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Date:   Tue, 17 May 2022 18:11:01 -0700
From:   "Paul E. McKenney" <paulmck@kernel.org>
To:     Chen Zhongjin <chenzhongjin@huawei.com>
Cc:     linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org,
        linux-arch@vger.kernel.org, linuxppc-dev@lists.ozlabs.org,
        stable@vger.kernel.org, peterz@infradead.org, tglx@linutronix.de,
        namit@vmware.com, gor@linux.ibm.com, rdunlap@infradead.org,
        mingo@kernel.org, jgross@suse.com, gregkh@linuxfoundation.org,
        mpe@ellerman.id.au
Subject: Re: [PATCH v4] locking/csd_lock: change csdlock_debug from
 early_param to __setup
Message-ID: <20220518011101.GK1790663@paulmck-ThinkPad-P17-Gen-1>
Reply-To: paulmck@kernel.org
References: <20220510094639.106661-1-chenzhongjin@huawei.com>
 <9b3e61b8-ecab-08ff-a3b6-83d6862ead77@huawei.com>
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On Tue, May 17, 2022 at 11:22:04AM +0800, Chen Zhongjin wrote:
> On 2022/5/10 17:46, Chen Zhongjin wrote:
> > csdlock_debug uses early_param and static_branch_enable() to enable
> > csd_lock_wait feature, which triggers a panic on arm64 with config:
> > CONFIG_SPARSEMEM=y
> > CONFIG_SPARSEMEM_VMEMMAP=n
> > 
> > With CONFIG_SPARSEMEM_VMEMMAP=n, __nr_to_section is called in
> > static_key_enable() and returns NULL which makes NULL dereference
> > because mem_section is initialized in sparse_init() which is later
> > than parse_early_param() stage.
> > 
> > For powerpc this is also broken, because early_param stage is
> > earlier than jump_label_init() so static_key_enable won't work.
> > powerpc throws an warning: "static key 'xxx' used before call
> > to jump_label_init()".
> > 
> > Thus, early_param is too early for csd_lock_wait to run
> > static_branch_enable(), so changes it to __setup to fix these.
> > 
> > Fixes: 8d0968cc6b8f ("locking/csd_lock: Add boot parameter for controlling CSD lock debugging")
> > Cc: stable@vger.kernel.org
> > Reported-by: Chen jingwen <chenjingwen6@huawei.com>
> > Signed-off-by: Chen Zhongjin <chenzhongjin@huawei.com>
> > ---
> > Change v3 -> v4:
> > Fix title and description because this fix is also applied
> > to powerpc.
> > For more detailed arm64 bug report see:
> > https://lore.kernel.org/linux-arm-kernel/e8715911-f835-059d-27f8-cc5f5ad30a07@huawei.com/t/
> > 
> > Change v2 -> v3:
> > Add module name in title
> > 
> > Change v1 -> v2:
> > Fix return 1 for __setup
> > ---
> >  kernel/smp.c | 4 ++--
> >  1 file changed, 2 insertions(+), 2 deletions(-)
> > 
> > diff --git a/kernel/smp.c b/kernel/smp.c
> > index 65a630f62363..381eb15cd28f 100644
> > --- a/kernel/smp.c
> > +++ b/kernel/smp.c
> > @@ -174,9 +174,9 @@ static int __init csdlock_debug(char *str)
> >  	if (val)
> >  		static_branch_enable(&csdlock_debug_enabled);
> >  
> > -	return 0;
> > +	return 1;
> >  }
> > -early_param("csdlock_debug", csdlock_debug);
> > +__setup("csdlock_debug=", csdlock_debug);
> >  
> >  static DEFINE_PER_CPU(call_single_data_t *, cur_csd);
> >  static DEFINE_PER_CPU(smp_call_func_t, cur_csd_func);
> 
> Ping for review. Thanks！

I have pulled it into -rcu for testing and further review.  It might
well need to go through some other path, though.

								Thanx, Paul