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Subject: Re: [PATCH AUTOSEL for 4.15 104/124] clk: fix reentrancy of
 clk_enable() on UP systems
To:     Sasha Levin <Alexander.Levin@microsoft.com>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "stable@vger.kernel.org" <stable@vger.kernel.org>
Cc:     Stephen Boyd <sboyd@codeaurora.org>
References: <20180319154645.11350-1-alexander.levin@microsoft.com>
 <20180319154645.11350-104-alexander.levin@microsoft.com>
From:   David Lechner <david@lechnology.com>
Message-ID: <6a944b80-c86c-ca23-5ada-f088d84c9a80@lechnology.com>
Date:   Mon, 19 Mar 2018 10:55:16 -0500
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On 03/19/2018 10:48 AM, Sasha Levin wrote:
> From: David Lechner <david@lechnology.com>
> 
> [ Upstream commit a12aa8a68dfef5de181f2e555aa950a0ab05411f ]
> 
> Reentrant calls to clk_enable() are not working on UP systems. This is
> caused by the fact spin_trylock_irqsave() always returns true when
> CONFIG_SMP=n (and CONFIG_DEBUG_SPINLOCK=n) which causes the reference
> counting to not work correctly when clk_enable_lock() is called twice
> before clk_enable_unlock() is called (this happens when clk_enable()
> is called from within another clk_enable()).
> 
> This fixes the problem by skipping the call to spin_trylock_irqsave() on UP
> systems and relying solely on reference counting. We also make sure to set
> flags in this case so that we are not returning an uninitialized value.
> 
> Suggested-by: Stephen Boyd <sboyd@codeaurora.org>
> Signed-off-by: David Lechner <david@lechnology.com>
> Signed-off-by: Stephen Boyd <sboyd@codeaurora.org>
> Signed-off-by: Sasha Levin <alexander.levin@microsoft.com>
> ---

I don't know of any existing bugs in v4.15 that this fixes, so I don't
think this really fits the criteria for stable.