linux-kernel - Re: [PATCH bpf-next v4 5/5] error-injection: Support fault injection framework

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Date:   Fri, 12 Jan 2018 01:15:52 +0900
From:   Masami Hiramatsu <mhiramat@...nel.org>
To:     Akinobu Mita <akinobu.mita@...il.com>
Cc:     mhiramat@...nel.org, Alexei Starovoitov <ast@...com>,
        Josef Bacik <jbacik@...com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Ingo Molnar <mingo@...hat.com>,
        "David S. Miller" <davem@...emloft.net>,
        netdev <netdev@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>, ast@...nel.org,
        kernel-team@...com, daniel@...earbox.net,
        linux-btrfs@...r.kernel.org, darrick.wong@...cle.com,
        Josef Bacik <josef@...icpanda.com>
Subject: Re: [PATCH bpf-next v4 5/5] error-injection: Support fault
 injection framework

On Thu, 11 Jan 2018 23:44:57 +0900
Akinobu Mita <akinobu.mita@...il.com> wrote:

> 2018-01-11 9:51 GMT+09:00 Masami Hiramatsu <mhiramat@...nel.org>:
> > Support in-kernel fault-injection framework via debugfs.
> > This allows you to inject a conditional error to specified
> > function using debugfs interfaces.
> >
> > Here is the result of test script described in
> > Documentation/fault-injection/fault-injection.txt
> >
> >   ===========
> >   # ./test_fail_function.sh
> >   1+0 records in
> >   1+0 records out
> >   1048576 bytes (1.0 MB, 1.0 MiB) copied, 0.0227404 s, 46.1 MB/s
> >   btrfs-progs v4.4
> >   See http://btrfs.wiki.kernel.org for more information.
> >
> >   Label:              (null)
> >   UUID:               bfa96010-12e9-4360-aed0-42eec7af5798
> >   Node size:          16384
> >   Sector size:        4096
> >   Filesystem size:    1001.00MiB
> >   Block group profiles:
> >     Data:             single            8.00MiB
> >     Metadata:         DUP              58.00MiB
> >     System:           DUP              12.00MiB
> >   SSD detected:       no
> >   Incompat features:  extref, skinny-metadata
> >   Number of devices:  1
> >   Devices:
> >      ID        SIZE  PATH
> >       1  1001.00MiB  /dev/loop2
> >
> >   mount: mount /dev/loop2 on /opt/tmpmnt failed: Cannot allocate memory
> >   SUCCESS!
> >   ===========
> >
> >
> > Signed-off-by: Masami Hiramatsu <mhiramat@...nel.org>
> > Reviewed-by: Josef Bacik <jbacik@...com>
> > ---
> >   Changes in v3:
> >    - Check and adjust error value for each target function
> >    - Clear kporbe flag for reuse
> >    - Add more documents and example
> > ---
> >  Documentation/fault-injection/fault-injection.txt |   62 ++++++
> >  kernel/Makefile                                   |    1
> >  kernel/fail_function.c                            |  217 +++++++++++++++++++++
> >  lib/Kconfig.debug                                 |   10 +
> >  4 files changed, 290 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..4aecbceef9d2 100644
> > --- a/Documentation/fault-injection/fault-injection.txt
> > +++ b/Documentation/fault-injection/fault-injection.txt
> > @@ -30,6 +30,12 @@ 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, which are marked by
> > +  ALLOW_ERROR_INJECTION() macro, by setting debugfs entries
> > +  under /sys/kernel/debug/fail_function. No boot option supported.
> > +
> >  Configure fault-injection capabilities behavior
> >  -----------------------------------------------
> >
> > @@ -123,6 +129,24 @@ configuration of fault-injection capabilities.
> >         default is 'N', setting it to 'Y' will disable failure injections
> >         when dealing with private (address space) futexes.
> >
> > +- /sys/kernel/debug/fail_function/inject:
> > +
> > +       specifies the target function of error injection by name.
> > +
> > +- /sys/kernel/debug/fail_function/retval:
> > +
> > +       specifies the "error" return value to inject to the given
> > +       function.
> > +
> 
> Is it possible to inject errors into multiple functions at the same time?

Yes, it is.

> If so, it will be more useful to support it in the fault injection, too.
> Because some kind of bugs are caused by the combination of errors.
> (e.g. another error in an error path)
> 
> I suggest the following interface.
> 
> - /sys/kernel/debug/fail_function/inject:
> 
>   specifies the target function of error injection by name.
>   /sys/kernel/debug/fail_function/<func>/ directory will be created.
> 
> - /sys/kernel/debug/fail_function/uninject:
> 
>   specifies the target function of error injection by name that is
>   currently being injected.  /sys/kernel/debug/fail_function/<func>/
>   directory will be removed.
> 
> - /sys/kernel/debug/fail_function/<func>/retval:
> 
>   specifies the "error" return value to inject to the given function.

OK, it is easy to make it. But also we might need to consider using bpf
if we do such complex error injection.

BTW, would we need "uninject" file? or just make inject file accept
"!function" syntax to remove function as ftrace does?

Thank you,

-- 
Masami Hiramatsu <mhiramat@...nel.org>