X-Mailer: git-send-email 2.47.3 In-Reply-To: <20260131050920.2574084-1-ameryhung@gmail.com> References: <20260131050920.2574084-1-ameryhung@gmail.com> Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Take care of rqspinlock error in bpf_local_storage_{map_free, destroy}() properly by switching to bpf_selem_unlink_nofail(). Both functions iterate their own RCU-protected list of selems and call bpf_selem_unlink_nofail(). In map_free(), to prevent infinite loop when both map_free() and destroy() fail to remove a selem from b->list (extremely unlikely), switch to hlist_for_each_entry_rcu(). In destroy(), also switch to hlist_for_each_entry_rcu() since we no longer iterate local_storage->list under local_storage->lock. In addition, defer it to workqueue as sleep may not always be possible in destroy(). Since selem, SDATA(selem)->smap and selem->local_storage may be seen by map_free() and destroy() at the same time, protect them with RCU. This means passing reuse_now == false to bpf_selem_free() and bpf_local_storage_free(). The local storage map is already protected as bpf_local_storage_map_free() waits for an RCU grace period after iterating b->list and before freeing itself. bpf_selem_unlink() now becomes dedicated to helpers and syscalls paths so reuse_now should always be false. Remove it from the argument and hardcode it. Co-developed-by: Martin KaFai Lau Signed-off-by: Martin KaFai Lau Signed-off-by: Amery Hung --- include/linux/bpf_local_storage.h | 5 +- kernel/bpf/bpf_cgrp_storage.c | 3 +- kernel/bpf/bpf_inode_storage.c | 3 +- kernel/bpf/bpf_local_storage.c | 96 +++++++++++++++++-------------- kernel/bpf/bpf_task_storage.c | 3 +- net/core/bpf_sk_storage.c | 9 ++- 6 files changed, 69 insertions(+), 50 deletions(-) diff --git a/include/linux/bpf_local_storage.h b/include/linux/bpf_local_storage.h index 4e1ebfb3b9e8..605590a8f98d 100644 --- a/include/linux/bpf_local_storage.h +++ b/include/linux/bpf_local_storage.h @@ -101,6 +101,7 @@ struct bpf_local_storage { rqspinlock_t lock; /* Protect adding/removing from the "list" */ u64 selems_size; /* Total selem size. Protected by "lock" */ refcount_t owner_refcnt; + struct work_struct work; bool use_kmalloc_nolock; }; @@ -168,7 +169,7 @@ bpf_local_storage_lookup(struct bpf_local_storage *local_storage, return SDATA(selem); } -void bpf_local_storage_destroy(struct bpf_local_storage *local_storage); +u32 bpf_local_storage_destroy(struct bpf_local_storage *local_storage); void bpf_local_storage_map_free(struct bpf_map *map, struct bpf_local_storage_cache *cache); @@ -181,7 +182,7 @@ int bpf_local_storage_map_check_btf(const struct bpf_map *map, void bpf_selem_link_storage_nolock(struct bpf_local_storage *local_storage, struct bpf_local_storage_elem *selem); -int bpf_selem_unlink(struct bpf_local_storage_elem *selem, bool reuse_now); +int bpf_selem_unlink(struct bpf_local_storage_elem *selem); int bpf_selem_link_map(struct bpf_local_storage_map *smap, struct bpf_local_storage_elem *selem); diff --git a/kernel/bpf/bpf_cgrp_storage.c b/kernel/bpf/bpf_cgrp_storage.c index 853183eead2c..0bc3ab19c7b4 100644 --- a/kernel/bpf/bpf_cgrp_storage.c +++ b/kernel/bpf/bpf_cgrp_storage.c @@ -27,6 +27,7 @@ void bpf_cgrp_storage_free(struct cgroup *cgroup) if (!local_storage) goto out; + RCU_INIT_POINTER(cgroup->bpf_cgrp_storage, NULL); bpf_local_storage_destroy(local_storage); out: rcu_read_unlock(); @@ -89,7 +90,7 @@ static int cgroup_storage_delete(struct cgroup *cgroup, struct bpf_map *map) if (!sdata) return -ENOENT; - return bpf_selem_unlink(SELEM(sdata), false); + return bpf_selem_unlink(SELEM(sdata)); } static long bpf_cgrp_storage_delete_elem(struct bpf_map *map, void *key) diff --git a/kernel/bpf/bpf_inode_storage.c b/kernel/bpf/bpf_inode_storage.c index 470f4b02c79e..eb607156ba35 