From: Miroslav Benes <mbenes@suse.cz>
To: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Jessica Yu <jeyu@redhat.com>, Jiri Kosina <jikos@kernel.org>,
Petr Mladek <pmladek@suse.com>,
linux-kernel@vger.kernel.org, live-patching@vger.kernel.org,
Michael Ellerman <mpe@ellerman.id.au>,
Heiko Carstens <heiko.carstens@de.ibm.com>,
x86@kernel.org, linuxppc-dev@lists.ozlabs.org,
linux-s390@vger.kernel.org, Vojtech Pavlik <vojtech@suse.com>,
Jiri Slaby <jslaby@suse.cz>,
Chris J Arges <chris.j.arges@canonical.com>,
Andy Lutomirski <luto@kernel.org>, Ingo Molnar <mingo@kernel.org>,
Peter Zijlstra <peterz@infradead.org>,
Kamalesh Babulal <kamalesh@linux.vnet.ibm.com>,
Balbir Singh <bsingharora@gmail.com>
Subject: Re: [PATCH v4 15/15] livepatch: allow removal of a disabled patch
Date: Fri, 3 Feb 2017 17:48:52 +0100 (CET) [thread overview]
Message-ID: <alpine.LSU.2.20.1702031748010.28531@pobox.suse.cz> (raw)
In-Reply-To: <7b540d5a66243628eae1925e8871dc9678305973.1484839971.git.jpoimboe@redhat.com>
On Thu, 19 Jan 2017, Josh Poimboeuf wrote:
> From: Miroslav Benes <mbenes@suse.cz>
>
> Currently we do not allow patch module to unload since there is no
> method to determine if a task is still running in the patched code.
>
> The consistency model gives us the way because when the unpatching
> finishes we know that all tasks were marked as safe to call an original
> function. Thus every new call to the function calls the original code
> and at the same time no task can be somewhere in the patched code,
> because it had to leave that code to be marked as safe.
>
> We can safely let the patch module go after that.
>
> Completion is used for synchronization between module removal and sysfs
> infrastructure in a similar way to commit 942e443127e9 ("module: Fix
> mod->mkobj.kobj potentially freed too early").
>
> Note that we still do not allow the removal for immediate model, that is
> no consistency model. The module refcount may increase in this case if
> somebody disables and enables the patch several times. This should not
> cause any harm.
>
> With this change a call to try_module_get() is moved to
> __klp_enable_patch from klp_register_patch to make module reference
> counting symmetric (module_put() is in a patch disable path) and to
> allow to take a new reference to a disabled module when being enabled.
>
> Finally, we need to be very careful about possible races between
> klp_unregister_patch(), kobject_put() functions and operations
> on the related sysfs files.
>
> kobject_put(&patch->kobj) must be called without klp_mutex. Otherwise,
> it might be blocked by enabled_store() that needs the mutex as well.
> In addition, enabled_store() must check if the patch was not
> unregisted in the meantime.
>
> There is no need to do the same for other kobject_put() callsites
> at the moment. Their sysfs operations neiter take the lock nor
s/neiter/neither/
Thanks,
Miroslav
next prev parent reply other threads:[~2017-02-03 16:48 UTC|newest]
Thread overview: 44+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-01-19 15:46 [PATCH v4 00/15] livepatch: hybrid consistency model Josh Poimboeuf
2017-01-19 15:46 ` [PATCH v4 01/15] stacktrace/x86: add function for detecting reliable stack traces Josh Poimboeuf
2017-01-26 13:56 ` Petr Mladek
2017-01-26 17:57 ` Josh Poimboeuf
2017-01-27 8:47 ` Miroslav Benes
2017-01-27 17:13 ` Josh Poimboeuf
2017-02-01 19:57 ` [PATCH v4.1 " Josh Poimboeuf
2017-02-02 14:39 ` Miroslav Benes
2017-01-19 15:46 ` [PATCH v4 02/15] x86/entry: define _TIF_ALLWORK_MASK flags explicitly Josh Poimboeuf
2017-01-19 15:46 ` [PATCH v4 03/15] livepatch: create temporary klp_update_patch_state() stub Josh Poimboeuf
2017-01-27 8:52 ` Miroslav Benes
2017-01-19 15:46 ` [PATCH v4 04/15] livepatch/x86: add TIF_PATCH_PENDING thread flag Josh Poimboeuf
2017-01-19 15:46 ` [PATCH v4 05/15] livepatch/powerpc: " Josh Poimboeuf
2017-01-19 15:46 ` [PATCH v4 06/15] livepatch/s390: reorganize TIF thread flag bits Josh Poimboeuf
2017-01-19 15:46 ` [PATCH v4 07/15] livepatch/s390: add TIF_PATCH_PENDING thread flag Josh Poimboeuf
2017-01-19 15:46 ` [PATCH v4 08/15] livepatch: separate enabled and patched states Josh Poimboeuf
2017-01-19 15:46 ` [PATCH v4 09/15] livepatch: remove unnecessary object loaded check Josh Poimboeuf
2017-01-19 15:46 ` [PATCH v4 10/15] livepatch: move patching functions into patch.c Josh Poimboeuf
2017-01-19 15:46 ` [PATCH v4 11/15] livepatch: use kstrtobool() in enabled_store() Josh Poimboeuf
2017-01-19 15:46 ` [PATCH v4 12/15] livepatch: store function sizes Josh Poimboeuf
2017-01-19 15:46 ` [PATCH v4 13/15] livepatch: change to a per-task consistency model Josh Poimboeuf
2017-02-02 11:45 ` Petr Mladek
2017-02-02 11:47 ` Petr Mladek
2017-02-02 11:51 ` Petr Mladek
2017-02-03 16:21 ` Miroslav Benes
2017-02-03 20:39 ` Josh Poimboeuf
2017-02-06 16:44 ` Petr Mladek
2017-02-06 19:51 ` Josh Poimboeuf
2017-02-08 15:47 ` Petr Mladek
2017-02-08 16:46 ` Josh Poimboeuf
2017-02-09 10:24 ` Petr Mladek
2017-02-03 16:41 ` Miroslav Benes
2017-02-06 15:58 ` Josh Poimboeuf
2017-02-07 8:21 ` Miroslav Benes
2017-01-19 15:46 ` [PATCH v4 14/15] livepatch: add /proc/<pid>/patch_state Josh Poimboeuf
2017-01-31 14:31 ` Miroslav Benes
2017-01-31 14:56 ` Josh Poimboeuf
2017-02-01 8:54 ` Miroslav Benes
2017-01-19 15:46 ` [PATCH v4 15/15] livepatch: allow removal of a disabled patch Josh Poimboeuf
2017-02-03 16:48 ` Miroslav Benes [this message]
2017-02-01 20:02 ` [PATCH v4 00/15] livepatch: hybrid consistency model Josh Poimboeuf
2017-02-01 20:52 ` Miroslav Benes
2017-02-01 21:01 ` Jiri Kosina
2017-02-02 14:37 ` Petr Mladek
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