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bpf: Enable task local storage for tracing programs

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To access per-task data, BPF programs usually creates a hash table with
pid as the key. This is not ideal because:
 1. The user need to estimate the proper size of the hash table, which may
    be inaccurate;
 2. Big hash tables are slow;
 3. To clean up the data properly during task terminations, the user need
    to write extra logic.

Task local storage overcomes these issues and offers a better option for
these per-task data. Task local storage is only available to BPF_LSM. Now
enable it for tracing programs.

Unlike LSM programs, tracing programs can be called in IRQ contexts.
Helpers that access task local storage are updated to use
raw_spin_lock_irqsave() instead of raw_spin_lock_bh().

Tracing programs can attach to functions on the task free path, e.g.
exit_creds(). To avoid allocating task local storage after
bpf_task_storage_free(). bpf_task_storage_get() is updated to not allocate
new storage when the task is not refcounted (task->usage == 0).

Signed-off-by: Song Liu <songliubraving@fb.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: KP Singh <kpsingh@kernel.org>
Acked-by: Martin KaFai Lau <kafai@fb.com>
Link: https://lore.kernel.org/bpf/20210225234319.336131-2-songliubraving@fb.com
This commit is contained in:
Song Liu 2021-02-25 15:43:14 -08:00 • committed by Alexei Starovoitov
parent 9c8f21e6f8
commit a10787e6d5
10 changed files with 51 additions and 72 deletions
Download patch file Download diff file Expand all files Collapse all files

43
kernel/bpf/bpf_task_storage.c
View file

@ -15,7 +15,6 @@
#include <linux/bpf_local_storage.h>
#include <linux/filter.h>
#include <uapi/linux/btf.h>
#include <linux/bpf_lsm.h>
#include <linux/btf_ids.h>
#include <linux/fdtable.h>
@ -24,12 +23,8 @@ DEFINE_BPF_STORAGE_CACHE(task_cache);
static struct bpf_local_storage __rcu **task_storage_ptr(void *owner)
{
struct task_struct *task = owner;
struct bpf_storage_blob *bsb;
bsb = bpf_task(task);
if (!bsb)
return NULL;
return &bsb->storage;
return &task->bpf_storage;
}
static struct bpf_local_storage_data *
@ -38,13 +33,8 @@ task_storage_lookup(struct task_struct *task, struct bpf_map *map,
{
struct bpf_local_storage *task_storage;
struct bpf_local_storage_map *smap;
struct bpf_storage_blob *bsb;
bsb = bpf_task(task);
if (!bsb)
return NULL;
task_storage = rcu_dereference(bsb->storage);
task_storage = rcu_dereference(task->bpf_storage);
if (!task_storage)
return NULL;
@ -57,16 +47,12 @@ void bpf_task_storage_free(struct task_struct *task)
struct bpf_local_storage_elem *selem;
struct bpf_local_storage *local_storage;
bool free_task_storage = false;
struct bpf_storage_blob *bsb;
struct hlist_node *n;
bsb = bpf_task(task);
if (!bsb)
return;
unsigned long flags;
rcu_read_lock();
local_storage = rcu_dereference(bsb->storage);
local_storage = rcu_dereference(task->bpf_storage);
if (!local_storage) {
rcu_read_unlock();
return;
@ -81,7 +67,7 @@ void bpf_task_storage_free(struct task_struct *task)
* when unlinking elem from the local_storage->list and
* the map's bucket->list.
*/
raw_spin_lock_bh(&local_storage->lock);
raw_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.
@ -90,7 +76,7 @@ void bpf_task_storage_free(struct task_struct *task)
free_task_storage = bpf_selem_unlink_storage_nolock(
local_storage, selem, false);
}
raw_spin_unlock_bh(&local_storage->lock);
raw_spin_unlock_irqrestore(&local_storage->lock, flags);
rcu_read_unlock();
/* free_task_storage should always be true as long as
@ -150,7 +136,7 @@ static int bpf_pid_task_storage_update_elem(struct bpf_map *map, void *key,
*/
WARN_ON_ONCE(!rcu_read_lock_held());
task = pid_task(pid, PIDTYPE_PID);
if (!task || !task_storage_ptr(task)) {
if (!task) {
err = -ENOENT;
goto out;
}
@ -213,23 +199,16 @@ BPF_CALL_4(bpf_task_storage_get, struct bpf_map *, map, struct task_struct *,
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 || !task_storage_ptr(task))
if (!task)
return (unsigned long)NULL;
sdata = task_storage_lookup(task, map, true);
if (sdata)
return (unsigned long)sdata->data;
/* This helper must only be called from places where the lifetime of the task
* is guaranteed. Either by being refcounted or by being protected
* by an RCU read-side critical section.
*/
if (flags & BPF_LOCAL_STORAGE_GET_F_CREATE) {
/* only allocate new storage, when the task is refcounted */
if (refcount_read(&task->usage) &&
(flags & BPF_LOCAL_STORAGE_GET_F_CREATE)) {
sdata = bpf_local_storage_update(
task, (struct bpf_local_storage_map *)map, value,
BPF_NOEXIST);