100644 --- a/kernel/bpf/bpf_inode_storage.c +++ b/kernel/bpf/bpf_inode_storage.c @@ -68,6 +68,7 @@ void bpf_inode_storage_free(struct inode *inode) if (!local_storage) goto out; + RCU_INIT_POINTER(bsb->storage, NULL); bpf_local_storage_destroy(local_storage); out: rcu_read_unlock_migrate(); @@ -110,7 +111,7 @@ static int inode_storage_delete(struct inode *inode, struct bpf_map *map) if (!sdata) return -ENOENT; - return bpf_selem_unlink(SELEM(sdata), false); + return bpf_selem_unlink(SELEM(sdata)); } static long bpf_fd_inode_storage_delete_elem(struct bpf_map *map, void *key) diff --git a/kernel/bpf/bpf_local_storage.c b/kernel/bpf/bpf_local_storage.c index 54d106ebbfe5..364198959053 100644 --- a/kernel/bpf/bpf_local_storage.c +++ b/kernel/bpf/bpf_local_storage.c @@ -383,7 +383,11 @@ static void bpf_selem_link_map_nolock(struct bpf_local_storage_map_bucket *b, hlist_add_head_rcu(&selem->map_node, &b->list); } -int bpf_selem_unlink(struct bpf_local_storage_elem *selem, bool reuse_now) +/* + * Unlink an selem from map and local storage with lock held. + * This is the common path used by local storages to delete an selem. + */ +int bpf_selem_unlink(struct bpf_local_storage_elem *selem) { struct bpf_local_storage *local_storage; bool free_local_storage = false; @@ -417,10 +421,10 @@ int bpf_selem_unlink(struct bpf_local_storage_elem *selem, bool reuse_now) out: raw_res_spin_unlock_irqrestore(&local_storage->lock, flags); - bpf_selem_free_list(&selem_free_list, reuse_now); + bpf_selem_free_list(&selem_free_list, false); if (free_local_storage) - bpf_local_storage_free(local_storage, reuse_now); + bpf_local_storage_free(local_storage, false); return err; } @@ -650,7 +654,7 @@ bpf_local_storage_update(void *owner, struct bpf_local_storage_map *smap, local_storage = rcu_dereference_check(*owner_storage(smap, owner), bpf_rcu_lock_held()); - if (!local_storage || hlist_empty(&local_storage->list)) { + if (!local_storage) { /* Very first elem for the owner */ err = check_flags(NULL, map_flags); if (err) @@ -698,17 +702,6 @@ bpf_local_storage_update(void *owner, struct bpf_local_storage_map *smap, if (err) return ERR_PTR(err); - /* Recheck local_storage->list under local_storage->lock */ - if (unlikely(hlist_empty(&local_storage->list))) { - /* A parallel del is happening and local_storage is going - * away. It has just been checked before, so very - * unlikely. Return instead of retry to keep things - * simple. - */ - err = -EAGAIN; - goto unlock; - } - old_sdata = bpf_local_storage_lookup(local_storage, smap, false); err = check_flags(old_sdata, map_flags); if (err) @@ -811,13 +804,16 @@ int bpf_local_storage_map_check_btf(const struct bpf_map *map, return 0; } -void bpf_local_storage_destroy(struct bpf_local_storage *local_storage) +/* + * Deferred looping local_storage->list to workqueue since sleeping may not be + * allowed in bpf_local_storage_destroy() + */ +static void bpf_local_storage_free_deferred(struct work_struct *work) { + struct bpf_local_storage *local_storage; struct bpf_local_storage_elem *selem; - bool free_storage = false; - HLIST_HEAD(free_selem_list); - struct hlist_node *n; - unsigned long flags; + + local_storage = container_of(work, struct bpf_local_storage, work); /* Neither the bpf_prog nor the bpf_map's syscall * could be modifying the local_storage->list now. @@ -828,33 +824,44 @@ void bpf_local_storage_destroy(struct bpf_local_storage *local_storage) * when unlinking elem from the local_storage->list and * the map's bucket->list. */ - raw_res_spin_lock_irqsave(&local_storage->lock, flags); - hlist_for_each_entry_safe(selem, n, &local_storage->list, snode) { - /* Always unlink from map before unlinking from - * local_storage. - */ - bpf_selem_unlink_map(selem); - /* If local_storage list has only one