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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
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5
include/linux/sched.h
View file

@ -42,6 +42,7 @@ struct audit_context;
struct backing_dev_info;
struct bio_list;
struct blk_plug;
struct bpf_local_storage;
struct capture_control;
struct cfs_rq;
struct fs_struct;
@ -1348,6 +1349,10 @@ struct task_struct {
/* Used by LSM modules for access restriction: */
void *security;
#endif
#ifdef CONFIG_BPF_SYSCALL
/* Used by BPF task local storage */
struct bpf_local_storage __rcu *bpf_storage;
#endif
#ifdef CONFIG_GCC_PLUGIN_STACKLEAK
unsigned long lowest_stack;