linux-kernel - Re: [PATCH] clk: Fix children not voting entire parent chain during init

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Date:   Mon, 29 Nov 2021 10:14:28 -0800
From:   Mike Tipton <quic_mdtipton@...cinc.com>
To:     <sboyd@...nel.org>, <mturquette@...libre.com>
CC:     <linux-clk@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] clk: Fix children not voting entire parent chain during
 init

On 11/8/2021 8:34 PM, Mike Tipton wrote:
> If a child's parent is set by calling __clk_init_parent() while the
> parent is still being registered in __clk_register(), then it can result
> in the child voting its direct parent without those votes propagating up
> the entire parent chain.
> 
> __clk_register() sets hw->core before grabbing the prepare_lock and
> before initializing hw->core->parent. Since hw->core is used indirectly
> by __clk_init_parent(), then children can find their parents before
> they're fully initialized. If children vote for their parents during
> this window, then those votes won't propagate past the direct parent.
> 
> This can happen when:
>      1. CRITICAL clocks are enabled in __clk_core_init().
>      2. Reparenting enabled orphans in clk_core_reparent_orphans_nolock().
> 
> Fix this by not setting hw->core until we've already grabbed the
> prepare_lock in __clk_core_init(). This prevents orphaned children from
> finding and voting their parents before the parents are fully
> initialized.
> 
> Fixes: fc0c209c147f ("clk: Allow parents to be specified without string names")
> Signed-off-by: Mike Tipton <quic_mdtipton@...cinc.com>
> ---
> 
> This is very difficult to reproduce. We can't reproduce it at all
> internally, in fact. But some customers are able to reproduce it fairly
> easily and this patch fixes it for them.
> 
>   drivers/clk/clk.c | 14 +++++++++++---
>   1 file changed, 11 insertions(+), 3 deletions(-)
> 

Reminder. We've had more reports of this and in each case this patch 
fixes the problem.