linux-kernel - [PATCH 4.9 168/175] soc: qcom: smp2p: Safely acquire spinlock without IRQs

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Date:   Mon, 28 Dec 2020 13:50:21 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org,
        Bjorn Andersson <bjorn.andersson@...aro.org>,
        Stephen Boyd <swboyd@...omium.org>,
        Evan Green <evgreen@...omium.org>
Subject: [PATCH 4.9 168/175] soc: qcom: smp2p: Safely acquire spinlock without IRQs

From: Evan Green <evgreen@...omium.org>

commit fc3e62e25c3896855b7c3d72df19ca6be3459c9f upstream.

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.

Cc: stable@...r.kernel.org
Fixes: 50e99641413e7 ("soc: qcom: smp2p: Qualcomm Shared Memory Point to Point")
Reviewed-by: Bjorn Andersson <bjorn.andersson@...aro.org>
Reviewed-by: Stephen Boyd <swboyd@...omium.org>
Signed-off-by: Evan Green <evgreen@...omium.org>
Link: https://lore.kernel.org/r/20200929133040.RESEND.1.Ideabf6dcdfc577cf39ce3d95b0e4aa1ac8b38f0c@changeid
Signed-off-by: Bjorn Andersson <bjorn.andersson@...aro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 drivers/soc/qcom/smp2p.c |    5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

--- a/drivers/soc/qcom/smp2p.c
+++ b/drivers/soc/qcom/smp2p.c
@@ -314,15 +314,16 @@ static int qcom_smp2p_inbound_entry(stru
 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);