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bpf: Introduce helper bpf_get_task_stack()

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Introduce helper bpf_get_task_stack(), which dumps stack trace of given
task. This is different to bpf_get_stack(), which gets stack track of
current task. One potential use case of bpf_get_task_stack() is to call
it from bpf_iter__task and dump all /proc/<pid>/stack to a seq_file.

bpf_get_task_stack() uses stack_trace_save_tsk() instead of
get_perf_callchain() for kernel stack. The benefit of this choice is that
stack_trace_save_tsk() doesn't require changes in arch/. The downside of
using stack_trace_save_tsk() is that stack_trace_save_tsk() dumps the
stack trace to unsigned long array. For 32-bit systems, we need to
translate it to u64 array.

Signed-off-by: Song Liu <songliubraving@fb.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: Andrii Nakryiko <andriin@fb.com>
Link: https://lore.kernel.org/bpf/20200630062846.664389-3-songliubraving@fb.com
This commit is contained in:
Song Liu
2020-06-29 23:28:44 -07:00
committed by Alexei Starovoitov
parent d141b8bc57
commit fa28dcb82a
7 changed files with 153 additions and 7 deletions
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kernel/bpf/verifier.c
+3 -1
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@@ -4864,7 +4864,9 @@ static int check_helper_call(struct bpf_verifier_env *env, int func_id, int insn
if (err)
return err;
if (func_id == BPF_FUNC_get_stack && !env->prog->has_callchain_buf) {
if ((func_id == BPF_FUNC_get_stack ||
func_id == BPF_FUNC_get_task_stack) &&
!env->prog->has_callchain_buf) {
const char *err_str;
#ifdef CONFIG_PERF_EVENTS