Re: [RFC 0/1] BPF tracing for arm64 using fprobe

[Mark Rutland]

Hi Alexei,

On Thu, Nov 17, 2022 at 08:50:12AM -0800, Alexei Starovoitov wrote:
> There might not be a task available where bpf trampoline is running.

I'm not sure what you mean by "there might not be a task available"; do you
mean that there might not be space in the per-task shadow stack, or that the
BPF program can be invoked inan IRQ context?

> rcu protection might not be there either.

We've spent a lot of time reworking entry/idle sequences with noinstr, so any
time BPF can be invoked, we should have a regular kernel environment available,
with RCU watching (but not necessarily in an RCU read-side critical section).
If BPF is being invoked without RCU watching, that is a bug that needs to be
fixed.

Do you have a specific example in mind?

Thanks,
Mark.