element, the - * bpf_selem_unlink_storage_nolock() will return true. - * Otherwise, it will return false. The current loop iteration - * intends to remove all local storage. So the last iteration - * of the loop will set the free_cgroup_storage to true. - */ - free_storage = bpf_selem_unlink_storage_nolock( - local_storage, selem, &free_selem_list); + rcu_read_lock(); +restart: + hlist_for_each_entry_rcu(selem, &local_storage->list, snode) { + bpf_selem_unlink_nofail(selem, NULL); + + if (need_resched()) { + cond_resched_rcu(); + goto restart; + } } - raw_res_spin_unlock_irqrestore(&local_storage->lock, flags); + rcu_read_unlock(); - bpf_selem_free_list(&free_selem_list, true); + bpf_local_storage_free(local_storage, false); +} + +/* + * Destroy local storage when the owner is going away. Caller must clear owner->storage + * and uncharge memory if memory charging is used. + * + * Since smaps associated with selems may already be gone, mem_uncharge() or + * owner_storage() cannot be called in this function. Let the owner (i.e., the caller) + * do it instead. + */ +u32 bpf_local_storage_destroy(struct bpf_local_storage *local_storage) +{ + INIT_WORK(&local_storage->work, bpf_local_storage_free_deferred); - if (free_storage) - bpf_local_storage_free(local_storage, true); + queue_work(system_dfl_wq, &local_storage->work); if (!refcount_dec_and_test(&local_storage->owner_refcnt)) { while (refcount_read(&local_storage->owner_refcnt)) cpu_relax(); smp_rmb(); /* pair with refcount_dec in bpf_selem_unlink_nofail */ } + + local_storage->owner = NULL; + + return sizeof(*local_storage) + local_storage->selems_size; } u64 bpf_local_storage_map_mem_usage(const struct bpf_map *map) @@ -948,11 +955,14 @@ void bpf_local_storage_map_free(struct bpf_map *map, rcu_read_lock(); /* No one is adding to b->list now */ - while ((selem = hlist_entry_safe( - rcu_dereference_raw(hlist_first_rcu(&b->list)), - struct bpf_local_storage_elem, map_node))) { - bpf_selem_unlink(selem, true); - cond_resched_rcu(); +restart: + hlist_for_each_entry_rcu(selem, &b->list, map_node) { + bpf_selem_unlink_nofail(selem, b); + + if (need_resched()) { + cond_resched_rcu(); + goto restart; + } } rcu_read_unlock(); } diff --git a/kernel/bpf/bpf_task_storage.c b/kernel/bpf/bpf_task_storage.c index 4d53aebe6784..ea7ea80d85e7 100644 --- a/kernel/bpf/bpf_task_storage.c +++ b/kernel/bpf/bpf_task_storage.c @@ -53,6 +53,7 @@ void bpf_task_storage_free(struct task_struct *task) if (!local_storage) goto out; + RCU_INIT_POINTER(task->bpf_storage, NULL); bpf_local_storage_destroy(local_storage); out: rcu_read_unlock(); @@ -134,7 +135,7 @@ static int task_storage_delete(struct task_struct *task, struct bpf_map *map) if (!sdata) return -ENOENT; - return bpf_selem_unlink(SELEM(sdata), false); + return bpf_selem_unlink(SELEM(sdata)); } static long bpf_pid_task_storage_delete_elem(struct bpf_map *map, void *key) diff --git a/net/core/bpf_sk_storage.c b/net/core/bpf_sk_storage.c index 7ec8a74e7ce5..abb0e8713a04 100644 --- a/net/core/bpf_sk_storage.c +++ b/net/core/bpf_sk_storage.c @@ -40,20 +40,25 @@ static int bpf_sk_storage_del(struct sock *sk, struct bpf_map *map) if (!sdata) return -ENOENT; - return bpf_selem_unlink(SELEM(sdata), false); + return bpf_selem_unlink(SELEM(sdata)); } /* Called by __sk_destruct() & bpf_sk_storage_clone() */ void bpf_sk_storage_free(struct sock *sk) { struct bpf_local_storage *sk_storage; + u32 uncharge; rcu_read_lock_dont_migrate(); sk_storage = rcu_dereference(sk->sk_bpf_storage); if (!sk_storage) goto out; - bpf_local_storage_destroy(sk_storage); + RCU_INIT_POINTER(sk->sk_bpf_storage, NULL); + + uncharge = bpf_local_storage_destroy(sk_storage); + if (uncharge) + atomic_sub(uncharge, &sk->sk_omem_alloc); out: rcu_read_unlock_migrate(); } -- 2.47.3