From: Libor Pechacek <lpechacek@suse.cz>
To: Joe Lawrence <joe.lawrence@redhat.com>
Cc: Petr Mladek <pmladek@suse.com>, Miroslav Benes <mbenes@suse.cz>,
linux-kernel@vger.kernel.org, live-patching@vger.kernel.org,
linux-kbuild@vger.kernel.org
Subject: Re: [PATCH v4 00/10] klp-convert livepatch build tooling
Date: Fri, 14 Jun 2019 18:36:55 +0200 [thread overview]
Message-ID: <20190614163655.GC15002@fm.suse.cz> (raw)
In-Reply-To: <a0db1cee-8bba-4093-c3ca-4c2fe61b15ba@redhat.com>
On Fri 14-06-19 10:20:09, Joe Lawrence wrote:
> On 6/14/19 4:34 AM, Petr Mladek wrote:
[...]
> > Anyway, I am curious about one thing. I saw:
> >
> > function __load_mod() {
> > local mod="$1"; shift
> >
> > local msg="% modprobe $mod $*"
> > log "${msg%% }"
> > ret=$(modprobe "$mod" "$@" 2>&1)
> > if [[ "$ret" != "" ]]; then
> > die "$ret"
> > fi
> >
> > # Wait for module in sysfs ...
> > loop_until '[[ -e "/sys/module/$mod" ]]' ||
> > die "failed to load module $mod"
> > }
> >
> > Is the waiting for sysfs really necessary here?
> >
> > Note that it is /sys/module and not /sys/kernel/livepatch/.
>
> I can't remember if that was just paranoid-protective-bash coding or
> actually required. Libor provided great feedback on the initial patch
> series that introduced the self-tests, perhaps he remembers.
I don't recall analyzing this spot in detail but looking at it now I don't see
anything wrong with it. While the check is likely superfluous, I'm not against
keeping it in place.
> > My understanding is that modprobe waits until the module succesfully
> > loaded. mod_sysfs_setup() is called before the module init callback.
> > Therefore the sysfs interface should be read before modprobe returns.
> > Do I miss something?
> >
> > If it works different way then there might be some races because
> > mod_sysfs_setup() is called before the module is alive.
>
> All of this is called from a single bash script function, so in a call stack
> fashion, something like this would occur when loading a livepatch module:
>
> [ mod_sysfs_setup() ]
> modprobe waits for: .init complete, MODULE_STATE_LIVE
> __load_mod() waits for: /sys/module/$mod
> load_lp_nowait() waits for: /sys/kernel/livepatch/$mod
> load_lp() waits for: /sys/kernel/livepatch/$mod/transition = 0
> test-script.sh
>
> So I would think that by calling modprobe, we ensure that the module code is
> ready to go. The /sys/module/$mod check might be redundant as you say, but
> because modprobe completed, we should be safe, no?
>
> The only "nowait" function we have is load_lp_nowait(), which would let us
> march onward before the livepatch transition may have completed.
And even that one is waiting for the live patch module name appear under
/sys/kernel/livepatch/. This is IMHO acceptable level of paranoia.
Libor
--
Libor Pechacek
SUSE Labs
next prev parent reply other threads:[~2019-06-14 16:37 UTC|newest]
Thread overview: 42+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-05-09 14:38 [PATCH v4 00/10] klp-convert livepatch build tooling Joe Lawrence
2019-05-09 14:38 ` [PATCH v4 01/10] livepatch: Create and include UAPI headers Joe Lawrence
2019-05-09 14:38 ` [PATCH v4 02/10] kbuild: Support for Symbols.list creation Joe Lawrence
2019-05-21 13:48 ` Masahiro Yamada
2019-05-09 14:38 ` [PATCH v4 03/10] livepatch: Add klp-convert tool Joe Lawrence
2019-07-31 2:50 ` Masahiro Yamada
2019-07-31 3:36 ` Masahiro Yamada
2019-08-09 18:42 ` Joe Lawrence
2019-08-13 1:15 ` Masahiro Yamada
2019-05-09 14:38 ` [PATCH v4 04/10] livepatch: Add klp-convert annotation helpers Joe Lawrence
2019-05-09 14:38 ` [PATCH v4 05/10] modpost: Integrate klp-convert Joe Lawrence
2019-05-09 14:38 ` [PATCH v4 06/10] modpost: Add modinfo flag to livepatch modules Joe Lawrence
2019-07-31 5:58 ` Masahiro Yamada
2019-08-12 15:56 ` Joe Lawrence
2019-08-15 15:05 ` Masahiro Yamada
2019-08-16 8:19 ` Miroslav Benes
2019-08-16 12:43 ` Joe Lawrence
2019-08-16 19:01 ` Joe Lawrence
2019-08-19 3:50 ` Masahiro Yamada
2019-08-19 15:55 ` Joe Lawrence
2019-08-20 7:54 ` Miroslav Benes
2019-08-19 3:49 ` Masahiro Yamada
2019-08-19 7:31 ` Miroslav Benes
2019-08-19 16:02 ` Joe Lawrence
2019-08-22 3:35 ` Masahiro Yamada
2019-08-13 10:26 ` Miroslav Benes
2019-05-09 14:38 ` [PATCH v4 07/10] livepatch: Add sample livepatch module Joe Lawrence
2019-08-16 11:35 ` Masahiro Yamada
2019-08-16 12:47 ` Joe Lawrence
2019-05-09 14:38 ` [PATCH v4 08/10] documentation: Update on livepatch elf format Joe Lawrence
2019-05-09 14:38 ` [PATCH v4 09/10] livepatch/selftests: add klp-convert Joe Lawrence
2019-05-09 14:38 ` [PATCH v4 10/10] livepatch/klp-convert: abort on special sections Joe Lawrence
2019-06-13 13:00 ` [PATCH v4 00/10] klp-convert livepatch build tooling Miroslav Benes
2019-06-13 13:15 ` Joe Lawrence
2019-06-13 20:48 ` Joe Lawrence
2019-06-14 8:34 ` Petr Mladek
2019-06-14 14:20 ` Joe Lawrence
2019-06-14 16:36 ` Libor Pechacek [this message]
2019-06-25 11:36 ` Miroslav Benes
2019-06-25 13:24 ` Joe Lawrence
2019-06-25 19:08 ` Joe Lawrence
2019-06-26 10:27 ` Miroslav Benes
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