Re: [RFC PATCH bpf-next v2 4/4] error-injection: Support fault injection framework

[Alexei Starovoitov]

On 12/27/17 12:09 AM, Masami Hiramatsu wrote:
> On Tue, 26 Dec 2017 18:12:56 -0800
> Alexei Starovoitov <alexei.starovoitov@xxxxxxxxx> wrote:
>
> > On Tue, Dec 26, 2017 at 04:48:25PM +0900, Masami Hiramatsu wrote:
> > > Support in-kernel fault-injection framework via debugfs.
> > > This allows you to inject a conditional error to specified
> > > function using debugfs interfaces.
> > >
> > > Signed-off-by: Masami Hiramatsu <mhiramat@xxxxxxxxxx>
> > > ---
> > >  Documentation/fault-injection/fault-injection.txt |    5 +
> > >  kernel/Makefile                                   |    1
> > >  kernel/fail_function.c                            |  169 +++++++++++++++++++++
> > >  lib/Kconfig.debug                                 |   10 +
> > >  4 files changed, 185 insertions(+)
> > >  create mode 100644 kernel/fail_function.c
> > >
> > > diff --git a/Documentation/fault-injection/fault-injection.txt b/Documentation/fault-injection/fault-injection.txt
> > > index 918972babcd8..6243a588dd71 100644
> > > --- a/Documentation/fault-injection/fault-injection.txt
> > > +++ b/Documentation/fault-injection/fault-injection.txt
> > > @@ -30,6 +30,11 @@ o fail_mmc_request
> > >    injects MMC data errors on devices permitted by setting
> > >    debugfs entries under /sys/kernel/debug/mmc0/fail_mmc_request
> > >
> > > +o fail_function
> > > +
> > > +  injects error return on specific functions by setting debugfs entries
> > > +  under /sys/kernel/debug/fail_function. No boot option supported.
> >
> > I like it.
> > Could you document it a bit better?
>
> Yes, I will do in next series.
>
> > In particular retval is configurable, but without an example no one
> > will be able to figure out how to use it.
>
> Ah, right. BTW, as I pointed in the covermail, should we store the
> expected error value range into the injectable list? e.g.
>
> ALLOW_ERROR_INJECTION(open_ctree, -1, -MAX_ERRNO)
>
> And provide APIs to check/get it.

I'm afraid such check would be too costly.
Right now we have only two functions marked but I expect hundreds more
will be added in the near future as soon as developers realize the
potential of such error injection.
All of ALLOW_ERROR_INJECTION marks add 8 byte overhead each to .data.
Multiple by 1k and we have 8k of data spent on marks.
If we add max/min range marks that doubles it for very little use.
I think marking function only is enough.