linux-kernel - Re: [RESEND PATCH] soc: qcom: smp2p: Safely acquire spinlock without IRQs

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Message-ID: <20201016171337.GA241575@builder.lan>
Date:   Fri, 16 Oct 2020 12:13:37 -0500
From:   Bjorn Andersson <bjorn.andersson@...aro.org>
To:     Evan Green <evgreen@...omium.org>
Cc:     Markus Elfring <elfring@...rs.sourceforge.net>,
        Andy Gross <agross@...nel.org>, linux-arm-msm@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [RESEND PATCH] soc: qcom: smp2p: Safely acquire spinlock without
 IRQs

On Tue 29 Sep 15:30 CDT 2020, Evan Green wrote:

> smp2p_update_bits() should disable interrupts when it acquires its
> spinlock. This is important because without the _irqsave, a priority
> inversion can occur.
> 
> This function is called both with interrupts enabled in
> qcom_q6v5_request_stop(), and with interrupts disabled in
> ipa_smp2p_panic_notifier(). IRQ handling of spinlocks should be
> consistent to avoid the panic notifier deadlocking because it's
> sitting on the thread that's already got the lock via _request_stop().
> 
> Found via lockdep.
> 
> Fixes: 50e99641413e7 ("soc: qcom: smp2p: Qualcomm Shared Memory Point to Point")
> Signed-off-by: Evan Green <evgreen@...omium.org>

Reviewed-by: Bjorn Andersson <bjorn.andersson@...aro.org>

Regards,
Bjorn

> ---
> 
>  drivers/soc/qcom/smp2p.c | 5 +++--
>  1 file changed, 3 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/soc/qcom/smp2p.c b/drivers/soc/qcom/smp2p.c
> index 07183d731d747..a9709aae54abb 100644
> --- a/drivers/soc/qcom/smp2p.c
> +++ b/drivers/soc/qcom/smp2p.c
> @@ -318,15 +318,16 @@ static int qcom_smp2p_inbound_entry(struct qcom_smp2p *smp2p,
>  static int smp2p_update_bits(void *data, u32 mask, u32 value)
>  {
>  	struct smp2p_entry *entry = data;
> +	unsigned long flags;
>  	u32 orig;
>  	u32 val;
>  
> -	spin_lock(&entry->lock);
> +	spin_lock_irqsave(&entry->lock, flags);
>  	val = orig = readl(entry->value);
>  	val &= ~mask;
>  	val |= value;
>  	writel(val, entry->value);
> -	spin_unlock(&entry->lock);
> +	spin_unlock_irqrestore(&entry->lock, flags);
>  
>  	if (val != orig)
>  		qcom_smp2p_kick(entry->smp2p);
> -- 
> 2.26.2
>