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

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Message-ID: <160286690900.884498.13659438662199129460@swboyd.mtv.corp.google.com>
Date:   Fri, 16 Oct 2020 09:48:29 -0700
From:   Stephen Boyd <swboyd@...omium.org>
To:     Bjorn Andersson <bjorn.andersson@...aro.org>,
        Evan Green <evgreen@...omium.org>
Cc:     Markus Elfring <elfring@...rs.sourceforge.net>,
        Evan Green <evgreen@...omium.org>,
        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

Quoting Evan Green (2020-09-29 13:30:57)
> 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: Stephen Boyd <swboyd@...omium.org>