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Date: Wed, 01 Nov 2017 10:55:02 +0900 (KST)
Message-Id: <20171101.105502.2238912905275925246.davem@davemloft.net>
To: josef@toxicpanda.com
Cc: netdev@vger.kernel.org, linux-kernel@vger.kernel.org, ast@kernel.org,
        kernel-team@fb.com
Subject: Re: [PATCH 0/2][v2] Add the ability to do BPF directed error
 injection
From: David Miller <davem@davemloft.net>
In-Reply-To: <1509464757-2222-1-git-send-email-josef@toxicpanda.com>
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From: Josef Bacik <josef@toxicpanda.com>
Date: Tue, 31 Oct 2017 11:45:55 -0400

> v1->v2:
> - moved things around to make sure that bpf_override_return could really only be
>   used for an ftrace kprobe.
> - killed the special return values from trace_call_bpf.
> - renamed pc_modified to bpf_kprobe_state so bpf_override_return could tell if
>   it was being called from an ftrace kprobe context.
> - reworked the logic in kprobe_perf_func to take advantage of bpf_kprobe_state.
> - updated the test as per Alexei's review.
> 
> A lot of our error paths are not well tested because we have no good way of
> injecting errors generically.  Some subystems (block, memory) have ways to
> inject errors, but they are random so it's hard to get reproduceable results.
> 
> With BPF we can add determinism to our error injection.  We can use kprobes and
> other things to verify we are injecting errors at the exact case we are trying
> to test.  This patch gives us the tool to actual do the error injection part.
> It is very simple, we just set the return value of the pt_regs we're given to
> whatever we provide, and then override the PC with a dummy function that simply
> returns.
> 
> Right now this only works on x86, but it would be simple enough to expand to
> other architectures.  Thanks,

This appears to moreso target the tracing tree than the networking tree.

Let me know if that's not the case and I should be the one intergrating
these changes.

Thanks.