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Wed, 4 Nov 2020 22:08:21 +0000 Date: Wed, 4 Nov 2020 14:08:14 -0800 From: Martin KaFai Lau CC: , , Song Liu , Alexei Starovoitov , Daniel Borkmann , Paul Turner , Jann Horn , Hao Luo Subject: Re: [PATCH bpf-next v3 1/9] bpf: Implement task local storage Message-ID: <20201104220814.quq7jzpeb4wcyffv@kafai-mbp.dhcp.thefacebook.com> 0;95;0cTo: KP Singh References: <20201104164453.74390-1-kpsingh@chromium.org> <20201104164453.74390-2-kpsingh@chromium.org> Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20201104164453.74390-2-kpsingh@chromium.org> X-Originating-IP: [2620:10d:c090:400::5:3041] X-ClientProxiedBy: MW3PR05CA0028.namprd05.prod.outlook.com (2603:10b6:303:2b::33) To BY5PR15MB3571.namprd15.prod.outlook.com (2603:10b6:a03:1f6::32) MIME-Version: 1.0 X-MS-Exchange-MessageSentRepresentingType: 1 Received: from kafai-mbp.dhcp.thefacebook.com (2620:10d:c090:400::5:3041) by MW3PR05CA0028.namprd05.prod.outlook.com (2603:10b6:303:2b::33) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.3541.10 via Frontend Transport; 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(no To-header on input) Precedence: bulk List-ID: X-Mailing-List: bpf@vger.kernel.org On Wed, Nov 04, 2020 at 05:44:45PM +0100, KP Singh wrote: [ ... ] > +static void *bpf_pid_task_storage_lookup_elem(struct bpf_map *map, void *key) > +{ > + struct bpf_local_storage_data *sdata; > + struct task_struct *task; > + unsigned int f_flags; > + struct pid *pid; > + int fd, err; > + > + fd = *(int *)key; > + pid = pidfd_get_pid(fd, &f_flags); > + if (IS_ERR(pid)) > + return ERR_CAST(pid); > + > + /* We should be in an RCU read side critical section, it should be safe > + * to call pid_task. > + */ > + WARN_ON_ONCE(!rcu_read_lock_held()); > + task = pid_task(pid, PIDTYPE_PID); > + if (!task) { > + err = -ENOENT; > + goto out; > + } > + > + sdata = task_storage_lookup(task, map, true); > + put_pid(pid); > + return sdata ? sdata->data : NULL; > +out: > + put_pid(pid); > + return ERR_PTR(err); > +} > + > +static int bpf_pid_task_storage_update_elem(struct bpf_map *map, void *key, > + void *value, u64 map_flags) > +{ > + struct bpf_local_storage_data *sdata; > + struct task_struct *task; > + unsigned int f_flags; > + struct pid *pid; > + int fd, err; > + > + fd = *(int *)key; > + pid = pidfd_get_pid(fd, &f_flags); > + if (IS_ERR(pid)) > + return PTR_ERR(pid); > + > + /* We should be in an RCU read side critical section, it should be safe > + * to call pid_task. > + */ > + WARN_ON_ONCE(!rcu_read_lock_held()); > + task = pid_task(pid, PIDTYPE_PID); > + if (!task) { > + err = -ENOENT; > + goto out; > + } > + > + sdata = bpf_local_storage_update( > + task, (struct bpf_local_storage_map *)map, value, map_flags); It seems the task is protected by rcu here and the task may be going away. Is it ok? or the following comment in the later "BPF_CALL_4(bpf_task_storage_get, ...)" is no longer valid? /* This helper must only called from where the task is guaranteed * to have a refcount and cannot be freed. */ > + > + err = PTR_ERR_OR_ZERO(sdata); > +out: > + put_pid(pid); > + return err; > +} > + [ ... ] > +BPF_CALL_4(bpf_task_storage_get, struct bpf_map *, map, struct task_struct *, > + task, void *, value, u64, flags) > +{ > + struct bpf_local_storage_data *sdata; > + > + if (flags & ~(BPF_LOCAL_STORAGE_GET_F_CREATE)) > + return (unsigned long)NULL; > + > + /* explicitly check that the task_storage_ptr is not > + * NULL as task_storage_lookup returns NULL in this case and > + * bpf_local_storage_update expects the owner to have a > + * valid storage pointer. > + */ > + if (!task_storage_ptr(task)) > + return (unsigned long)NULL; > + > + sdata = task_storage_lookup(task, map, true); > + if (sdata) > + return (unsigned long)sdata->data; > + > + /* This helper must only called from where the task is guaranteed > + * to have a refcount and cannot be freed. > + */ > + if (flags & BPF_LOCAL_STORAGE_GET_F_CREATE) { > + sdata = bpf_local_storage_update( > + task, (struct bpf_local_storage_map *)map, value, > + BPF_NOEXIST); > + return IS_ERR(sdata) ? (unsigned long)NULL : > + (unsigned long)sdata->data; > + } > + > + return (unsigned long)NULL; > +} > + [ ... ] > diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c > index 8f50c9c19f1b..f3fe9f53f93c 100644 > --- a/kernel/bpf/syscall.c > +++ b/kernel/bpf/syscall.c > @@ -773,7 +773,8 @@ static int map_check_btf(struct bpf_map *map, const struct btf *btf, > map->map_type != BPF_MAP_TYPE_ARRAY && > map->map_type != BPF_MAP_TYPE_CGROUP_STORAGE && > map->map_type != BPF_MAP_TYPE_SK_STORAGE && > - map->map_type != BPF_MAP_TYPE_INODE_STORAGE) > + map->map_type != BPF_MAP_TYPE_INODE_STORAGE && > + map->map_type != BPF_MAP_TYPE_TASK_STORAGE) This is to enable spin lock support in a map's value. Without peeking patch 5, I was confused a bit here. It seems patch 5 was missed when inode storage was added. > return -ENOTSUPP; > if (map->spin_lock_off + sizeof(struct bpf_spin_lock) > > map->value_size) {