From: Petr Mladek <pmladek@suse.com>
To: Miroslav Benes <mbenes@suse.cz>
Cc: jpoimboe@redhat.com, jeyu@redhat.com, jikos@kernel.org,
corbet@lwn.net, live-patching@vger.kernel.org,
linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] Documentation/livepatch: remove the limitation for schedule() patching
Date: Fri, 6 Jan 2017 16:01:40 +0100 [thread overview]
Message-ID: <20170106150140.GX14894@pathway.suse.cz> (raw)
In-Reply-To: <20170106140045.26331-1-mbenes@suse.cz>
On Fri 2017-01-06 15:00:45, Miroslav Benes wrote:
> The Limitations section of the documentation describes the impossibility
> to livepatch anything that is inlined to __schedule() function. This had
> been true till 4.9 kernel came. Thanks to commit 0100301bfdf5
> ("sched/x86: Rewrite the switch_to() code") from Brian Gerst there is
> __switch_to_asm function now (implemented in assembly) called properly
> from context_switch(). RIP is thus saved on the stack and a task would
> return to proper version of __schedule() et al. functions.
>
> Of course __switch_to_asm() is not patchable for the reason described in
> the section. But there is no __fentry__ call and I cannot imagine a
> reason to do it anyway.
>
> Therefore, remove the paragraphs from the section.
>
> Signed-off-by: Miroslav Benes <mbenes@suse.cz>
It is great to get a feature for free ;-)
Reviewed-by: Petr Mladek <pmladek@suse.com>
Best Regards,
Petr
---
> FWIW, I also tested this to be sure on top of the consistency model
> patch set. I patched schedule() function which calls __schedule() (it is
> impossible to patch it directly due to notrace attribute). It works well
> except...
>
> 1. the patching process does not finish, because many tasks sleep in
> schedule. STOP/CONT signal does not help. I'll investigate.
Are these userspace processes or kthreads? Kthreads would cause
problems because they do not handle signals.
> 2. reversion of the process does not work as expected. The kernel
> crashes after the removal of the module. A task very likely slept in
> schedule and was not migrated properly. It might be because of the races
> in klp_reverse_transition() described by Petr, or might be somewhere
> else. I'll look into it.
I hope that I will be able to do another dive into the consistency
model patchset the following week.
Best Regards,
Petr
next prev parent reply other threads:[~2017-01-06 15:02 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-01-06 14:00 [PATCH] Documentation/livepatch: remove the limitation for schedule() patching Miroslav Benes
2017-01-06 15:01 ` Petr Mladek [this message]
2017-01-06 15:10 ` Miroslav Benes
2017-01-06 19:13 ` Josh Poimboeuf
2017-01-09 12:50 ` Miroslav Benes
2017-01-09 14:54 ` Josh Poimboeuf
2017-01-10 10:32 ` Miroslav Benes
2017-01-11 1:33 ` Jiri Kosina
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