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From: Miroslav Benes <mbenes@suse.cz>
To: Petr Mladek <pmladek@suse.com>
Cc: Jiri Kosina <jikos@kernel.org>,
	Josh Poimboeuf <jpoimboe@redhat.com>,
	Jason Baron <jbaron@akamai.com>,
	Joe Lawrence <joe.lawrence@redhat.com>,
	Evgenii Shatokhin <eshatokhin@virtuozzo.com>,
	live-patching@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH v15 05/11] livepatch: Simplify API by removing registration step
Date: Thu, 10 Jan 2019 13:32:35 +0100 (CET)	[thread overview]
Message-ID: <alpine.LSU.2.21.1901101332150.15065@pobox.suse.cz> (raw)
In-Reply-To: <20190109124329.21991-6-pmladek@suse.com>

On Wed, 9 Jan 2019, Petr Mladek wrote:

> The possibility to re-enable a registered patch was useful for immediate
> patches where the livepatch module had to stay until the system reboot.
> The improved consistency model allows to achieve the same result by
> unloading and loading the livepatch module again.
> 
> Also we are going to add a feature called atomic replace. It will allow
> to create a patch that would replace all already registered patches.
> The aim is to handle dependent patches more securely. It will obsolete
> the stack of patches that helped to handle the dependencies so far.
> Then it might be unclear when a cumulative patch re-enabling is safe.
> 
> It would be complicated to support the many modes. Instead we could
> actually make the API and code easier to understand.
> 
> Therefore, remove the two step public API. All the checks and init calls
> are moved from klp_register_patch() to klp_enabled_patch(). Also the patch
> is automatically freed, including the sysfs interface when the transition
> to the disabled state is completed.
> 
> As a result, there is never a disabled patch on the top of the stack.
> Therefore we do not need to check the stack in __klp_enable_patch().
> And we could simplify the check in __klp_disable_patch().
> 
> Also the API and logic is much easier. It is enough to call
> klp_enable_patch() in module_init() call. The patch can be disabled
> by writing '0' into /sys/kernel/livepatch/<patch>/enabled. Then the module
> can be removed once the transition finishes and sysfs interface is freed.
> 
> The only problem is how to free the structures and kobjects safely.
> The operation is triggered from the sysfs interface. We could not put
> the related kobject from there because it would cause lock inversion
> between klp_mutex and kernfs locks, see kn->count lockdep map.
> 
> Therefore, offload the free task to a workqueue. It is perfectly fine:
> 
>   + The patch can no longer be used in the livepatch operations.
> 
>   + The module could not be removed until the free operation finishes
>     and module_put() is called.
> 
>   + The operation is asynchronous already when the first
>     klp_try_complete_transition() fails and another call
>     is queued with a delay.
> 
> Suggested-by: Josh Poimboeuf <jpoimboe@redhat.com>
> Signed-off-by: Petr Mladek <pmladek@suse.com>

Acked-by: Miroslav Benes <mbenes@suse.cz>

Miroslav

  reply	other threads:[~2019-01-10 12:32 UTC|newest]

Thread overview: 20+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-01-09 12:43 [PATCH v15 00/11] livepatch: Atomic replace feature Petr Mladek
2019-01-09 12:43 ` [PATCH v15 01/11] livepatch: Change unsigned long old_addr -> void *old_func in struct klp_func Petr Mladek
2019-01-09 12:43 ` [PATCH v15 02/11] livepatch: Shuffle klp_enable_patch()/klp_disable_patch() code Petr Mladek
2019-01-09 12:43 ` [PATCH v15 03/11] livepatch: Consolidate klp_free functions Petr Mladek
2019-01-09 14:35   ` Miroslav Benes
2019-01-09 12:43 ` [PATCH v15 04/11] livepatch: Don't block the removal of patches loaded after a forced transition Petr Mladek
2019-01-09 14:50   ` Miroslav Benes
2019-01-09 12:43 ` [PATCH v15 05/11] livepatch: Simplify API by removing registration step Petr Mladek
2019-01-10 12:32   ` Miroslav Benes [this message]
2019-01-09 12:43 ` [PATCH v15 06/11] livepatch: Use lists to manage patches, objects and functions Petr Mladek
2019-01-09 12:43 ` [PATCH v15 07/11] livepatch: Add atomic replace Petr Mladek
2019-01-10 13:05   ` Miroslav Benes
2019-01-09 12:43 ` [PATCH v15 08/11] livepatch: Remove Nop structures when unused Petr Mladek
2019-01-10 13:42   ` Miroslav Benes
2019-01-09 12:43 ` [PATCH v15 09/11] livepatch: Atomic replace and cumulative patches documentation Petr Mladek
2019-01-09 12:43 ` [PATCH v15 10/11] livepatch: Remove ordering (stacking) of the livepatches Petr Mladek
2019-01-10 13:56   ` Miroslav Benes
2019-01-09 12:43 ` [PATCH v15 11/11] selftests/livepatch: introduce tests Petr Mladek
2019-01-11 17:44 ` [PATCH v15 00/11] livepatch: Atomic replace feature Josh Poimboeuf
2019-01-11 19:56 ` Jiri Kosina

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