From mboxrd@z Thu Jan 1 00:00:00 1970 From: Alexei Starovoitov Subject: Re: [RFC PATCH bpf-next v2 4/4] error-injection: Support fault injection framework Date: Wed, 27 Dec 2017 19:49:28 -0800 Message-ID: <126a806d-e913-d243-6678-56fc3cff5e9e@fb.com> References: <151427438796.32561.4235654585430455286.stgit@devbox> <151427450538.32561.2776225740675148782.stgit@devbox> <20171227021255.sahkcpgyzohl5brs@ast-mbp> <20171227170910.5ac1074bc86341f194130119@kernel.org> <87e5e909-593d-7fd6-c7bb-714c1e3022a0@fb.com> <20171228103849.9be1a4507298b280b9df9c20@kernel.org> Mime-Version: 1.0 Content-Type: text/plain; charset="windows-1252"; format=flowed Content-Transfer-Encoding: 7bit Cc: Alexei Starovoitov , Josef Bacik , , , , , , , , , , , Josef Bacik , Akinobu Mita To: Masami Hiramatsu Return-path: In-Reply-To: <20171228103849.9be1a4507298b280b9df9c20@kernel.org> Sender: linux-kernel-owner@vger.kernel.org List-Id: netdev.vger.kernel.org On 12/27/17 5:38 PM, Masami Hiramatsu wrote: > On Wed, 27 Dec 2017 14:49:46 -0800 > Alexei Starovoitov wrote: > >> On 12/27/17 12:09 AM, Masami Hiramatsu wrote: >>> On Tue, 26 Dec 2017 18:12:56 -0800 >>> Alexei Starovoitov 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 >>>>> --- >>>>> 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. > > Sorry, I don't think so. > Even if it takes 16 bytes more for each points, I don't think it is > any overhead for machines in these days. Even if so, we can provide > a kconfig to reduce it. > I mean, we are living in GB-order memory are, and it will be bigger > in the future. Why we have to worry about hundreds of 16bytes memory > pieces? It will take a few KB, and even if we mark thousands of > functions, it never reaches 1MB, in GB memory pool. :) > > Of course, for many small-footprint embedded devices (like having > less than 128MB memory), this feature can be a overhead. But they > can cut off the table by kconfig. I still disagree on wasting 16-byte * num_of_funcs of .data here. The trade-off of usability vs memory just not worth it. Sorry. Please focus on testing your changes instead.