linux-kernel - Re: [PATCH] paravirt/locks: avoid modifying static key before jump_label

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Message-ID: <187967ca-a700-b770-90fe-ae8cd294b0d1@suse.com>
Date:   Fri, 27 Oct 2017 11:21:31 +0200
From:   Juergen Gross <jgross@...e.com>
To:     Ingo Molnar <mingo@...nel.org>
Cc:     linux-kernel@...r.kernel.org, x86@...nel.org, hpa@...or.com,
        tglx@...utronix.de, mingo@...hat.com, arnd@...db.de,
        peterz@...radead.org, Dou Liyang <douly.fnst@...fujitsu.com>
Subject: Re: [PATCH] paravirt/locks: avoid modifying static key before
 jump_label_init()

On 27/10/17 10:43, Ingo Molnar wrote:
> 
> * Juergen Gross <jgross@...e.com> wrote:
> 
>> Don't try to set the static virt_spin_lock_key to a value before
>> jump_label_init() has been called, as this will result in a WARN().
>>
>> Solve the problem by introducing a new lock_init() hook called after
>> jump_label_init() instead of doing the call inside of
>> smp_prepare_boot_cpu().
>>
>> Signed-off-by: Juergen Gross <jgross@...e.com>
>> ---
>> Based on kernel/git/tip/tip.git locking/core
> 
> Just a quick ping: what's the conclusion of the discussion, do we want this patch 
> as-is?

Dou Liyang (CC-ed) suggested another alternative he wanted to test. This
would be much less intrusive. I can send a patch based on his idea in
case he doesn't react in time: he basically suggested moving the call of
native_pv_lock_init() to native_smp_prepare_cpus() - this will need
another small adaption in Xen, but this is really simple.

> Also, it's unclear from the changelog under what circumstances this bug was 
> observed and what symptoms there are and how severe the bug - can the warning 
> trigger on vanilla v4.14?

No, the patch introducing the bug is in the tip tree only.


Juergen