Re: [PATCH] error-injection: Add prompt for function error injection

Steven Rostedt
2022-12-02T23:17:35Z

On Fri, 2 Dec 2022 13:27:11 -0800
Alexei Starovoitov <alexei.starovoitov@gmail.com> wrote:

> --- a/lib/Kconfig.debug
> +++ b/lib/Kconfig.debug
> @@ -1874,8 +1874,12 @@ config NETDEV_NOTIFIER_ERROR_INJECT
> If unsure, say N.
>
> config FUNCTION_ERROR_INJECTION

Why not just call this "ERROR_INJECTION" having this be FUNCTION and the
one for functions be FUNC is confusing.

> + bool
> +
> +config FUNC_ERROR_INJECTION
> bool "Fault-injections of functions"
> depends on HAVE_FUNCTION_ERROR_INJECTION && KPROBES
> + select FUNCTION_ERROR_INJECTION
> help
> Add fault injections into various functions that are annotated with
> ALLOW_ERROR_INJECTION() in the kernel. BPF may also modify the return
> @@ -1883,6 +1887,17 @@ config FUNCTION_ERROR_INJECTION
>
> If unsure, say N
>
> +config SYSCALL_ERROR_INJECTION
> + bool "Error injections in syscalls"
> + depends on HAVE_FUNCTION_ERROR_INJECTION && KPROBES
> + select FUNCTION_ERROR_INJECTION
> + default y

IIUC, Linus prefers everything to be "default n" unless there's a really
good reason for it. Like only making other options available, but not doing
anything to the kernel. I do have DYNAMIC_FTRACE as "default y" but that's
only because it depends on CONFIG_FUNCTION_TRACER and nobody that enables
that should have DYNAMIC_FTRACE off (except for academia).

> + help
> + Allows error injection framework to return errors from syscalls.
> + BPF may modify return values of syscalls as well.

And here's the thing. If BPF returns anything *but* an error, then this is
a misnomer and incorrect. Name it something else like "HIJACK_SYSCALLS".

> +
> + If unsure, say Y

And I'm curious, why Y if unsure?

-- Steve

> +
> config FAULT_INJECTION
> bool "Fault-injection framework"
> depends on DEBUG_KERNEL
> diff --git a/lib/error-inject.c b/lib/error-inject.c
> index 1afca1b1cdea..9ba868eb8c43 100644
> --- a/lib/error-inject.c
> +++ b/lib/error-inject.c
> @@ -71,6 +71,10 @@ static void populate_error_injection_list(struct error_injection_entry *start,
>
> mutex_lock(&ei_mutex);
> for (iter = start; iter < end; iter++) {
> + if (iter->etype != EI_ETYPE_SYSCALL &&
> + !IS_ENABLED(CONFIG_FUNC_ERROR_INJECTION))
> + continue;
> +
> entry = (unsigned long)dereference_symbol_descriptor((void *)iter->addr);
>
> if (!kernel_text_address(entry) ||
> @@ -189,6 +193,8 @@ static const char *error_type_string(int etype)
> return "ERRNO_NULL";
> case EI_ETYPE_TRUE:
> return "TRUE";
> + case EI_ETYPE_SYSCALL:
> + return "SYSCALL";
> default:
> return "(unknown)";
> }