lkml.org 
[lkml]   [2017]   [Jan]   [10]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [PATCH] Documentation/livepatch: remove the limitation for schedule() patching
On Fri, 6 Jan 2017, 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>
> ---
> 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.
>
> 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.

Applied, thanks.

--
Jiri Kosina
SUSE Labs

\
 
 \ /
  Last update: 2017-01-11 02:34    [W:0.264 / U:0.108 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site