Re: [PATCH v6 bpf-next 09/10] bpf: wire up sleepable bpf_get_stack() and bpf_get_task_stack() helpers

[Eduard Zingerman <eddyz87@gmail.com>]

On Wed, 2024-08-14 at 11:54 -0700, Andrii Nakryiko wrote:
> Add sleepable implementations of bpf_get_stack() and
> bpf_get_task_stack() helpers and allow them to be used from sleepable
> BPF program (e.g., sleepable uprobes).
> 
> Note, the stack trace IPs capturing itself is not sleepable (that would
> need to be a separate project), only build ID fetching is sleepable and
> thus more reliable, as it will wait for data to be paged in, if
> necessary. For that we make use of sleepable build_id_parse()
> implementation.
> 
> Now that build ID related internals in kernel/bpf/stackmap.c can be used
> both in sleepable and non-sleepable contexts, we need to add additional
> rcu_read_lock()/rcu_read_unlock() protection around fetching
> perf_callchain_entry, but with the refactoring in previous commit it's
> now pretty straightforward. We make sure to do rcu_read_unlock (in
> sleepable mode only) right before stack_map_get_build_id_offset() call
> which can sleep. By that time we don't have any more use of
> perf_callchain_entry.
> 
> Note, bpf_get_task_stack() will fail for user mode if task != current.
> And for kernel mode build ID are irrelevant. So in that sense adding
> sleepable bpf_get_task_stack() implementation is a no-op. It feel right
> to wire this up for symmetry and completeness, but I'm open to just
> dropping it until we support `user && crosstask` condition.
> 
> Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
> ---

All seems logical.
You skip wiring up support for sleepable bpf_get_task_stack() in
tp_prog_func_proto(), pe_prog_func_proto() and
raw_tp_prog_func_proto(), this is because these are used for programs
that are never run in sleepable context, right?

Reviewed-by: Eduard Zingerman <eddyz87@gmail.com>

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