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    SubjectRe: [PATCH v7 0/4] Add the ability to do BPF directed error injection
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    On 11/22/2017 10:23 PM, Josef Bacik wrote:
    > This is hopefully the final version, I've addressed the comment by Igno and
    > added his Acks.
    >
    > v6->v7:
    > - moved the opt-in macro to bpf.h out of kprobes.h.
    >
    > v5->v6:
    > - add BPF_ALLOW_ERROR_INJECTION() tagging for functions that will support this
    > feature. This way only functions that opt-in will be allowed to be
    > overridden.
    > - added a btrfs patch to allow error injection for open_ctree() so that the bpf
    > sample actually works.
    >
    > v4->v5:
    > - disallow kprobe_override programs from being put in the prog map array so we
    > don't tail call into something we didn't check. This allows us to make the
    > normal path still fast without a bunch of percpu operations.
    >
    > v3->v4:
    > - fix a build error found by kbuild test bot (I didn't wait long enough
    > apparently.)
    > - Added a warning message as per Daniels suggestion.
    >
    > v2->v3:
    > - added a ->kprobe_override flag to bpf_prog.
    > - added some sanity checks to disallow attaching bpf progs that have
    > ->kprobe_override set that aren't for ftrace kprobes.
    > - added the trace_kprobe_ftrace helper to check if the trace_event_call is a
    > ftrace kprobe.
    > - renamed bpf_kprobe_state to bpf_kprobe_override, fixed it so we only read this
    > value in the kprobe path, and thus only write to it if we're overriding or
    > clearing the override.
    >
    > 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.
    >
    > - Original message -
    >
    > 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,

    Ok, given the remaining feedback from Ingo was addressed and therefore
    the series acked, I've applied it to bpf-next tree, thanks Josef.

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