Messages in this thread | | | From | Song Liu <> | Subject | Re: [PATCH v2 bpf-next 2/4] bpf: introduce helper bpf_get_task_stak() | Date | Fri, 26 Jun 2020 22:37:38 +0000 |
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> On Jun 26, 2020, at 8:40 AM, Yonghong Song <yhs@fb.com> wrote: > > > > On 6/25/20 5:13 PM, Song Liu wrote: >> 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> >> [...] >> +++ b/include/uapi/linux/bpf.h >> @@ -3252,6 +3252,38 @@ union bpf_attr { >> * case of **BPF_CSUM_LEVEL_QUERY**, the current skb->csum_level >> * is returned or the error code -EACCES in case the skb is not >> * subject to CHECKSUM_UNNECESSARY. >> + * >> + * int bpf_get_task_stack(struct task_struct *task, void *buf, u32 size, u64 flags) > > Andrii's recent patch changed the return type to 'long' to align with > kernel u64 return type for better llvm code generation. > > Please rebase and you will see the new convention.
Will fix.
> >> + * Description >>
[...]
>> +static struct perf_callchain_entry * >> +get_callchain_entry_for_task(struct task_struct *task, u32 init_nr) >> +{ >> + struct perf_callchain_entry *entry; >> + int rctx; >> + >> + entry = get_callchain_entry(&rctx); >> + >> + if (rctx == -1) >> + return NULL; > > Is this needed? Should be below !entry enough?
It is needed before Peter's suggestion. After applying Peter's patch, this is no longer needed.
Thanks, Song
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