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 08/11] livepatch: Remove Nop structures when unused
Date: Thu, 10 Jan 2019 14:42:17 +0100 (CET) [thread overview]
Message-ID: <alpine.LSU.2.21.1901101441580.15065@pobox.suse.cz> (raw)
In-Reply-To: <20190109124329.21991-9-pmladek@suse.com>
On Wed, 9 Jan 2019, Petr Mladek wrote:
> Replaced patches are removed from the stack when the transition is
> finished. It means that Nop structures will never be needed again
> and can be removed. Why should we care?
>
> + Nop structures give the impression that the function is patched
> even though the ftrace handler has no effect.
>
> + Ftrace handlers do not come for free. They cause slowdown that might
> be visible in some workloads. The ftrace-related slowdown might
> actually be the reason why the function is no longer patched in
> the new cumulative patch. One would expect that cumulative patch
> would help solve these problems as well.
>
> + Cumulative patches are supposed to replace any earlier version of
> the patch. The amount of NOPs depends on which version was replaced.
> This multiplies the amount of scenarios that might happen.
>
> One might say that NOPs are innocent. But there are even optimized
> NOP instructions for different processors, for example, see
> arch/x86/kernel/alternative.c. And klp_ftrace_handler() is much
> more complicated.
>
> + It sounds natural to clean up a mess that is no longer needed.
> It could only be worse if we do not do it.
>
> This patch allows to unpatch and free the dynamic structures independently
> when the transition finishes.
>
> The free part is a bit tricky because kobject free callbacks are called
> asynchronously. We could not wait for them easily. Fortunately, we do
> not have to. Any further access can be avoided by removing them from
> the dynamic lists.
>
> Signed-off-by: Petr Mladek <pmladek@suse.com>
Acked-by: Miroslav Benes <mbenes@suse.cz>
Miroslav
next prev parent reply other threads:[~2019-01-10 13:42 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
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 [this message]
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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