linux-kernel - Re: [RFC PATCH v3 00/22] arm64: livepatch: Use ORC for dynamic frame pointer validation

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Message-ID: <ZADNdp5U+lP10Oqo@alley>
Date:   Thu, 2 Mar 2023 17:23:18 +0100
From:   Petr Mladek <pmladek@...e.com>
To:     "Tomohiro Misono (Fujitsu)" <misono.tomohiro@...itsu.com>
Cc:     "'madvenka@...ux.microsoft.com'" <madvenka@...ux.microsoft.com>,
        "jpoimboe@...hat.com" <jpoimboe@...hat.com>,
        "peterz@...radead.org" <peterz@...radead.org>,
        "chenzhongjin@...wei.com" <chenzhongjin@...wei.com>,
        "mark.rutland@....com" <mark.rutland@....com>,
        "broonie@...nel.org" <broonie@...nel.org>,
        "Keiya Nobuta (Fujitsu)" <nobuta.keiya@...itsu.com>,
        "sjitindarsingh@...il.com" <sjitindarsingh@...il.com>,
        "catalin.marinas@....com" <catalin.marinas@....com>,
        "will@...nel.org" <will@...nel.org>,
        "jamorris@...ux.microsoft.com" <jamorris@...ux.microsoft.com>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "live-patching@...r.kernel.org" <live-patching@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [RFC PATCH v3 00/22] arm64: livepatch: Use ORC for dynamic frame
 pointer validation

On Wed 2023-03-01 03:12:08, Tomohiro Misono (Fujitsu) wrote:
> <snip>
> > Testing
> > =======
> > 
> > - I have run all of the livepatch selftests successfully. I have written a
> >   couple of extra selftests myself which I will be posting separately
> Hi,
> 
> What test configuration/environment you are using for test?
> When I tried kselftest with fedora based config on VM, I got errors
> because livepatch transition won't finish until signal is sent
> (i.e. it takes 15s for every transition).
> 
> [excerpt from test result]
>   ```
>   $ sudo ./test-livepatch.sh
>   TEST: basic function patching ... not ok
>   
>   --- expected
>   +++ result
>   @@ -2,11 +2,13 @@
>    livepatch: enabling patch 'test_klp_livepatch'
>    livepatch: 'test_klp_livepatch': initializing patching transition
>    livepatch: 'test_klp_livepatch': starting patching transition
>   +livepatch: signaling remaining tasks
>    livepatch: 'test_klp_livepatch': completing patching transition
>   ```

It might be interesting to see what process is blocking the
transition. The transition state is visible in
/proc/<pid>/patch_state.

The transition is blocked when a process is in KLP_UNPATCHED state.
It is defined in include/linux/livepatch.h:

#define KLP_UNPATCHED	 0

Well, the timing against the transition is important. The following
might help to see the blocking processes:

$> modprobe livepatch-sample ; \
   sleep 1; \
   for proc_path in \
       `grep "\-1"  /proc/*/patch_state | cut -d '/'  -f-3` ; \
   do \
       cat $proc_path/comm ; \
       cat $proc_path/stack ; \
       echo ===  ; \
   done

After this the livepatch has to be manualy disabled and removed

$> echo 0 >/sys/kernel/livepatch/livepatch_sample/enabled
$> rmmod livepatch_sample

Best Regards,
Petr